Quick digiKam Tip: Back up digikamrc file

digiKam stores the current state of the application in the ~/.config/digikamrc file. This file keeps track of pretty much everything: from the database connection profile and custom toolbar settings, to the last-used curve and sharpening parameters. So next time you install or reinstall digiKam, don’t forget to back up the digikamrc file. This way, you don’t have to configure a fresh digiKam installation from scratch. Simply copy the file to a safe location or external storage device, and drop the file into the ~/.config folder before you run digiKam.

Location Tracking for Photographers with GPS Logger and Trekarta

When it comes to Android apps for photographers, we are spoiled for choice. From depth-of-field and golden hour calculators to sun position and remote control apps – there are plenty of clever tools to choose from. But there is one particular app combination that can prove to be indispensable for any photographer on the move: a GPS logger and a GPX viewer. There are two main reasons for that.

1. Tracking your movements and saving them in the GPX format can come in handy for geotagging photos.

2. The ability to attach comments to the current location allows you to use the GPS logging app to note places you either photographed or you plan to photograph later. You can then use a GPX viewer app to see and manage bookmarked locations.

There are several apps that offer GPS logging and viewing, but you can’t go wrong with GPS Logger for Android and Trekarta. Both apps are released under an open source license, and they are available free of charge on Google Play and F-Droid.

How you set up GPS Logger for Android is a matter of personal preference. One way to go is to configure the app to automatically start tracking on boot and upload tracks to the desired destination (e.g., a NAS or a file sharing service).

Once GPS Logger for Android is running, adding a comment to the current location is as easy as pulling down the notification drawer and tapping Comment. The app saves the tracks as GPX files in the Android/data/com.mendhak.gpslogger/files directory on your Android device. To view a GPX file in Trekarta, use a file manager to navigate to the directory, and use Android’s sharing functionality to send the desired GPX file to Trekarta.

Processing a nightscape in Siril

A basic tutorial

Siril is a program for processing astronomical photographs.

In this tutorial, I’ll show you how to process a nightscape in Siril 0.9.10.

It doesn’t intend to be comprehensive tutorial but rather to present a basic general workflow that is a good starting point for those who want to learn Siril.

For this purpose, I’m sharing the raw files I used for the image I presented here, except that for this tutorial I limited the number of frames for the sake of bandwidth and processing speed.

You can find and download the raw files here (~1GB).

Setup

The raw files are placed in specific sub-folders according to their use:

• bias/offset frames → ./Bias (20 files)
• dark frames → ./Darks (15 files)
• flats field frames → ./Flats (15 files)
• main subject/light frames → ./Lights (10 files)

Bias, dark, and flat field frames are also called “calibration” frames, their purpose being to improve the quality of the image by correcting the signal-to-noise ratio (in the case of bias and dark frames) and vignetting (with the flat frames). There are several places where you can learn more about the different types of frames for astrophotography.

At the root of the folder, I placed two text files with the .ssf extension, these are scripts used by Siril for batch processing the files. Quite useful. If you want to run a script from Siril, place the .ssf files in ~/.siril/scripts. Upon restarting Siril, a new Scripts menu appears in the top menu bar, allowing you to launch the installed scripts.

I suggest you download the whole folder (~1GB), and move the scripts as indicated above. This way, if you set the working directory in Siril to the root of the folder, launching the script named processing_from_raw.ssf will automagically process the raws and create the output image in both .fit and .tif (16-bit) formats. Please note that in order to successfuly run the scripts, there must be a folder structure like the one used in this tutorial.

Step-by-step processing

I will present the steps I used to process an image of the Milky Way. I don’t know if it’s the best way, but it’s probably close to what the developers of Siril advise to do for the general case of starting from raw files (actually, I started from one of their scripts and just slightly adapted it).

We will start with processing the calibration files, and then processing the lights.

Preparing the bias frames

1. Set the working directory to the Bias sub-folder by clicking on Change dir….

2. We will use the 20 bias frames to generate a master-bias frame. To load the bias frames, click on the + button as shown (make sure that you select RAW DSLR Camera Files in the combo box) and select the bias frames located in the Bias subfolder.

3. In the “Sequence name” field, enter bias (or whatever you see fit) to set the prefix of the sequence and subsequent files, and click Convert to convert the files to the FITS format, which is the main format used by Siril. Note that you don’t need to demosaic the files yet, make sure the Debayer box is unchecked.

When done converting the bias frames, a window will pop up showing a preview of one of the bias frames. Note that since it’s not demosaiced, it will only show as a B&W channel image.

At this point, the bias frames are loaded and ready to be processed to make a master-bias frame.

4. In the Stacking tab, choose Average stacking with rejection as stacking method, and No normalisation under the normalisation combo box. You can leave the Sigma parameters at their default (unless you know or want to experiment for better values).

It should look like this:

5. Click on the Start stacking button. The resulting master-bias frame will be saved as bias_stacked.fit in the Bias subfolder.

Preparing the flat field frames

Since the flats also contain the sensor readout noise (contained in the bias frames), we should remove it by subtracting the master-bias.

1. In the File conversion tab, remove the files already loaded by clicking on the button located just below the - (minus) button, and by clicking on the + (plus) button select and load the flat frames located in the Flats subfolder.

2. Set the working directory to the Flats sub-folder by clicking on “Change dir…” and set the Sequence name as “flats”.

3. Like for the bias frames, ensure Debayer is unchecked, then click on Convert.

4. In the Pre-processing tab, check only the Use offset box, click on Browse to select the Bias/bias_stacked.fit file, and click on Start pre-processing.

5. To generate the master-flat, go to the Stacking tab, and this time set Normalisation to Multiplicative and the Stacking Method as Average with rejection.

6. Click on Start stacking to produce the pp_flat_stacked.fit master-flat frame in the Flats subfolder.

Preparing the dark frames

As with the bias and flats, you need to load the dark frames.

1. In the File conversion tab, remove the files already loaded, select and load the dark frames located in the Darks subfolder.

2. Set the working directory to the Darks sub-folder by clicking on Change dir…, and set Sequence name as darks.

3. Debayer should be unchecked.

4. Click on Convert.

5. The darks need to be stacked the same way as the bias frames. In the Stacking tab, choose Average with rejection and No normalisation.

6. Click Start Stacking.

The master-dark frame is saved as Darks/dark_stacked.fit.

Note: if you take images often in the same conditions (same air temperature, same exposure settings), you can save the dark_stacked and pp_flat_stacked files, and re-use them to process future light frames faster. I read on some forums that some astrophotographers keep their calibration files and use those for around 1 year, before taking new calibration frames.

Preparing the light frames

Now it’s time to start processing the light frames, by first subtracting the darks (which also contain the bias signal) and the flats (from which bias has already been subtracted).

1. Select the light frames in the File conversion tab.

2. Set the Sequence name to lights, and point the working directory to the Lights (Change dir...).

3. Convert the files, still without debayering.

4. Then go to the Pre-Processing tab, check Use dark, select the Darks/dark_stacked.fit file, check Use flat, and select the Flats/pp_flat_stacked.fit file.

5. Make sure that the other boxes are checked as in the following screenshot.

Note that “Cosmetic Correction” can also be done from the “Image Processing” tab.

6. Click Start pre-processing.

This will produce new FITS files with the prefix pp_light_ and the corresponding .seq file. These files are loaded.

Demosaicing the files

It’s time to demosaic our processed files. There’s something strange in the GUI, in that after pre-processing, when you uncheck “Use dark” and “Use flat” boxes, the “Debayer FITS images before saving” and the “Start pre-processing” button become grayed out.

1. In the File conversion tab, remove the selected files and load the 10 pp_light_000xx.fit files.
2. Check the Debayer box and write db_pp_light as the sequence name.
3. Click Convert.

The pre-processed lights will be saved as FITS files, and the corresponding db_pp_light.seq file loaded. Two preview windows will open this time, one with the 3 RGB channels separated, and one with the RGB composite image.

4. In the Register tab, select Global Star Alignment (deep-sky) from the registratrion method drop-down list and click Go register.

If you have more 8GB of RAM, you can try checking the Simplified Drizzle x2 box (it will up-sample the images by a factor 2, increasing the RAM usage by a factor 4). Siril will detect the stars and register each of the 10 images. The preview windows will be updated. By the way, you can play with the zoom and select AutoStretch to get a better preview of the selected image.

5. In the Stacking tab, make sure that Average with rejection is selected as the stacking method, and that Additive with scaling is set for Normalisation.

6. Click on Start stacking.

The resulting aligned and stacked image will be saved as Lights\r_db_pp_light_stacked.fit.

7. At this step, you can also save the resulting image as JPEG, TIFF, PNG, etc. for further processing in your favorite image editor. On the menu, just click on File > Save As, and pick the image format you wish (or right-click on the RGB windows and pick the format that best suits you).

Post-processing the image

Siril can do some more or less specialized post-processing to your image. I found it interesting to use.

• While the stacked image is still loaded in Siril, you can apply a log transform (it is in linear mode in Siril). I haven’t found how to do it in the GUI, but you can simply type “log” in the “Console” field at the bottom of the Output logs tab, in the main window.
• Still in the console field, you can use the command “crop” followed by the coordinates of the bounding box in pixels, to crop the image (some auto-detection tools in Siril require the image to be cropped to remove the borders introduced by aligning the images, in order to work properly). For example, my image can be cropped by typing crop 30 30 5950 3970.
• You can apply green noise removal in the “Image Processing” tab > “Remove Green Noise…”.
• Lucy-Richardson deconvolution can be applied in “Image Processing” menu option > “Deconvolution…”. 10 iterations and a Sigma value of 0.6 are a good starting point.

The resulting image can be saved as JPEG, TIFF, PNG, etc. for further processing in your favorite image editor or as a finished image if you’re satisfied.

Processing for the foreground

The problem with this whole process, is that because the images have been aligned with the stars as reference, the foreground will be blurred because earth moved between successive frames. What I do is to reprocess the light frames from just after the calibration step (i.e. after the dark and flat frames subtraction) but only skipping the stars registration step. By doing so, the foreground will undergo the same pre- and post-processing, and the resulting image will have a sharp foreground and trailing sky.

I provided a script (processing_from_raw_foreground.ssf) which will do that for you, if you already used the first script or if you use the same file naming convention as in the script.

Finally, in your favorite image editor, you can combine the “sky” and “foreground” images using a mask, to get both the sky and the foreground sharp.

Here’s what I obtained following these steps (but using the scripts), after just combining the 2 images in Gimp:

And after quick curve and saturation tweaking in Gimp:

New Topic Previews

Image previews now available for some categories

I’ve been a member of the community over at blenderartists.org (previously elysiun) for a long time (it’ll be 15 years this October according to my profile there). So it was nice to see when they finally transitioned to using Discourse a little while back.

What I really liked, though, was the work that Bart did to specific pages and tag lists to display them. Here’s what their current homepage looks like:

They use a different default main page style, “Categories” view, than we do (“Latest”). This just shows the site categories as a column on the left, then the latest posts in a column on the right.

The row of featured images along the top is actually part of a plugin that I’ll get to in a moment.

If you want to change your own default main page view of the forums, you can modify it at your account Preferences → Interface (and change it to Categories):

Fancy Category Views

The default landing page is neat, but what they did with their forum gallery page is much neater:

They set up the Topic List Previews plugin so the entire category is actually viewed as a tile of images. I think we can all agree that this is generally a much nicer way to view categories that are heavily image-based. Of course, I thought this was a natural fit for us as well!

So through the magic of having an invaluable resource like a darix, he was able to make it a reality for us!

We’ve got it implemented now on the Play Raw category (now its own sub-category under the Processing category), the Critique, and the Showcase category. If you haven’t had a chance to check it out yet, please do. (darix announced it in the thread Play raw posts and you so feel free to give us any further feedback in that topic.)

Keep in mind that for those categories, the preview image will correspond to the first image in the first post. Try to remember to make the first image in those category topics the one you’ll want in the preview.

We haven’t enabled the featured row of images after some initial feedback. We may revisit it again at some point, but hopefully the Play Raw and Showcase categories will look a little better now. It certainly makes the categories a little easier and faster to navigate now that you can see the previews directly on the page.

G'MIC Finally Accepts Donations

Help support an awesome team!

For years the incredible team over at G’MIC (GREYC’s Magic for Image Computing) have been producing an incredible image processing system and many awesome filters to go along with it. They’ve got an very active and awesome community right here on their forums and they’ve been producing all manner of neat processing filters for photographers, digital artists, and scientists.

Due to the project being under the auspices of a French Research Lab, the GREYC laboratory in Caen, France, they were limited in being able to accept any donations.

Until now!

To avoid burying the lede, go and make a donation to the fabulous folks of the G’MIC project: https://libreart.info/en/projects/gmic.

I first heard about GREYCstoration (proto-G’MIC) a long time ago (over 10 years) as the only really viable Free Software image denoising option for photographers. It allowed me to de-noise images on par (or better in many cases) with the then popular Noise Ninja. It’s been an essential part of my toolkit ever since!

Back then David Tschumperlé was really only looking for postcards from users as a “thank you” and maybe some occasional donations to pay for hot chocolates during the day. I finally got to buy him a milkshake while at the Libre Graphics Meeting 2014 in Leipzig, Germany and for the value he has provided me with his software I owe him many, many more!

Value is exactly what I want to bring up in this post. I’m sure many here have had an opportunity to use G’MIC in some form and any attempt at listing the wide range of filters and capabilities it provides would not do it justice. If you’ve realized some value from the project, now is the time to show some love.

I’ve been lucky to call David a friend for a long time now and I can personally attest to his kindness and sincerity. With that in mind I implore you: if you have a few spare dollars, euros, yen, pesos, or gold bullion please consider donating to the project and make sure the milkshakes (or hot chocolates) never stop flowing. David (and Sébastien Fourey!) are a sound investment in providing high value to Free Software artists and photographers!

Donate to the G’MIC project!

(David is too modest to really come out and ask for support but “modest” isn’t really in my vocabulary - so go donate!)

LILA

For a long time David was unable to accept donations from community members. There were some concerns from the research institution his lab is a part of in France. Just recently, though, they managed to reach an agreement where the funds flow through a French non-profit called Libre Comme L’Art, LILA, that includes the fabulous Jehan Pagès of the GIMP team as a member and where the ZeMarmot animated film is being produced.

A big “Thank You!” to Jehan and LILA for making this possible!

A Q&A with the CHDK Developers

Adding Features to a Camera: Hacker Meets Photographer

Introduction

CHDK is a free, open source software add-on that runs on Canon PowerShot cameras and expands their functionality. Some of its features are:

• Professional control: RAW files, bracketing, manual control over exposure, zebra mode, live histogram, grids, etc.
• Motion detection: Trigger exposure in response to motion, fast enough to catch lightning.
• USB remote: Simple DIY remote allows you to control your camera remotely.
• Scripting: Control CHDK and camera features using uBASIC and Lua scripts. Enables time lapse, motion detection, advanced bracketing, and more.
• PTP: Shooting control, live view, and file transfer from Linux and Windows.

I talked with the core team of developers to learn more about CHDK.

How did CHDK start? Who were the first developers? What was their role in those first steps? Do you have any information on who those people are, where they come from, or their professional background?

reyalp: That was before my time. The very first developer was VitalyB, and I don’t know much about his background.

In truth, CHDK is very loosely organized and informal, so I don’t know much about current contributors backgrounds either.

waterwingz: Before my time too. The original hack seems to have taken off in 2006/2007 when it got mention on the dpreview.com site. Many people shared random bits and pieces based on what they were personally interested in working on. There was no project organization and people did their own builds.

At some point, I believe someone with the nick GrAnd, got things organized around a wikia site and created a standardized set of build tools. Eventually an online discussion forum and autobuild server were added - not sure who gets credit for those.

But over the last 10 years, more or less, reyalp has coordinated the ongoing volunteer development efforts. There is still no real plan or schedule but there seems to be community consensus of how things get done and what gets added to the package.

Some people say that CHDK was first developed by Andrei Gratchev (here and here). I believe he is GrAnd, right? Do you know something about it? Is it possible that Andrei Gratchev is VitalyB?

reyalp: GrAnd (Andrei Gratchev) and VitalyB are definitely not the same person. They have separate accounts on assembla.com. VitalyB did the very first work on what eventually became CHDK, while GrAnd was an early developer who played a major role in organizing the project. It’s possible that GrAnd originated the name CHDK. I don’t know that history directly, but it could explain confusion over whether he was the founder.

Canon cameras run on DIGIC boards. As far as I’m aware of, at the time VitalyB did the first hack, people had already hacked DIGIC-I compact Canon cameras and could execute custom programs. What was the big leap (in terms of development or finding hooks in the DIGIC-II firmware) that VitalyB made?

reyalp: The original Digic-I cameras were actually ROM DOS running on a 16 bit x86 clone (except for S1 IS, which is VxWorks on ARM and has a partial CHDK port developed by srsa_4c).

A hack for the DOS based cameras was developed by a Czech developer.

I don’t know if VitalyB was aware of this work, but the platforms were so different there wouldn’t likely have been much overlap.

waterwingz: As far as I know, the big leap in hooking the DIGIC-II firmware was figuring out how to hack Canon’s firmware update process.

It’s stated that he hacked the firmware update process and executed his own program instead of the firmware update itself. That first program aimed to make a copy of Canon firmware. How exactly could he get a copy of the Canon firmware by blinking a LED? Why did he need a copy of Canon firmware?

waterwingz: From what I understand, he assembled a little piece of code that loaded and ran in the place of the expected firmware update code.

Once he could do that, by trial & error he learned what memory address needed to be poked to turn one of the camera’s LEDs on & off. And once he could do that, he recoded so as to dump the camera’s memory contents serially via that LED to a phototransistor interfaced to an external computer.

After that it was a matter of reverse assembly of the raw code to learn how the rest of the boot process and camera firmware worked.

reyalp: I don’t know the specifics of exactly what VitalyB did for the very first camera, but generally to make a hack work with the existing firmware, you need a copy of the firmware code to disassemble and analyze.

The advantage of using LED blinking is that the code is really simple: you just need to know how to control an LED (done writing to specific address on these cameras) and a loop.

In contrast, writing a file to the SD card requires a whole stack with an SD driver, a filesystem driver and so on.

Without having already analyzed the firmware, you don’t know how to interface with those things, and on PowerShot cameras, they aren’t really available after a firmware update file is loaded.

Blinking was used frequently in the early days of CHDK, but around 2010 Alfredo Ortega and Oren Isacson of Core Labs worked out how to run scripts in Canon’s native scripting language (which we call Canon Basic). I wrote a script to dump the original firmware from Canon Basic, and we’ve used that as the primary way of dumping firmware ever since.

Canon DSLR’s also allow this same kind of hack. Why did VitalyB start with point-and-shoot cameras?

waterwingz: I’m guessing, but probably he started there because he happened to own a PowerShot and not a DSLR. Or maybe it was just the first device that he was able to find a backdoor into.

reyalp: While Canon DSLRs and P&S use the same basic CPU and operating systems, the rest of the code is very different.

Running custom code on Canon DSLRs uses different mechanisms which weren’t figured out until much later.

My impression is VitalyB started on the camera he had (PowerShot A610?).

The lower cost of P&S also makes them more attractive to experiment with, and before the rise of smartphones, P&S were much more common than DSLRs so there was a better chance of interested developers having them.

Are there any ties between CHDK and Magic Lantern (a CHDK equivalent for Canon DSLRs)?

waterwingz: There are several people who participate in both projects and some discoveries are occasionally useful to both. But there is no coordination beyond that.

reyalp: We do share information and occasionally code, but as mentioned above, the Canon firmware up to now has been quite different. Some of the initial DSLR research took place on the CHDK forum.

CHDK was born as HDK, or Hack Development Kit, and only later the “C” was added. Regarding the idea behind the name, what exactly does it mean to say that CHDK is not a simple firmware add-on, but a development kit? Does it have to do with the capability of loading and executing custom user scripts?

waterwingz: Way before my time again - I’d only be speculating on the name’s origin. I guess the kit designation means you get the source code to do development with. I don’t think it has anything to do with user scripting capabilities.

Is this kind of hack only possible on Canon cameras? Why?

waterwingz: The exact details and mechanism will only work on Canon PowerShot cameras. They all build on how Canon supports firmware upgrades (even though CHDK does not actually modify any of the camera’s firmware).

To do something similar on a different brand of camera, you’d need to find a way to exploit any firmware update method they might provide. If there is no such mechanism, you’d need to get lucky and find some other vector.

reyalp: As waterwingz says, the specifics only apply to these cameras, but in general, most embedded devices are hackable with enough effort.

Manufacturers put varying levels of effort into preventing it, but the success of CHDK (and later Magic Lantern) involves a lot of stuff that just lined up by chance.

Another important factor in these projects is that reverse engineering is additive: the more you build and understand, the easier it is to keep up with upstream changes in new models. It’s also easier for people to add useful features, which gets more people involved and keeps the whole thing going.

Getting to that critical point on an entirely new system requires a lot of effort and/or luck.

Some of the lucky things that lined up to make CHDK take off were:

• The cameras ran VxWorks on ARM 946E-S, both of which had significant public documentation. Canon later switched to their proprietary DryOS operating system, but by that point CHDK had enough built up knowledge to carry on.
• Canon left a lot of diagnostic stuff in the code and didn’t put a lot of effort into stopping unauthorized code from running.
• There were a lot of PowerShots in circulation and they were affordable, which provided more chances of a developer with the reverse engineering skills having one.
• Canon didn’t make any effort to stop it.

Can authorized warranty repair shops refuse to service cameras because of CHDK? Does CHDK use leave any traces?

waterwingz: So far it has not been a problem as CHDK runs in RAM - it makes no permanent changes to the camera. When you turn the camera off, it disappears and you have to reload it the next time you use it.

And while Canon has made no official statements about CHDK one way or the other, there is an email somewhere from someone in Canon tech service stating that as long as CHDK did not modify the camera in any way, there was no warranty issue.

If you remove the SD card containing CHDK prior to sending your camera for service, there is really no way of anyone knowing you’ve used CHDK.

reyalp: CHDK doesn’t normally leave obvious traces, but if the camera crashes, traces of CHDK can appear in an internal crash log the Canon firmware stores in onboard flash memory.

It’s certainly possible that other traces could be present, the cameras have a lot of sub-components that could store their own diagnostic information.

I don’t recall any cases of anyone reporting having warranty service rejected for this, but that doesn’t mean it couldn’t happen.

Could you give a brief explanation of how CHDK is designed? Do you have any kind of diagram that could illustrate it?

waterwingz: CHDK is a volunteer effort and most volunteers would rather code than document in detail.

But you can learn a lot reading the For Developers section of the CHDK Wikia.

A short description is that CHDK loads by hijacking the camera’s firmware update process and then intercepts some of the camera’s RTOS tasks and replaces them with its own tasks. The CHDK tasks typically replicate the functionality of the original camera tasks but add features and functionality not included in the original Canon code.

In what language is CHDK built?

waterwingz: A combination of ARM assembler and C.

philmoz: I would add Lua to that - a lot of useful features are now in the scripts. waterwingz has built some impressive functionality with his scripts.

I suppose we should also include uBasic as we still include some testing scripts written in it. uBasic is very primitive compared to Lua, so Lua scripts are preferred.

Finally there is also the Canon Basic built into the firmware - we use this to do firmware dumping.

What were some of the difficult issues in making CHDK easier to port to new cameras?

waterwingz: Ummm… who said it was easy?

But seriously, most of CHDK is based on guesses about how the original Canon hardware and firmware works. So much of the coding was done on a “try it and see” basis.

What makes it more difficult is changes to the firmware as Canon changes RTOS’s or generations of DIGIC processors.

philmoz: The Canon firmware remained pretty stable for a while. It continued to evolve but there weren’t any real upheavals until Digic 6. This made it easier to improve the tools, and take some of the guesswork out of ports.

We have a “sig finder“ tool that analyses a firmware dump and tries to find the things needed for a port. When I first started this was pretty primitive and a lot of things had to be done manually. I spent some time improving this tool, and I think that made porting a bit quicker until Digic 6.

waterwingz also created a GUI tool for disassembling the firmware in a way that could be used in a port - I added a scripting language to this to automate the generation of some of the files needed for a port, which I think helped with new ports.

With Digic 6 the architecture changed a lot and things slowed down quite a bit. A lot of reverse engineering on the new cameras has been done by srsa_4c, reyalp, ant, and others so things are getting better again.

reyalp: One of the things that makes it difficult is how many there are. The official CHDK source supports over 150 distinct models (many with multiple firmware versions that each require distinct ports), spanning Canon releases from 2004 through 2015.

Essentially the same CHDK code runs on all of them, so if a new model does something different, you have to figure out how to accommodate it without breaking the existing cameras.

On top of that, the developers don’t own most of the cameras, so testing is difficult.

As Philmoz mentioned, with Digic 6, Canon moved to a ARMv7 architecture processor and a new display system with a TAKUMI GPU, which took a lot of work supporting. srsa_4c did much of the initial reverse engineering work, while I took the concepts from Philmoz‘s “sig finder“ and implemented them in a new tool based on the open source Capstone disassembly library.

nafraf: The scripting language developed by Philmoz helped a lot to port until Digic 5+ cameras. Using code_gen tool it was possible to port new models and improve the existing ports. On release 1.3, for example, code_gen was the key tool to add more than 60s exposure on all cameras.

In which OS do these tools run?

waterwingz: CHDK is built using the gcc compiler so I guess the tools run on anything that supports that compiler - Windows and Linux for sure.

I do all my work under Linux although I have a laptop somewhere that runs the Windows tools.

The autobuild server that rebuilds CHDK after each update and provides current downloads runs under Linux.

And there are quite a few other tools that people have created, some of which are Windows only (or using Wine under Linux) and some of which are Java based and will run on Windows, Linux, or MacOS.

philmoz: I use MacOS for CHDK development.

I also have a Linux VM I use for testing batch builds of the entire set of supported cameras, to make sure big changes don’t break the autobuild server.

reyalp: I use Windows on my primary development system, but all the core CHDK tools and build process have supported Linux for as long as I’ve been involved.

My normal CHDK development environment is MSYS shells and gvim.

I also use Linux in VMs and a Raspberry Pi for some things.

Is there any camera emulator that allows to test core code before loading it into the camera?

waterwingz: There are a couple of clever GUI emulators for testing CHDK uBASIC and Lua scripts.

But I don’t believe anyone has really succeeded in making a QEMU emulator for core code development.

All testing is done on actual cameras.

And to date, I don’t believe anyone in the dev community has bricked a camera which says something about the stability of the process!

philmoz: Magic Lantern uses QEMU to run their code in an emulator.

In theory CHDK could do this as well, but to date no-one has invested the time to create the hardware simulation bits needed.

Debugging CHDK is old school - blinking LED’s, printing messages (if you have the display working), writing log files, and lots of trial and error.

reyalp: Not emulation, but I use chdkptp a lot for interactive testing. Being able to dump bits of memory or call functions interactively from a PC console is very useful.

What’s the easiest way for someone to get involved with CHDK?

waterwingz: Download it and use it on a PowerShot.

Learn what it does and how to run scripts.

Then write some scripts on your own, or modify some existing ones.

Finally, do a port for an unsupported camera - pretty much every CHDK dev started off porting and then got hooked on doing more.

blackhole: The easiest way is to use CHDK for something creative. It’s nice to see when users show results that are the product of using CHDK. I think it’s the biggest reward for developers when they see that their work is well-used.

reyalp: The forum is the best place to get involved with the community.

To get involved with development, it really depends on your interests. If there’s something you want to add, either dive into the code or ask for suggestions on where to start.

Ports of additional cameras are always welcome too, and doing one provides a good overview of how CHDK works.

What are some tasks non-programmers can do to help the project?

waterwingz: There has been a lot of work on the CHDK wiki over the years, but there is still a ton to do.

For example, one CHDK user finds time each month to simply correct spelling and the worst of the grammar mistakes on the more popular pages and the CHDK User Manual.

reyalp: If you do something interesting with CHDK, share it in the forum. A lot of interesting projects start as riffs on something someone else explored years earlier.

Documentation always needs help, but for CHDK, a lot of it really requires careful experimentation or knowledge of the source to do well.

nafraf: If you are a CHDK user and find a bug, or a missing function on the port of your camera, please report the bug to the forum and help to test new versions.

Developers don’t have access to all models, then testing and receiving feedback from the users are necessary to help the project.

How healthy is the production of user scripts? Is it easy for a non-programmer to write a script? In what languages?

waterwingz: The huge improvements in mobile phone cameras have really impacted the market for all but the highest end or largest zoom P&S cameras.

Having said that, a core of serious photographers still work on what interests them and depend on CHDK to help capture their artistic vision.

As far as non programmers and script writing, uBASIC is about as simple as a computer language gets and there are lots of example scripts to study.

Lua provides a much richer programming environment, albeit with a bit of a learning curve.

reyalp: Easy… depends on the user.

Because CHDK is a reverse engineered hack on top of an undocumented system, many behaviors are not well specified or understood.

waterwingz improved things a lot by creating a comprehensive reference of CHDK script functions, but developing non-trivial scripts still requires significant effort and a willingness to experiment.

I’ve been using CHDK for 10+ years, and still find myself greping the CHDK source and making test cases to figure out what functions actually do.

All that said, I don’t think learning to write modest CHDK scripts is particularly harder than starting out with javascript or batch files or that sort of thing.

We should note CHDK uBASIC is based on Adam Dunkels code, not the UBASIC written by Yuji Kida for mathematical computing.

How many developers work on CHDK? How does it work?

waterwingz: There have been hundreds of contributors to CHDK over the years.

Currently there is an active core of two or three people doing original work with low level firmware stuff, a couple of people working more on the user experience, several people generating custom scripts for unique photographic opportunities, and a core of maybe ten CHDK experts not doing much coding these days but continuing to provide support to the community.

What uses are people making of CHDK? Is there any that should be highlighted?

waterwingz: There is a nice list on the main page of the CHDK Wiki - unique things like motion triggering, scripting, RAW/DNG, bracketing, and full manual exposure control.

Originally, there was a lot of interest in just getting RAW files from an inexpensive P&S camera.

More recently the focus has been on making good multi-camera rigs with full centralized control using CHDK’s PTP capability. Everything from book scanners, “bullet time” rigs, to full 3D capture for building small replicas of people. And of course the ongoing interest in time lapse videos and kite and drone photography work.

reyalp: I get a kick out of how many different things show up searching google scholar for “CHDK hack”

Currently, what is the main development effort underway? New functionality? Porting CHDK to new camera models?

waterwingz: A lot of the current development is focused on very detailed features that interest the core developers. Not really anything that will revolutionize the CHDK user experience right away unfortunately.

But there are also potentially some interesting new things in the wings if the devs working on them can ever get them finished.

reyalp: There aren’t really any major features undergoing significant development right now.

There are some ideas and experimental stuff being kicked around, like the GUI concept and some work on capturing raw outside the normal shooting process, but what eventually gets added depends on developers time and interest.

I’m trying to wrap up a few things to release CHDK 1.5 before we start major projects in the official development branch.

So there’s a new CHDK GUI underway, and it seems very interesting and more user oriented. Once finished, how will it be released to the many different camera models that already run CHDK?

waterwingz: Oh oh - you noticed that? Did you also see the comment about the dev working on it not being too good at it getting finished? ;)

For what it’s worth, there has been quite a bit of thought about keeping it generic enough so that will run on all CHDK capable cameras. That’s mostly about screen resolution issues but there will probably be other challenges. Touchscreen cameras like the PowerShot N come to mind.

What is the future of CHDK, considering the evolution of technology? How long do you think point-and-shoot cameras will stay on the market, given the rise of smartphones? Do you think the latter will replace the former?

waterwingz: As I mentioned earlier, smart phone cameras continue to improve and that has impacted the low end PowerShots that CHDK does so much for.

CHDK will continue as an interesting project as long as a people enjoy using it and creating new things with it.

blackhole: The P&S cameras with the large zoom will likely survive the competition of smartphones. Smartphones in this area will not be competitive with cameras for a long time. CHDK is likely to have a future in this area.

philmoz: I think there will also be demand for the higher end P&S cameras with larger sensors, although I don’t think the market will be huge.

The number of people with these cameras interested in CHDK is probably going to be pretty small.

Canon’s EOS-M mirrorless cameras can also run CHDK so there is some interest there.

reyalp: Low end, mass market P&S are clearly on the way out. I agree with blackhole and philmoz that higher end stuff will be around for a while to come, but the possibility of running CHDK on future cameras is always uncertain.

As I mentioned earlier, Canon DSLRs and P&S cameras have been based on different codebases, which are different enough that it doesn’t make sense to run the same hack on both.

CHDK supports the EOS M3 and M10 because they are built on the P&S codebase, while Magic Lantern does not support them.

There are signs Canon is moving to a unified codebase (likely motivated by the same market changes) in Digic 8 cameras, which may preclude CHDK as we currently know it.

However, with millions of CHDK capable P&S in circulation, there will still be potential uses for a long time to come.

Separate from smartphones, the rise of things like Rasbperry Pi, dedicated UAV and action cameras etc. have reduced cases where a hacked P&S is a clear win over other options.

In 2008, if you wanted a programmable, multi-megapixel camera with decent optics your choices were very limited and mostly expensive.

In 2019, you have a lot of options other than CHDK, but at the same time, a lot of these things can work well with CHDK too.

I think the collapse of P&S has also affected the pool of potential CHDK contributors: in 2008, a developer with a casual interest in photography would have a P&S, while today they would be more likely to have a smartphone. Someone who wants to tinker with camera software also has a lot more choices.

Could CHDK benefit from the current boom in single board computers and single board microcontrollers, like Arduino, Raspberry Pi, Esp32, Beaglebone, etc? Could those boards add even more functionality to CHDK? How?

waterwingz: Actually, there are quite a few successful projects out there using those little computers to control one or more Canon PowerShots running CHDK.

Basically anything that will support the necessary USB functionality to implement the PTP protocol and the CHDK extensions to the protocol. Applications like bookscanners, remote timelapse capture, photobooths, and multiple camera 3D image scanning.

Here is an example of Arduino and CHDK usage, with a nice PTP GUI.

reyalp: The webcams on this site are based Raspberry Pi’s using chdkptp to control CHDK cameras (chdkptp is a tool which I maintain that allows controlling CHDK cameras over USB from Linux and Windows).

One of the firsts tests with a full rig (72 cameras) shooting at same time. By nafraf, licensed under CC BY-NC 2.0.

A simple test to show the detail of a segment of the rig, how the cameras were mounted and their response after sending the turn off command using chdkptp. By nafraf, licensed under CC BY-NC 2.0.

Do you developers have time to play with CHDK? What are your preferred use?

waterwingz: There are a ton of features in CHDK and I’ve had fun playing with most of them. But for me, it’s mostly about Lua scripting when I’m actually using CHDK.

blackhole: Unfortunately my real life does not allow me to play with CHDK as much as I want.

My favorite use is when popularizing astronomy among children. It is a priceless experience when you see the glow in their eyes when they see the image of the planet they have taken themselves. For me, this is the highest value of CHDK.

reyalp: I use CHDK raw for general shooting, and scripts to do timelapse.

I’ve used motion detection for lightning and fireworks.

I also do some lo-fi astrophotography using CHDK scripts to take lots of exposures to guide and stack in software.

But what I do most is take test shots of my desk while working on the code ;)

When did you joined CHDK as a developer? Why? What is your background? What is your role?

waterwingz: July 2010 according to the records on the CHDK forum. But it seems like it was only nine years ago.

I got started because it combined two of my hobbies - computers and cameras.

Since then I’ve ported several cameras, contributed some original code, helped fix some bugs, coded many scripts, written a lot of documentation on the wiki, and helped a few newbies on the CHDK forum.

philmoz: I started with the G12 port in November 2010.

I’ve been a software developer for nearly 40 years and like waterwingz, photography is a hobby. CHDK looked like fun and I wanted something to keep me programming - my day job was more management than development.

I was pretty active until 2016, when real-life got in the way.

I now do mobile app development full time, so don’t spend much time on CHDK coding these days.

blackhole: I joined in August 2010.

Prior to that I was just reading the forum as a guest and using CHDK on the old A530 and A590 cameras. At that time I was looking for a better solution for cheap-modified webcams, which were then popular in amateur astronomy. The logical solution was to switch to something cheap with a CCD sensor, so the decision fell on Canon cameras and CHDK.

I became interested in the programming, so I started to collect knowledge on the forum and in the end I made my first port.

reyalp: Around 2008, I happened to get a Canon A540 and google “firmware hack” or something like that just for kicks. I had a background in C and assembly, and a somewhat neglected interest in photography going back to film days, so it seemed like a fun thing to play with.

For me, CHDK development was a nice change of pace, a throwback to the early PC days where if you want to draw something, you write directly to video memory instead of going through a bunch of APIs.

As people came and went from the project I somehow ended up being the chief cat herder.

nafraf: I started in June 2012. My first port was A810. I was using CHDK for a multi camera project and it was difficult to find ports of recent cameras.

With CHDK, the exposure time and ISO values can change in 1/96 EV steps. The first part of this video was made using a standard timer with exposure changes of 1/3 EV steps. The second part was made using script isoinc.lua, no post-processing. By c_joerg, licensed under CC BY-NC 2.0.

Is there anything that you would like to add?

waterwingz: Getting involved in CHDK is a bit of a trap. Once you get in, your free time just disappears. But it can be a lot of fun!

philmoz: The people who have worked on CHDK over the years are an amazingly talented, fun, and helpful group. I have learned a lot from this project and really appreciate the willingness to help, and assistance I’ve received.

reyalp: I’d like to thank all the people who have contributed over the years, and Canon for turning a blind eye to it for so long.

blackhole: CHDK is a very fun and creative project. I invite all photographers and programmers to join us and express their creativity through this project and share their experiences with us. In the end, I would like to thank the entire CHDK community for a pleasant companionship for the last ten years.

nafraf: Thanks to all people involved with this project. I have learned a lot during these years.

This video was created by changing the zoom levels between 24mm and 1200mm (35mm). For each zoom level, 2 images were taken at a time. The camera was a Canon SX50 with 200 zoom levels and CHDK. A special script was used. By c_joerg, licensed under CC BY-NC 2.0.

Thank You CHDK devs!

I want to thank CHDK devs again for taking the time and being patient enough to chat with us, as well as sharing images of their CHDK use!

I also want to thank CHDK users Garry George, Peter Laudanski, Andrew Hazelden, c_joerg, and keoeeit for having kindly shared some images and answered questions about how they shoot them!

Finally, I want to thank Pixls members paperdigits and afre for their invaluable support, without which this interview wouldn’t have been possible.

The CHDK community gathers around https://chdk.setepontos.com/ and all official CHDK documentation can be found on http://chdk.wikia.com/wiki/CHDK.

Libre Graphics Meeting 2019

Let's participate!

It’s that time of year again: Libre Graphics Meeting 2019 is fast approaching!

This year the meeting will be May 29 to June 2 in Saarbrücken, Germany. This is extra exciting because Saarbrücken is centrally located enough that we should have a nice representation from projects and community members. Members of both RawTherapee and darktable live nearby and will be in attendance (along with others from those projects and many others).

Participate!

I’m hoping to have a good representation this year, so first and foremost - please, please consider participating by giving a presentation, leading a workshop, or even a quick lightning talk! The Call for Participation page is here:

https://libregraphicsmeeting.org/2019/call-for-participation/

I will make myself available to help in any way I can. If you want a hand with the presentation, design, graphics or whatever please feel free to ping me (also - remember that we try to archive all of our presentations and material in our Github repo so you can grab any of the assets from there as well)! This is a great opportunity to spread the word about what we’re up to and the many, many awesome projects everyone has created, maintained, and contributed to for Free Software photography.

The deadline for submittal is coming up on January 15^th!
If you think you’d like to present or host a workshop please submit as soon as possible.

Cheers!

I am particularly excited about this meeting because a) I don’t get to attend every year so this is the first time I’m able to make it in a few years, and b) this is a great opportunity to really get a bunch of community members to come together! Saarbrücken is on the high-speed rail network so it’s readily accessible from many places (now you have less excuses to not make it).

I love hanging out with y’all. It’s great to nerd out about photography and catch up. Sometimes it really helps to be able to speak face-to-face and this is the perfect opportunity to also be exposed to all manner of other Free Software projects (or to expose ourselves to others?).

Besides, how else am I going to capture some fun photos of y’all?

What’s Going On

We have a few things planned for sure at the meeting and you’re going to be really sad if you miss them by not coming!

1. PIXLS.US BoF (Birds of a Feather)
   This is a special session set aside for a couple of hours for the entire community to get together and chat about what’s going on, what we’d like to do, and what’s coming up.
2. Photowalk
   I’ve been doing photowalks every year that I’ve been because this is almost the ultimate way for me to spend time with folks (unless we can do a beer drinking photowalk all at the same time…).
3. PIXLS.US Presentation/Update
   I’ll (We’ll? Anyone from the community is more than welcome to help me present on this) present on the community and what we’ve done so far and what we’d like to accomplish moving forward. This is our primary way of reporting out to the wider community who we are and what we’re doing.
4. State of the LGM
   This is a couple of slides that are included at the beginning of the program giving an overview of the state of the entire libre graphics ecosystem.

I really, really, really want to be able to add to this list with other presentations (or lightning talks, etc) that the community will give! I may even submit a couple of presentations to talk not just about the community but maybe about our technical work coordinating the forum and providing services for the projects (as well as invite other related projects to come join us).

We can make this an incredible and memorable meeting with a fantastic opportunity to meet friends in person and have a wonderful time!

Goodbye Google Analytics

A little less tracking for the new year

Over on my personal website I decided to stop using third party trackers and assets to keep from exposing visitors to unintended tracking. Third party assets expose a user to being tracked and analyzed by those third (or fourth, or more) parties and honestly this is something the web could use a little (lot) less of. I loved having stats early on when we started this crazy idea for a community and as I mentioned on my blog post, it’s a Faustian bargain to get stats at the expense of allowing Google to track what all the users of the site are doing. No thanks.

I figure it’s the eve of a new year so why not start it out right and reduce the tracking footprint of the site?

This all started by noticing that some new browser feature strips referer information from requests (thanks @darix) and we were using them to target specific areas of websites that we manage comments for. It came to my attention when I was reading the release announcement for digiKam 6.0.0 beta 3.

While fixing that problem, I found that once we fixed the referer requirement problem I was still seeing issues with Privacy Badger blocking our embed code. On further inspection it boiled down to using Google Analytics on our base domain (pixls.us) and having a cookie set by Google, which then got sent with embed requests from other websites (digiKam and darktable). This triggered the heuristic blocking by Privacy Badger.

Honestly, we derive very little value from the analytics for the price (privacy) we pay to use it. Better to simply remove it.

We still do analytics but we own the stack ourselves (thank you so much andabata!). If you want to block our own analytics the domain is: piwik.pixls.us.

2018 PlayRaw Calendar

Chris creates a new calendar for the community

Last year I got an amazing surprise in the mail. It was an awesome calendar of a handpicked selection of results from the years PlayRaw images.

Chris (@chris) put together another fantastic calendar for this year (while juggling kids, too) and it’s too nice to not have a post about it!

It was a really awesome surprise to recieve my calendar last year - and I wish I would have planned a little better to be able to grab a photo of the calendar hanging in my office (it’s my work desk calendar - it never fails to remind me that there’s more fun things to life than work - also that I need to up my processing game… ).

This year Chris has done it again by assembling a wonderfully curated collection of images and edits from the various Play Raws that were posted this year. I’ve plagiarized his post on the forums to put together this post and get some more publicity for his time and effort!

If you get a moment, please thank Chris for his work putting this together!

You can download the PDF: 2018 Play Raw Calendar

Here are the images he chose for the calendar and the edits he included:

month	image title	photographer	editor	license
0	Monkey Business	jinxos	andrayverysame	CC BY-SA
1	Glaciers, Birds, and Seals at Jökulsárlón/Iceland	BayerSe	McCap	CC BY-NC-SA
2	Shooting Into the Sun	davidvj	Adlatus	CC BY-SA
3	The Rail Bridge, North Queensferry	Brian_Innes	Jean-Marc_Digne	CC BY-SA
4	Sunset sea	Thanatomanic	sls141	CC BY-NC-SA
5	Vulcan stone sunset	asn	kazah7	CC BY-NC-SA
6	Venise la sérénissime	sguyader	Thomas_Do	CC BY-NC-SA
7	Dockland side view at night	gRuGo	CriticalConundrum	CC BY-NC-SA
8	Eating cicchetti with ghosts in Venezia	sguyader	msd	CC BY-NC-SA
9	maritime museum	wiegemalt	yteaot	CC BY-SA
10	Alfred’s Vision	jinxos	msd	CC BY-SA
11	Crescent Moon through silhouetted fern fronds	martin.scharnke	gRuGo	CC BY-NC-SA
12	Everything frozen	asn	McCap	CC BY-NC-SA

A preview (also shamelessly lifted from Chris’s forum post):

These Play Raws are a ton of fun and one of the great aspects of having such a generous community to share the images and allowing everyone to practice and play. I am constantly humbled by the amazing work our community produces and shares with everyone.

Thank you to everyone who shared image and participated in processing (and sharing how you achieved your results)! I have really learned some neat things based on others work and look forward to even more opportunities to play (pun intended).

Fun side note: the Play Raws are actually something that began on the old RawTherapee forums. When they moved their official forums here with us it was one of those awesome things I’m glad they brought over with them (the people were pretty great too… :)).

Giving More Thanks

For an awesome community

It is a yearly tradition for us to post something giving thanks around this holiday. I think it’s because this community has become such a large part of our lives. Also, I think it helps to remind ourselves once in a while of the good things that happen to us. So in that spirit…

Financial Supporters

We are lucky enough (for now) to not have huge costs, but they are costs none-the-less. We have been very fortunate that so many of you have stepped up to help pay those costs.

The Goliath of Givers

For the last several years, Dimitrios Psychogios has graciously covered our server expenses (and then some). On behalf of the community, thank you so much! You keep the servers up and running. Your generosity will cover infrastructure costs for the year and give us room to grow as the community does.

We also have some awesome folks who support us through monthly donations (which are nice because we can plan better if we need to). Together they cover the costs of data storage + transfer in/out of Amazon AWS S3 storage (basically the storage and transfer of all of the attachments and files in the forums). So thank you, you cool friends, you make the cogs turn:

• Jonas Wagner
• elGordo
• Chris
• Christian
• Claes
• Thias
• Stephan Vidi
• ukbanko
• Bill Z
• Damon Hudac
• Luka Stojanovic (a multi-year contributor!)
• Moises Mata
• WoodShop Artisans
• Barrie Minney (He’s a long time monthly contributor!)
• Mica

It is so amazing not to have to worry about finding the capital to support our growing community; we just expand things as necessary. It is super great.

If you’d like to join them in supporting the site financially, check out the support page.

Growth

As of today, we have 3135 users, so we’ve continued to grow at a very good rate! Welcome to all the new users.

As you can see from our discuss stats, we’re approaching 500k page views per month:

And our yearly community health is very positive:

gPhoto

This year we added the gphoto project to our list of supported applications! gPhoto is an awesome library for interfacing with your camera. It is used by darktable and entangle to allow you to shoot with your camera attached to your laptop or other device. We’re thrilled that they’ve joined us on the forums!

Natron

Natron is a compositing application mostly used in 3D/video compositing. The main developer was looking to give the project more of a community focus, so of course we were happy to provide them their own spot in the forum for their users to communicate and collaborate.

darix

For another year, @darix continues to keep our stuff up and running! Do you ever notice outages? No?! Me either, and that is due to his daily diligence. We can’t thank him enough for his dedication to our community.

patdavid or Pat David

The originator of it all, thank you for the initial push to create this community where we are not divided by which application we use. And for your continued good will towards everyone here, your welcoming spirit, and passion. We’d never have done it without you! And for all the great things to come!

All of You

The community is the sum of parts + all the extra love that comes from all of you! Thank you so much continuing to stick around, share you knowledge, and spread the great community. It keeps me motivated, creative, and challenged and for that I am very thankful.

Create lens calibration data for lensfun

Adding support for your lens

[Article updated on: 2019-12-09]

Introduction

All photographic lenses have several types of errors. Three of them can be corrected by software almost losslessly: distortion, transverse chromatic aberration (TCA), and vignetting. The Lensfun library provides code to do these corrections. Lensfun is not used by the photographer directly. Instead, it is used by a photo raw development software such as darktable or RawTherapee. For example, if you import a RAW into darktable, darktable detects the lens model, focal length, aperture and focal distance used for the picture, and it then calls Lensfun to automatically correct the photograph.

Lensfun uses a database to know all the parameters needed to do the lens corrections. This database is filled by photographers like you, who took time to calibrate their lenses and to submit their findings back to the Lensfun project. If you’re lucky, your lens models are already included. If not, please use this tutorial to do the calibration and contribute your results.

Let us assume your lens isn’t covered by Lensfun yet, or the corrections are either not good enough or incomplete. The following sections will explain how to take pictures for calibration. It will also show you how to create an entry of your own. The best is to provide information for all three errors but maybe you only need distortion then this is fine too.

Checking if your lens is already supported

Before you start to calibrate new lenses or report missing cameras please check the lens database first! The list is updated daily. If your lens is already support then everything is fine and you just have to update your database.

If the lens is not supported or doesn’t provide all corrections you could add the missing data following this tutorial.

Taking pictures

Before we start you need to take a lot of images for the three errors we are able to correct. This section will explain how to take them and what you need to pay attention to.

For all pictures you should use a tripod, turn off all image correction and disable image stabilization in the camera and in the lens itself! Also make sure to that all High Dynamic Range (HDR) or Dynamic Range Optimizer (DRO) features are turned off. All those options could mess up your calibration.

Distortion

For distortion you can to take pictures of a building with several parallel straight lines. You need at least two lines, one should be at the top of the image (Nearly touching the top of frame) and the other line at about a third down from the first line. The following example demonstrates this.

The lines must be perfectly straight and aligned. You can twist and rotate the camera, but the lines must have no imperfections. Common mistakes are using tiles or bricks: to your eye they may be “straight”, but it will cause calibration defects. The best buildings turn out to be parking houses (US: parking lot, EN: garages, car parks) or modern glass buildings like fruit-technology stores.

For a fixed focal length lens, you only will require one image. For a zoom lens it is recommended to take 5 to N pictures where N is max focal length minus min focal length. You must take an image at the minimum focal length, and the maximum focal length. You can move (step backward on forward) between shots to keep the 1/3rd rule above consistent.

You should shoot at your lenses sharpest aperture - this is often f/8 to f/11. Setup your camera on a tripod. Shoot at the lowest ISO (without extended values). This will be 100 or 200. Disable any inbody lens corrections. Every vendor has a different name for this process (Fuji is modular lens optimization for example). Check your camera manual and menus.

Chromatic aberrations (TCA)

For TCA images look for a large object with sharp high-contrast edges throughout the image. Preferably, the edges should be black–white but anything close to that is sufficient. Make sure that you have hard edges from the center throughout to one of the edges. The best buildings, for taking photos, have dark windows with white or gray frames.

Here are some example pictures:

You should take your pictures being at least 8 meters away. For zoom lenses, take pictures at the same focal lengths as for distortion (5 to N). Make sure to capture really sharp photos using at least f/8. The best is to use aperture control, f/8 and ISO 100 on a tripod to avoid any color noise.

You can use e.g. a streetview service to find the right building in your town (big buildings, dark windows with white or grey frames).

Vignetting

To create pictures for vignetting you need a diffuser in front of the lens. This may be translucent milk glass, or white plastic foil on glass. Whatever, as long as it is opaque enough so that nothing can be seen through it, yet transparent enough so that light can pass through it. It must not be thicker than 3 mm and shouldn’t have a noticeable texture. It must be perfectly flush with the lens front, and it mustn’t be bent. It must be illuminated homogeneously.

I ordered a piece of acryl glass, opal white (milky), smoothly polished, 78% translucency, 3mm thick, 20 x 20 cm, which is about 8 Euro on Amazon.

However white plastic foil taped on a piece of ordinary glass for stability might be enough, if the plastic doesn’t have any texture.

I normally wait for a cloudy day with no sun, then the sky is homogeneously lit. Put the camera on a tripod and point it to the sky. Put the glass directly on the lens (remove any filters). In some places where sunlight is different you may need to shoot indoors. You should experiment to make sure your images are evenly lit (except for vignetting obviously).

Make sure that no corrections are applied by the camera (some models do this even for RAWs). Set the camera to aperture priority and the lowest real ISO (this is normally 100 or 200, don’t use extended ISO values).

Switch to manual focus and focus to infinity. This is the most critical step!

For zoom lenses, you need to take pictures at five different focal lengths. You only need pictures for five focal lengths because for the other steps it gets interpolated. For a prime lens you need to take only pictures for the single focal length.

Take the pictures as RAW at the fastest aperture (e.g. f/2.8) and at three more closed apertures at 1 EV distance, and also at the most closed aperture (e.g. f/22.0). These are often marked on your lens’ aperture ring, or on your electronic display.

If you have for example a 16-35mm lens with aperture f/2.8 - f/22, you need to take pictures at 16mm, 20mm, 24mm, 28mm and 35mm focal length (Remember you require the min and max zoom values). For each for those focal lengths you need to take five pictures at f/2.8, f/4.0, f/5.6, f/8.0 and f/22.0. This makes 25 pictures in total.

For a 50mm prime lens with f/1.4 - f/16 you need to take 5 pictures at f1.4, f/2.0, f/2.8, f/4.0, and f/16.0.

**Exposing the picture correctly

For taking the picture the middle of the area needs to be as bright as possible, but not overexposed. This can be easily +1.7 to +2.0 EV.

If your camera has a zebra setting, turn it on and set the zebra mode to ‘100’. If you start to see the zebra, then take the picure. The profile is created on a RAW file and the zebra is shown for a developed picture. So we aren’t overexposed yet. In the control mode in my camera which shows overexposure everything was fine.

Vignetting correction for the professionals

The following steps are to get really fine grained vignetting corrections. The gain in accuracy is really very small! I probably only makes sense for prime lenses used for portrait or macro photography. However this is not required, the above it absolutely enough.

Lensfun is able to correct vignetting depending on focal distance. Thus, you can achieve a bit more accuracy by shooting at different focal distances. This means you will have to take pictures at 4 different focal distances.

The first focus on the near point (The near point is the closest distance that can be brought in focus). The next focal distances are the near point multiplied by 2 and by 6 and finally focus at infinity.

Example: For a 85mm prime lens with the near point at 0.8 m. You have to take pictures at 0.8 m, 1.6 m, 4.8 m and infinity.

Create calibration data

There are two ways to perform the calibration.

Lensfun allows an upload of data to the project, and they’ll do the program work for you. They’ll also review your images to make sure they are correctly taken.

Or you can do it yourself with the lens calibration script from the lensfun project.

The script needs the following dependencies to be installed on your system:

• python3
• python3-exiv2 (py3exiv2 >= 0.2.1)
• python3-numpy
• python3-scipy
• darktable-cli (darktable >= 2.4.0)
• tca_correct (hugin >= 2018)
• convert (ImageMagick)

You can download the lens calibration script HERE or get it as a package for the major distributions HERE.

Once you have downloaded the tool create a folder for your lens calibration data, change to the directory and run:

$ lens_calibrate.py init
The following directory structure has been created in the local directory

1. distortion - Put RAW file created for distortion in here
2. tca        - Put chromatic abbreviation RAW files in here
3. vignetting - Put RAW files to calculate vignetting in here

Follow the instructions and copy your raw files in the corresponding directories.

Vignetting correction for the professionals

For each focal distance you captures pictures you have to create a folder.

Lets pick up the example from above. For a 85mm prime lens we took pictures at 0.8 m, 1.6 m, 4.8 m and infinity. For this lens you would have to create the following folder structure in the vignetting directory:

vignetting/0.8
vignetting/1.6
vignetting/4.8
vignetting/inf

The folder inf is for the focal distance at infinity.

Distortion

Once you copied the files in place it is time to generate the pictures (tif files) for distortion calculations. You can do this with the ‘distortion’ option:

$ lens_calibrate.py distortion
Running distortion corrections ...
Converting distortion/_7M32376.ARW to distortion/exported/_7M32376.tif ... DONE
A template has been created for distortion corrections as lenses.conf.

Once the tif files has been created, you can start Hugin.

Torsten Bronger created a screen cast to give an overview about the distortion process in Hugin. He uses an old Hugin version in the video. The following section of this tutorial explains how to do it with Hugin 2018. You can watch the screen cast first if you want, you can do it here (Vimeo).

If you start Hugin the first time, the windows you will get should look like in Figure 8.

First select on the menu bar Interface -> Expert to switch to the Expert mode. You will get a windows which should look like as in Figure 9.

Once in the export mode click on Add images (Figure 10) and load the first tiff from the distortion/exported folder.

By default the lens type should be set to Normal (rectiliniar) for normal standard lenses. Make sure that the focal length is correct and set the Focal length multiplier, which is the crop factor of your camera. For full frame bodies this value should be 1. If you have a crop camera you need to set the correct crop value you can find in the specifications. Next click on the Control Points tab (Figure 11).

This is the tab to set the control points so that we can tell the software what are our straight lines we are interested in. In this tab you have to make sure that auto fine-tune is disabled, auto add is enabled and auto-estimate is disabled! If this is the case zoom the image to 200% (you can also do this by pressing ‘2’ on the keyboard).

In the zoomed images you have start at the top edges. On the left go to the top left corner and to the top right corner on the right. The first straight line, from left to right, should be visible. Select the first control point on the left edge of the picture on the left page and the right edge on the right (Figure 12).

IMPORTANT: Once you have the first control point selected in both images. Select Add new Line in the mode dropdown menu! This will add the two control points as line 3! Now continue adding corresponding control points in both pictures till you’re in the middle on both sides.

Tip: The easiest and fasted is to set control points in the middle at the tiling line. This reduces the required mouse movements.

Now zoom out by pressing ‘0’ and check it if everything has been added correctly (Figure 13).

While you are zoomed out, find a line which is about 3rd into the image from the top to repeat adding a line. Zoom to 200% again, select the first control points and again Add a new line which will result in line4 (Figure 14)!

Zoom out by pressing ‘0’ and check that you have two lines, line3 and line4. Now move on to the Stitcher tab (Figure 14).

In the Stitcher tab you need to select the correct Projection for your lens. This is Rectilinear for standard lenses. Once done switch to the Photos tab (Figure 16).

At the bottom under Optimize select Custom parameters for Geometric. This will add an Optimizer tab. Switch to it once it appears (Figure 17).

Select the ‘a’, ‘b’ and ‘c’ lens parameters and click on Optimize now!. Accept the calculation with yes. Now the values for ‘a’, ‘b’ and ‘c’ will change (Figure 18).

The calculated correction values for ‘a’, ‘b’ and ‘c’ you can find in the tab need to be added to the lenses.conf. Open The file and fill out the missing options. Here is an example:

Example:

[FE 85mm F1.4 GM]
maker = Sony
mount = Sony E
cropfactor = 1.0
aspect_ratio = 3:2
type = normal

• maker is should be the lens manufacturer e.g. Sony
• mount is the mount system for the lens, check the lensfun database
• cropfactor is 1.0 for full frame cameras, if you have a crop camera find out the correct crop factor for it.
• aspect_ratio is the aspect ratio for the pictures which is normally 3:2.
• type is the type of the lens, e.g. ‘normal’ for standard rectilinear lenses. Other values are: stereographic, equisolid, stereographic, panoramic or fisheye.

If you have e.g. a 85mm there should be an entry for the focal length which is set to: 0.0, 0.0, 0.0. You need to change the values in the lenses.conf for your focal length with the calculated corrections from the Optimizer tab (Figure 16).

[FE 85mm F1.4 GM]
maker = Sony
mount = Sony E
cropfactor = 1.0
aspect_ratio = 3:2
type = normal
distortion(85mm) = 0.002, 0.001, -0.009

But I don’t want to do distortion corrections!

No problem, if you want to skip this step then you can created the lenses.conf manually. It should look like the following example:

[lens model]
maker =
mount =
cropfactor = 1.0
aspect_ratio = 3:2
type = normal

The section name is the lens model. You can find it out by running:

exiv2 -g LensModel -pt <raw image file>

The other options are:

• maker is should be the lens manufacturer e.g. Sony
• mount is the mount system for the lens, check the lensfun database
• cropfactor is 1.0 for full frame cameras, if you have a crop camera find out the correct crop factor for it.
• aspect_ratio is the aspect ratio for the pictures which is normally 3:2.
• type is the type of the lens, e.g. ‘normal’ for standard rectilinear lenses. Other values are: stereographic, equisolid, stereographic, panoramic or fisheye.

TCA

You can skip this step if you don’t want to do TCA corrections.

This step is fully automatic, all you have to do is to run the following command and wait:

$ lens_calibrate tca
Running TCA corrections for tca/exported/_7M32375.ppm ... DONE

However it possible to calculate more complex TCA corrections. For this you need to run the step it with an additional command line argument, like this:

$ lens_calibrate --complex-tca tca
Running TCA corrections for tca/exported/_7M32375.ppm ... DONE

Vignetting

You can skip this step if you don’t want to do vignetting corrections.

To calculate the vignetting corrections it is also a very simple step. All you have to do is to run the following command and wait:

$ lens_calibrate vignetting

Generating the XML

To get corrections for lensfun you need a lenses.conf with the required options to be filled out (maker, mount, cropfactor, aspect_ratio, type). And at least one of the corrections steps done. If you have this you can generate the XML file which can be consumed by lensfun. You can do it with the following command:

$ lens_calibrate generate_xml
Generating lensfun.xml

You can redo this step as many times as you want. And you can just rerun it if you add an additional correction.

Using the lensfun.xml

You may want to fine-tune the lens model name in the generated lensfun.xml file. Lensfun normalises names before any matching, so you have some freedom. For example, upper/lowercase can be changed arbitrarily. Any single f is ignored, so you may change 16-35mm 2.8 into 16-35mm f/2.8. If there was a tele converter involved, you must add “converter” into the name so that Lensfun does not try to derive allowed focal lengths from the lens name. Ordering of parts in the lens name is completely unimportant for matching. As are single punctuation characters. You may even add things (e.g. 16-35 into 16-35mm) but be conservative here. Never drop anything what exiv2 reports!

If you want to use the generated lensfun.xml file to test if the calibration you created works, you can copy to the local lensfun config folder in your home directory.

cp lensfun.xml ~/.local/share/lensfun

Make sure your camera is recognized by lensfun or you need to add an entry to the lensfun.xml file too.

Contributing your lensfun.xml

To contribute your calibration data data for your lens to the lensfun project, execute the script with the following command:

$ lens_calibrate ship
Created lensfun_calibration.tar.xz
Open a bug at https://github.com/lensfun/lensfun/issues/ with the data.

This will create a tarball with all the required data. Now go to

• https://github.com/lensfun/lensfun/issues/

and open a bug using the following subject:

Calibration data for <lens model>

And for the description just use:

Please add the attached lens data to the lensfun data base.

Attach the lensfun_calibration.tar.xz to the bugreport.

Feedback

Feedback for this article is very welcome. If you’re a lensfun developer and read this please contact me. I would like to contribute the script to lensfun and further improve the article. I still have unanswered questions.

Support Andrea Ferrero on Patreon!

Andrea is developing Photo Flow, GIMP AppImage, Hugin AppImage, and more!

Andrea Ferrero, or as we know him Carmelo_DrRaw, has been contributing to the PIXLS.US community since April of 2015. A self described developer and photography enthusiast, Andrea is the developer of the PhotoFlow image editor, and is producing AppImages for:

• The GIMP image manipulation program - weekly AppImage packages from stable releases and development branches.
• The RawTherapee editor - nightly AppImage and Windows packages from stable and development branches
• LuminanceHDR - nightly AppImage packages for Linux
• HDRMerge - nightly AppImage packages for Linux
• The Hugin panorama photo stitcher - AppImages for stable releases and development branches

Andrea is the best sort of community member, contributing six different projects (including his own)! He is always thoughtful in his responses, does his own support for PhotoFlow, and is kind and giving. He has finally started a Patreon page to support his all of his hard work. Support him now!

He was also kind enough to answer a few questions for us:

PX: When did you get into photography? What’s your favorite subject matter?

AF: I think I was about 15 when I got my first reflex, and I was immediately fascinated by macro-photography. This is still what I like to do the most, together with taking pictures of my kids. ;-) By the way, you can visit my personal free web gallery on GitHub: http://aferrero2707.github.io/photorama/gallery/ (adapted from this project).

It is still a work in progress, but you are welcome to fork it and adapt it to your needs if you find it useful!

PX: What brought you to using and developing Free/Open Source Software?

AF: I started to get interested in programming when I was at the university, in the late 90’s. At that time I quickly realized that the easiest way to write and compile my code was to throw Linux into my hard drive. Things were not as easy as today but I eventually managed to get it running, and the adventure began.

A bit later I started a scientific career (nothing related to image processing or photography, so I won’t bother with more details about my daily job), and since then I have been a user of Linux-based computing clusters for almost 20 years at the time of writing… A large majority of the software tools I use at work are free and open sourced and this definitely has marked my way of thinking and developing.

PX: What are some new/exciting features you develop in Photo Flow?

AF: Currently I am mostly focusing on HDR processing and high-quality Dynamic Range compression - what is also commonly called shadows/highlights compression.

More generally, there is still a lot of work to do on the performances side. The software is already usable and quite stable, but some of the image filters are still a bit too slow for real-time feedback, especially when combined together.

The image exporting module is also currently in a state of work in progress. It is already possible to select either Jpeg or TIFF (8, 16 or floating-point 32 bits bit depth) as the output format, to resize the image and add some post-resize sharpening, and to select the output ICC profile. What is still missing is a real-time preview of the final result, with a possibility to soft-proof the output profile. The same options need to be included in the batch processor as well.

On a longer term, and if there is some interest from the community, I am thinking about porting the code to Android in a simplified form that would be suitable for tablets and the like. The small memory footprint of the program could be an important advantage on such systems.

PX: What other applications would you like to make an AppImage for? Have you explored Snaps or Flatpaks?

AF: I am currently developing and refining AppImage packages for GIMP, RawTherapee, LuminanceHDR and HDRMerge, in addition to PhotoFlow. All packages are automatically built and deployed through Travis CI, for better reproducibility and increased security. Hugin is the next application that I plan to package as an AppImage.

All the AppImage projects are freely available on GitHub. That’s also the best place for any feedback, bug report, or suggestion.

There is an ongoing discussion with the GIMP developers about the possibility to provide the AppImage as an official download.

In addition to the AppImage packages, I am also working with the RawTherapee developers on cross-compiled Windows packages that are also automatically built on Travis CI. The goal is to help them provide up-to-date packages from the main development branches, so that more users can test them and provide feedback.

I’m also open to any suggestions for additional programs that could be packaged as AppImages, so do not hesitate to express your wishes!

Personally I am a big fan of the AppImage idea, mostly because, unlike Snap or Flatpack packages, it is not bound to any specific distribution or run-time environment. The packager has full control over the contents of the AppImage package, pretty much like MacOS bundles.

Moreover, I find the community of developers around the AppImage format very active and open-minded. I am currently collaborating to improve the packaging of GTK applications. For those who are interested in the details, the discussion can be followed here: https://github.com/linuxdeploy/linuxdeploy/issues/2

G'MIC 2.3.6

10 Years of Open Source Image Processing!

The IMAGE team of the GREYC laboratory is happy to celebrate the 10th anniversary of G’MIC with you, an open-source (CeCILL), generic and extensible framework for image processing. GREYC is a public research laboratory on digital technology located in Caen, Normandy/France, under the supervision of 3 research institutions: the CNRS (UMR 6072), the University of Caen Normandy and the ENSICAEN engineering school.

This celebration gives us the perfect opportunity to announce the release of a new version (2.3.6) of this free software and to share with you a summary of the latest notable changes since our last G’MIC report, published on PIXLS.US in February 2018.

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Related links:

• The G’MIC project
• Twitter feed
• Announcement of the first version of G’MIC on LinuxFr.org [fr]
• Previous article about G’MIC on PIXLS.US

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(Click on the images of the report to display them in full resolution)

1. Looking back at 10 years of development

G’MIC is a multiplatform framework (GNU/Linux, macOS, Windows…) providing various user interfaces for manipulating generic image data, such as 2D or 3D hyperspectral images or image sequences with float values (thus including “normal” color images). More than 1000 different operators for image processing are included, a number that is extensible at will since users can add their own functions by using the embedded script language.

It was at the end of July 2008 that the first lines of G’MIC code were created (in C++). At that time, I was the main developer involved in CImg, a lightweight open source C++ library for image processing, when I made the following observation:

• The initial goal of CImg, which was to propose a “minimal” library of functions to help C++ developers to develop image processing algorithms, was broadly achieved; most of the algorithms I considered as essential in image processing were integrated. CImg was initially meant to stay lightweight, so I didn’t want to include new algorithms ad vitam æternam, which would be too heavy or too specific, thus betraying the initial concept of the library.
• However, this would only cater to a rather small community of people with both C++ knowledge and image processing knowledge! One of the natural evolutions of the project, creating bindings of CImg to other programming languages, didn’t appeal much to me given the lack of interest I had in writing the code. And these potential bindings still only concerned an audience with some development expertise.

My ideas were starting to take shape: I needed to find a way to provide CImg processing features for non-programmers. Why not attempt to build a tool that could be used on the command line (like the famous convert command from Imagemagick)? A first attempt in June 2008 (inrcast, presented on the French news site LinuxFR), while unsuccessful, allowed me to better understand what would be required for this type of tool to easily process images from the command line.

In particular, it occurred to me that conciseness and coherence of the command syntax were the two most important things to build upon. These were the aspects that required the most effort in research and development (the actual image processing features were already implemented in CImg). In the end, the focus on conciseness and coherence took me much further than originally planned as G’MIC got an interpreter) of its own scripting language, and then a JIT compiler for the evaluation of mathematical expressions and image processing algorithms working at the pixel level.

With these ideas, by the end of July 2008, I was happy to announce the first draft of G’MIC. The project was officially up and running!

A few months later, in January 2009, enriched by my previous development experience on GREYCstoration (a free tool for nonlinear image denoising and interpolation, from which a plug-in was made for GIMP), and in the hopes of reaching an even larger public, I published a G’MIC GTK plug-in for GIMP. This step proved to be a defining moment for the G’MIC project, giving it a significant boost in popularity as seen below (the project was hosted on Sourceforge at the time).

The sudden interest in the plugin from different users of GIMP (photographers, illustrators and other types of artists) was indeed a real launchpad for the project, with the rapid appearance of various contributions and external suggestions (for the code, management of the forums, web pages, writing of tutorials and realization of videos, etc.). The often idealized community effect of free software finally began to take off! Users and developers began to take a closer look at the operation of the original command-line interface and its associated scripting language (which admittedly did not interest many people until that moment!). From there, many of them took the plunge and began to implement new image processing filters in the G’MIC language, continuously integrated them into the GIMP plugin. Today, these contributions represent almost half of the filters available in the plugin.

Meanwhile, the important and repeated contributions of Sébastien Fourey, colleague of the GREYC IMAGE team (and experienced C++ developer) significantly improved the user experience of G’MIC. Sébastien is indeed at the heart of the main graphical interface development of the project, namely:

• The G’MIC Online web service (which was later re-organised by GREYC’s Development Department).
• Free Software ZArt, a graphical interface - based on the _Qt_ library - for the application of G’MIC filters to video sequences (from files or digital camera streams).
• And above all, at the end of 2016, Sébastien tackled a complete rewrite of the G’MIC plugin for GIMP in a more generic form called G’MIC-Qt. This component, also based on the _Qt_ library (as the name suggests), is a single plugin that works equally well with both GIMP and Krita, two of the leading free applications for photo retouching/editing and digital painting. G’MIC-Qt has now completely supplanted the original GTK plugin thanks to its many features: built-in filter search engine, better preview, superior interactivity, etc. Today it is the most successful interface of the G’MIC project and we hope to be able to offer it in the future for other host applications (contact us if you are interested in this subject!).

The purpose of this article is not to go into too much detail about the history of the project. Suffice it to say that we have not really had time to become bored in the last ten years!

Today, Sébastien and I are the two primary maintainers of the G’MIC project (Sébastien mainly for the interface aspects, myself for the development and improvement of filters and the core development), in addition to our main professional activity (research and teaching/supervision).

Let’s face it, managing a free project like G’MIC takes a considerable amount of time, despite its modest size (~120k lines of code). But the original goal has been achieved: thousands of non-programming users have the opportunity to freely and easily use our image processing algorithms in many different areas: image editing, photo manipulation, illustration and digital painting, video processing, scientific illustration, procedural generation, glitch art…

The milestone of 3.5 million total downloads was exceeded last year, with a current average of about 400 daily downloads from the official website (figures have been steadily declining in recent years as G’MIC is becoming more commonly downloaded and installed via alternative external sources).

It is sometimes difficult to keep a steady pace of development and the motivation that has to go with it, but we persisted, thinking back to the happy users who from time to time share their enthusiasm for the project!

Obviously we can’t name all the individual contributors to G’MIC whom we would like to thank, and with whom we’ve enjoyed exchanging during these ten years, but our heart is with them! Let’s also thank the GREYC laboratory and INS2I institute of CNRS for their strong support for this free project. A big thank you also to all the community of PIXLS.US who did a great job supporting the project (hosting the forum and publishing our articles on G’MIC).

But let’s stop reminiscing and get down to business: new features since our last article about the release of version 2.2!

2. Automatic illumination of flat-colored drawings

G’MIC recently gained a quite impressive new filter named « Illuminate 2D shape », the objective of which is to automatically add lit zones and clean shadows to flat-colored 2D drawings, in order to give a 3D appearance.

First, the user provides an object to illuminate, in the form of an image on a transparent background (typically a drawing of a character or animal). By analyzing the shape and content of the image, G’MIC then tries to deduce a concordant 3D elevation map (“ bumpmap “). The map of elevations obtained is obviously not exact, since a 2D drawing colored in solid areas does not contain explicit information about an associated 3D structure! From the estimated 3D elevations it is easy to deduce a map of normals (“ normalmap “) which is used in turn to generate an illumination layer associated with the drawing (following a Phong Shading model).

This new filter is very flexible and allows the user to have a fairly fine control over the lighting parameters (position and light source rendering type) and estimation of the 3D elevation. In addition the filter gives the artist the opportunity to rework the generated illumination layer, or even directly modify the elevation maps and estimated 3D normals. The figure below illustrates the process as a whole; using the solid colored beetle image (top left), the filter fully automatically estimates an associated 3D normal map (top right). This allows it to generate renditions based on the drawing (bottom row) with two different rendering styles: smooth and quantized.

Despite the difficulty inherent in the problem of converting a 2D image into 3D elevation information, the algorithm used is surprisingly effective in a good many cases. The estimation of the 3D elevation map obtained is sufficiently consistent to automatically generate plausible 2D drawing illuminations, as illustrated by the two examples below - obtained in just a few clicks!

It occurs, of course, that the estimated 3D elevation map does not always match what one might want. Fear not, the filter allows the user to provide “guides” in the form of an additional layer composed of colored lines, giving more precise information to the algorithm about the structure of the drawing to be analyzed. The figure below illustrates the usefulness of these guides for illuminating a drawing of a hand (top left); the automatic illumination (top right) does not account for information in the lines of the hand. Including these few lines in an additional layer of “guides” (in red, bottom left) helps the algorithm to illuminate the drawing more satisfactorily.

If we analyze more precisely the differences obtained between estimated 3D elevation maps with and without guides (illustrated below as symmetrical 3D objects), there is no comparison: we go from a very round boxing glove to a much more detailed 3D hand estimation!

Finally, note that this filter also has an interactive preview mode, allowing the user to move the light source (with the mouse) and have a preview of the drawing illuminated in real time. By modifying the position parameters of the light source, it is thus possible to obtain the type of animations below in a very short time, which gives a fairly accurate idea of the 3D structure estimated by the algorithm from the original drawing.

A video showing the various possible ways to edit the illumination allowed by this filter is visible here. The hope is this new feature of G’MIC allows artists to accelerate the illumation and shading stage of their future drawings!

3. Stereographic projection

In a completely different genre, we have also added a filter implementing stereographic projection, suitably named “Stereographic projection“. This type of cartographic projection makes it possible to project planar defined image data onto a sphere. It should be noted that this is the usual projection used to generate images of “mini-planets” from equirectangular panoramas, like the one illustrated in the figure below.

If we launch the G’MIC plugin with this panorama and select the filter “Stereographic projection“, we get:

The filter allows precise adjustments of the projection center, the rotation angle, and the radius of the sphere, all interactively displayed directly on the preview window (we will come back to this later). In a few clicks, and after applying the filter, we get the desired “mini-planet”:

It is also intruiging to note that simply by reversing the vertical axis of the images, we transform a “mini-planet” into a “max-tunnel”!

Again, we made this short video which shows this filter used in practice. Note that G’MIC already had a similar filter (called “Sphere“), which could be used for the creation of “mini-planets”, but with a type of projection less suitable than the stereographic projection now available.

4. Even more possibilities for color manipulation

Manipulating the colors of images is a recurring occupation among photographers and illustrators, and G’MIC already had several dozen filters for this particular activity - grouped in a dedicated category (the originally named “Colors“ category!). This category is still growing, with two new filters having recently appeared:

• The “CLUT from after-before layers“ filter tries to model the color transformation performed between two images. For example, suppose we have the following pair of images:

Problem: we do not remember at all how we went from the the original image to the modified image, but we would like to apply the same process to another image. Well, no more worries, call G’MIC to the rescue! The filter in question will seek to better model the modification of the colors in the form of a HaldCLUT, which happens to be a classic way to represent any colorimetric transformation.

The HaldCLUT generated by the filter can be saved and re-applied on other images, with the desired property that the application of the HaldCLUT on the original image produces the target model image originally used to learn the transformation. From there, we are able to apply an equivalent color change to any other image:

This filter makes it possible in the end to create HaldCLUT “by example”, and could therefore interest many photographers (in particular those who distribute compilations of HaldCLUT files, freely or otherwise!).

• A second color manipulation filter, named “Mixer [PCA]“ was also recently integrated into G’MIC. It acts as a classic color channel mixer, but rather than working in a predefined color space (like sRGB, HSV, Lab…), it acts on the “natural” color space of the input image, obtained by principal component analysis (PCA) of its RGB colors. Thus each image will be associated with a different color space. For example, if we take the “lion” image below and look at the distribution of its colors in the RGB cube (right image), we see that the main axis of color variation is defined by a straight line from dark orange to light beige (axis symbolized by the red arrow in the figure).

The secondary axis of variation (green arrow) goes from blue to orange, and the tertiary axis (blue arrow) from green to pink. It is these axes of variation (rather than the RGB axes) that will define the color basis used in this channel mix filter.

It would be wrong to suggest that it is always better to consider the color basis obtained by PCA for the mixing of channels, and this new filter is obviously not intended to be the “ultimate” mixer that would replace all others. It simply exists as an alternative to the usual tools for mixing color channels, an alternative whose results proved to be quite interesting in tests of several images used during the development of this filter. It does no harm to try in any case…

5. Filter mishmash

This section is about a few other filters improved or included lately in G’MIC which deserve to be talked about, without dwelling too much on them.

• Filter “Local processing” applies a color normalization or equalization process on the local image neighborhoods (with possible overlapping). This is an additional filter to make details pop up from under or over-exposed photographs, but it may create strong and unpleasant halo artefacts with non-optimal parameters.

  

• If you think that the number of layer blending modes available in GIMP or Krita is not enough, and dream about defining your own blending mode formula, then the recent improvement of the G’MIC filter « Blend [standard] » will please you! This filter now gets a new option « Custom formula » allowing the user to specify their own mathematical formula when blending two layers together. All of your blending wishes become possible!

  

• Also note the complete re-implementation of the nice “Sketch“ filter, which had existed for several years but could be a little slow on large images. The new implementation is much faster, taking advantage of multi-core processing when possible.

  

• A large amount of work has also gone into the re-implementation of the “Mandelbrot - Julia sets“ filter, since the navigation interface has been entirely redesigned, making exploration of the Mandelbrot set much more comfortable (as illustrated by this video). New options for choosing colors have also appeared.

  

• In addition, the “Polygonize [Delaunay]“ filter that generates polygonized renderings of color images has a new rendering mode, using linearly interpolated colors in the Delaunay triangles produced.

  

6. Other important highlights

6.1. Improvements of the plug-in

Of course, the new features in G’MIC are not limited to just image processing filters! For instance, a lot of work has been done on the graphical interface of the plug-in G’MIC-Qt for GIMP and Krita:

• Filters of the plug-in are now allowed to define a new parameter type point(), which displays as a small colored circle over the preview window. The user can drag this circle and move it with the mouse. As a result this can give the preview widget a completely new type of user interaction, which is no small thing! A lot of filters now use this feature, making them more pleasant to use and intuitive (look at this video for some examples). The animation below shows for instance how these new interactive points has been used in the filter « Stereographic projection » described in previous sections.

• In addition, introducing these interactive points has allowed improving the split preview modes, available in many filters to display the « before/ after » views side by side when setting the filter parameters in the plug-in. It is now possible to move this « before/ after » separator, as illustrated by the animation below. Two new splitting modes (« Checkered » and « Inverse checkered » ) have been also included alongside it.

A lot of other improvements have been made to the plug-in: the support of the most recent version of GIMP (2.10), of Qt 5.11, improved handling of the error messages displayed over the preview widget, a cleaner designed interface, and other small changes have been made under the hood, which are not necessarily visible but slightly improve the user experience (e.g. an image cache mechanism for the preview widget). In short, that’s pretty good!

6.2. Improvements in the software core

Some new refinements of the G’MIC computational core have been done recently:

• The “standard library” of the G’MIC script language was given new commands for computing the inverse hyperbolic functions (acoss, asinh and atanh), as well as a command tsp (travelling salesman problem) which estimates an acceptable solution to the well-known Travelling salesman problem, and this, for a point cloud of any size and dimension.

  

  

• The demonstration window, which appears when gmic is run without any arguments from the command line, has been also redesigned from scratch.

• The embedded JIT compiler used for the evaluation of mathematical expressions has not been left out and was given new functions to draw polygons (function polygon()) and ellipses (function ellipse()) in images. These mathematical expressions can in fact define small programs (with local variables, user-defined functions and control flow). One can for instance easily generate synthetic images from the command line, as shown by the two examples below.

Example 1

$ gmic 400,400,1,3 eval "for (k = 0, k<300, ++k, polygon(3,u([vector10(0),[w,h,w,h,w,h,0.5,255,255,255])))"

Result:

Example 2

$ gmic 400,400,1,3 eval "for (k=0, k<20, ++k, ellipse(w/2,h/2,w/2,w/8,k*360/20,0.1,255))"

Result:

• Note also that NaN values are now better managed when doing calculus in the core, meaning G’MIC maintains coherent behavior even when it has been compiled with the optimisation -ffast-math. Thus, G’MIC can be flawlessly compiled now the maximum optimization level -Ofast supported by the compiler g++, whereas we were restricted to the use of -O3 before. The improvement in computation speed is clearly visible for some of the offered filters !

6.3. Distribution channels

A lot of changes have also been made to the distribution channels used by the project:

• First of all, the project web pages (which are now using secured https connections by default) have a new image gallery. This gallery shows both filtered image results from G’MIC and the way to reproduce them (from the command line). Note that these gallery pages are automatically generated by a dedicated G’MIC script, which ensures the displayed command syntax is correct.

  

This gallery is split into several sections, depending on the type of processing done (Artistic, Black & White, Deformations, Filtering, etc.). The last section « Code sample » is my personal favorite, as it exhibits small animations (shown as looping animated GIFs) which have been completely generated from scratch by short scripts, written in the G’MIC language. Quite a surprising use of G’MIC that shows its potential for generative art.

• We have also moved the main git source repository of the project to Framagit, still keeping one synchronized mirror on Github at the same place as before (to benefit from the fact that a lot of developers have already an account on Github which makes it easier for them to fork the project and write bug reports).

7. Conclusions and Perspectives

Voilà! Our tour of news (and the last six months of work) on the G’MIC project comes to an end.

We are happy to be celebrating 10 years with the creation and evolution of this Free Software project, and to be able to share with everyone all of these advanced image processing techniques. We hope to continue doing so for many years to come!

Note that next year, we will also be celebrating the 20th anniversary of CImg, the C++ image processing library (started in November 1999) on which the G’MIC project is based, proof that interest in free software is enduring.

As we wait for the next release of G’MIC, don’t hesitate to test the current version. Freely and creatively play with and manipulate your images to your heart’s content!

Thank you, Translators: (ChameleonScales, Pat David)

From Russia with Love

An Interview with Photographer Ilya Varivchenko

Ilya Varivchenko is a fashion and portrait photographer from Ivanovo, Russian Federation. He’s a UNIX administrator with a long-time passion for photography that has now become a second part-time job for him. Working on location and in his studio, he’s been producing a wonderful body of work specializing in portraiture, model tests, and more.

He’s a member of the community here (@viv), and he was kind enough to spare some time and answer a few questions (plus it gives me a good excuse to showcase some of his great work!).

Much of your work feels very classical in posing and light, particularly your studio portraits. What would you say are your biggest influences?

I am influenced by several classical painters and great modern photographers. Some of them are: Patrick Demarchelier, Steven Meisel and Peter Lindbergh. The general mood defines what I see around me. Russia is a very neglected but beautiful country and women around are an inexhaustible source of inspiration.

How would you describe your own style overall?

My style is certainly a classic portrait in its modern performance.

What motivates you when deciding who/how you shoot?

I usually plan shooting in advance. The range of models is rather narrow and it’s not so easy to get there. However, I am constantly looking for new faces. I choose the style and direction of a particular shooting based on my vision of the model and the current mood.

Why portraits? What about portraiture draws you to it?

I shoot portraits because people interest me. For me, photography is an instrument of knowing people and a means of communication.

If you had to pick your own favorite 3 photographs of your work, which ones would you choose and why?

It’s difficult to choose only three photographs, but maybe these:

If you had to pick 3 favorite images from someone else, which ones would you choose and why?

It is very difficult to choose only three photos. The choice in any case will be incomplete, but here’s the first ones that comes to mind:

1. The portrait of Heather Stewart-Whyte by Friedemann Hauss:

2. The portrait of Monica Bellucci by Chico Bialas:

3) The portrait of Nicole Kidman by Patrick Demarchelier

How do you find your models usually?

Via social media which is the best means for model searching, but if I meet a girl I really like in the street, I can try and talk to her straight away. In fact, the problem is not to find a model, but to choose how to reject a request without offending a prospect model that is of no interest to me.

Do you pre-visualize and plan your shoots ahead of time usually, or is there a more organic interaction with the model and the space you’re shooting in?

It’s always good to have a plan. It is also very good to have a spare plan.

Usually I discuss some common points with the model and stylist before shooting. But these plans are more connected with the mood and the general idea of the session. So when the magic of shooting begins, usually all the plans fly to hell. ;)

Do you have a shooting assistant with you, or is normally just you and the model?

The preparatory stage of shooting often requires participation of many people: a makeup artist, a hair stylist, etc., but shooting itself goes better when only two persons are involved. This is a fairly intimate process. Just like sex. :)

On the other hand, if we do a fashion shoot on order, then the presence of the customer representatives is a must.

Many shots have a strong editorial fashion feel to them: are those works for magazine/editorial use - or were they personal works you were planning to be that way?

I take pictures for local magazines and advertising agencies sometimes. Maybe it somehow influenced my other work.

What do you do with the photos you shoot?

Most of my works are for personal use. However, I often print them in a large format and I’ve also had two solo exhibitions. Prints with my works are sold and they can always be ordered. I also publish in photo magazines sometimes, but these magazines are Russian ones so they are hardly known to you.

By the way: I periodically take part in the events held by Olympus Russia, where I demonstrate my workflow.

This video shows that I use the RawTherapee as a raw converter :)

You’re shooting on Olympus gear quite a bit, are you officially affiliated with Olympus in some way?

On occasions I hold workshops as a part of the Olympus company marketing activities. Sometimes the Olympus company provides me with their products for testing and I am expected to follow up with a review.

Is your choice to use Free Software for pragmatic reasons, or more idealistic?

The choice was dictated by purely practical considerations. I found a tool, the results of which I am almost completely satisfied with. Detail for example is outstanding, comfortable work with color grading, excellent black and white conversion, and much more.

The fact that the product is free and (which is more important to me) I have an opportunity to communicate with its developers is a huge plus!

For example, with the output of Fuji X-T20, when it was required to add a new DCP profile to the converter I simply contacted the developers, shot the test target and got what I wanted.

Would you describe your workflow a bit? Which projects do you use regularly?

My workflow is quite simple:

1. Shooting. I try to shoot in a way which will not require heavy postprocessing at all. It is much easier to set up light properly than to fix it in Photoshop later.

2. Raw development with RawTherapee. My goal is to develop the image in a way which makes it as close to final as possible. Sometimes this is the end of my workflow. ;)

3. Color correction (if necessary) with 3DLutCreator. In rare cases, it is more convenient to make complex color correction with the help of LUTs.

4. Retouching with Adobe Photoshop. Nothing special. Removal of skin and hair defects, etc. Dodge and burn technique with a Wacom Intuos Pro.

Speaking of gear, what are you shooting with currently?

I have two systems now: Micro Four Thirds system from Olympus and X Series from Fujifilm. Typical setups are:

Studio: Olympus PEN-F + Panasonic G 42.5/1.7 Planair: Olympus PEN-F + M.Zuiko 75/1.8 or FujiFilm X-T20 + Fujinon 35/1.4

Many of your images appear make great use of natural light. For your studio lighting setup, what type of lighting gear are you using?

My studio equipment is a mix of Aurora Codis and Bowens studio lights + a lot of modifiers from large 2 meters parabolic octobox to narrow 40x150 strip boxes and so on.

Is there something outside your comfort zone you wish you could try/shoot more of?

It is definitely landscape photography. And macro photography also attracts me - ants and snails are all great models in fact. :)

What is one piece of advice you would offer to another photographer?

Find in yourself what you want to share with others. Beauty is in the eye of the beholder. No beautiful models will help if you are empty inside.

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I want to thank Ilya for taking the time to chat with me! Take some time to have a look through his blog and work (it’s chock full of wonderful work)!

All images copyright Ilya Varivchenko and used with permission.

Welcoming the gPhoto Project to the PIXLS.US community!

Helping the community one project at a time

A major goal of the PIXLS.US effort is to do whatever we can do to help developers of projects unburden themselves from administrating their project. We do this, in part, by providing forum hosting, participating in support, providing web design, and doing community outreach. With that in mind, we are excited to welcome the gPhoto Projects to our discuss forum!

The Entangle interface, which makes use of libgphoto.

You may not have heard of gPhoto, but there is a high chance that you’ve used the project’s software. At the heart of the project is libgphoto2, a portable library that gives application access to hundreds of digital cameras. On top of the foundational library is gphoto2, a command line interface to your camera that supports almost everything that the library can do. The library is used in a bunch of awesome photography applications, such as digiKam, darktable, entangle, and GIMP. There is even a FUSE module, so you can mount your camera storage as a normal filesystem.

gPhoto was recruited to the PIXLS.US community when @darix was sitting next to gPhoto developer Marcus. Marcus was using darix’s Fuji camera to test integration into libgphoto, then the magic happened! Not only will some Fuji models be supported, but our community is growing larger. This is also a reminder that one person can make a huge difference. Thanks darix!

Welcome, gPhoto, and thank you for the years and years of development!

(NSFW) What Stefan Sees

An Interview with Photographer Stefan Schmitz

Stefan Schmitz is a photographer living in Northern France and specializing in sensual and nude portraits. I stumbled upon his work during one of my searches for photographers using Free Software on Flickr, and as someone who loves shooting portraits his work was an instant draw for me.

He’s a member of the forums here (@beachbum) and was gracious enough recently to spare some time chatting with me. Here is our conversation (edited for clarity)…

Are you shooting professionally?

Nope, I’m not a professional photographer, and I think I’m quite happy about that. I do happen to photograph my surroundings for ±40 years now, and I have a basic idea about camera-handling and light. Being a pro is about paying invoices by shooting photos, and I fear that the pressure at the end of some months or quarters can easily take the fun out of photography. I’m an engineer and photography is my second love behind wife and kids.

Every now and then some of my pictures are requested and published by some sort of magazine, press or web-service, and I appreciate the attention and exposure, but there is no (or very little) money in the kind of photography I specialize in, so … everything’s OK the way it is.

What would you say are your biggest influences?

Starting with photographers: Andreas Feininger, Peter Lindbergh and Alfred Stieglitz. Check out the portrait of Georgia O’Keeffe by Alfred Stieglitz: it’s 100 years old and it’s all there. Pose, light, intensity, personality - nobody has invented anything [like it] afterwards. We all just try to get close. I feel the same when I look at images taken by Peter Lindbergh, but my eternal #1 is Andreas Feininger.

I got the photo-virus from my father and I learned nearly everything from daddy’s well-worn copy of The Complete Photographer ^[amzn] (Feininger) from 1965. Every single photo in that book is a masterpiece, even the strictly “instructional” ones. You measure every photo-book in the world against this one and they all finish second. Get your copy!

How would you describe your own style overall?

I shoot portraits of women and most of the time they don’t wear clothes. The portrait-part is very important for me: the model must connect with the viewer and ideally the communication goes beyond skin-deep. I want to see (and show) more than just the surface, and when that happens, I just press the shutter-button and try to get out of the way of the model’s performance.

What motivates you when deciding what/how/who to shoot?

I like women, so I take photos of women. If I were interested in beetles, I’d buy a macro lens and shoot beetles. All kidding aside, I think it’s a natural thing to do. I am married to a beautiful woman, an ex-model, and when she got fed-up with my eternal “can we do one more shoot” requests, we discussed things and she allowed me to go ahead and shoot models. Her support is very important to me, but her taste is very different from mine. I really never asked myself “why” I shoot sensual portraits and nudes. It just feels like “I want to do that” and I feel comfy with it. Does there have to be a reason?

The location is very important for me. Nothing is more boring than blinding a person with a flashlight in front of a gray wallpaper. A room, a window-sill, a landmark - there’s a lot of inspiration out there, and I often think “this is where I want to shoot”. Sometimes my wife tells me of some place she has been to or seen, and I check that out.

If you had to pick your own favorite 3 images of your work, which ones would you choose and why?

Jennifer is a very professional and inspiring model. We’ve worked together quite a number of times and while you may think that this shot was inspired by The Who’s “Pinball Wizard”, I’d answer “right band, wrong song”. It’s The Who, alright, but the song’s “A quick one while he’s away”. I chose this photo because it’s all about Jennifer’s pose and facial expression. It’s sensual, even sexy, but looking at Jennifer’s face you forget about the naked skin and all. There’s beauty, there’s depth … that’s what I’m after.

This shot of Alice is an example for the importance of natural light. There are photographers out there who can arrange light in a similar way, but I doubt that Alice would express this natural serenity in a studio setup with cables and stands and electric-transformers humming. She’s at ease, the light is perfect - I just try to be invisible because I don’t want to ruin the moment.

Try to escape Khiara’s eyes. Go, do it. It’s all there, the pose, the room, the ribbon-chair and the little icon, but those eyes make the picture. I did NOT whiten the eyeballs nor did I dodge the iris, and of course it’s all natural/available light.

If you had to pick 3 favorite images from someone else, which ones would you choose and why?

I already named Stieglitz’ Georgia O’Keeffe as an inspiration further up - next to that there’s Helmut Newton’s Big Nude III, Henrietta and Kim Basinger’s striptease in 9 ¹⁄₂ weeks (white silk nighty and all). Each one a masterpiece, each one very influential for me. Imagine the truth and depth of Georgia with the force and pride of Henrietta and the erotic playfulness of Kim Basinger. That photo would rule the world.

Is there something outside of your comfort zone you wish you could try/shoot more of?

I would like to work more with women above the age of 35, but it’s hard to find them. In general they stop modeling nude when the kids arrive.

Shooting more often outdoors would be cool, too, but that’s not easy here in northern France - there is no guarantee for good weather, and it’s frustrating when you organize a shoot two weeks in advance just to call it off in the very last minute due to bad weather.

Last but not least there’s a special competition among photographers; it’s totally unofficial and called “the white shirt contest”. Shoot a woman in a white shirt and make everybody “feel” the texture of that shirt. I give it a try on every shoot and very few pictures come out the way I wish. Go for it - it’s way harder than I thought!

How do you find your models usually?

There are websites where models and photographers can present their work and get in contact. The biggest-one worldwide is modelmayhem.com, and I highly recommend to become a member. Another good place is tumblr.com, but you have to go through a lot of dirt before you find some true gems. I have made contact via both sites and I recommend them.

You will need some pictures in your portfolio in order to show that you are - in fact - a photographer with a basic idea of portrait-work. If you shoot portraits (I mean really portraits, not some snapshots of granny and the kids under the Christmas-tree), you probably have enough photos on your disk to state the point. But if you don’t and you want to start (nude) portraits, spend some money on a workshop. I did that twice and it really helped me in several ways: communication with the model, how to start a session, do’s and don’ts - and at the end of the day you will drive home with a handful of pictures for your portfolio.

Speaking of gear, what are you shooting with currently (or what is your favorite setup)?

Gear is overrated. I am with Nikon since 1979 and today I own and use two bodies: a 1975 Nikon F2 photomic (bought used in 82), loaded with Kodak Tri-X and a Nikon D610 DSLR. 90% of my pictures are shot with a 50mm standard lens. Next on the list is the 35mm - you will need that in small rooms when the 50mm is already a bit too long and you want to keep some distance. I happen to own a 85mm, but the locations I book and shoot rarely offer enough space to make use of that lens.

There are these cheap, circular 1m silver reflectors on amazon. They cost about 15 €/$ and you get a crappy stand for the same price. That stuff is pure gold - I use the reflector a lot and I highly recommend to learn how to work with it. It’s my little secret weapon when I shoot against the light (see Alice here above).

A camera with a reasonably fast standard lens, a second battery and a silver reflector is all I need. The rest is luxury for me, but I am pretty much a one-trick-pony. Other photographers will benefit more from a bigger kit.

Most of your images appear to be making great use of natural light. Do you use other lighting gear (speedlights, monoblocks, modifiers, etc)?

Right - available light is where it’s at. I very rarely shoot with a flash kit today because it distracts me from the work with the model. I’m a loner on the set, no assistants or friends who come and help, so everything must be totally simple and foolproof.

Saying that, I own an alarming number of speedlights, umbrellas, triggers and softboxes, but I don’t need that gear very often. I try to visit the locations before I shoot. I check the directions and plan for a realistic timeframe, so today I will neither find myself in a totally dark dungeon nor in a sun-filled room with contrasts à gogo. Windows to the west - shoot in the morning, windows facing south-east: shooting in the (late) afternoon.

Here’s a shot of Karolina Lewschenko. We took this photo in a hotel room by the end of October and the available (window) light got too weak, so I used an Aurora Firefly 65 cm softbox with a Metz speedlight and set-up some classic Rembrandt-Light. I packed that gear because I knew that our timeframe wasn’t guaranteed to work out perfectly. “Better be safe than sorry”.

Do you pre-visualize and plan your shoots ahead of time usually, or is there a more organic interaction with the model and the space you’re shooting in?

Yes, I do. When I visit a place, a possible location, I have some Ideas of where to shoot, what furniture to push around and what pose to try. I can pretty much see the final picture (or my idea of it) before I book the model. Having said that, you know that no battle-plan has ever survived the first shot fired…

When the model arrives, we take some time to walk around the locations and discuss possible sets. We will then start to shoot fully clothed in order to get used to another and see how the light will be on the final shots. It’s very important for me to get feedback from the model. She might say that a pose is difficult for her or hurts after a few seconds, that she’s not comfy with something or that she would like to try a totally different thing here. I always pay a lot of attention to those ideas and - out of experience - those shots based on the model’s ideas are in general among the best of the day.

I mean we’re not here because I shoot bugs or furniture, you don’t give me the opportunity to express myself here because you are a fan of crickets; all the attention is linked to the beautiful women on my photos and how they connect with the beholder. I am just the one who captures the moments, it’s the models who fill those moments with intensity and beauty. It would be very stupid of me not to cooperate with a model who knows how to present herself and who comes up with her own ideas.

Always listen to the model, always communicate, never go quiet.

The discussion with the model also includes what degree of nudity we consider. So the second round of photos starts with the “open shirt” or topless shots before the model undresses completely. If we take photos in lingerie, we do that last (after the nudes) because lingerie often leaves traces on the skin and we don’t want that to show.

It is important to know what to do and in what order. You don’t want to have a nude model standing in front of you, asking “what’s next?” and you answer “I dunno - maybe (!) try this or that again”. If you lose your directions for a moment, just say so or say “please get your bathrobe and let’s have a look at the last pictures together”. If you are “not sure”, the model might be “not comfy”, and that’s something we want to avoid.

Would you describe your workflow a bit? Which projects do you use regularly?

A typical session is 90 to 120 minutes and I will end-up with about 500 exposures on the SD-card and maybe a roll of exposed Kodak Tri-X. The film goes to a lab and I will get the negatives and scans back within 15 to 30 days.

There’s two SD-cards, one with RAW files that I import with gThumb to /photos/year/month/day. The other card holds fine-quality JPG and those go to /pictures/year/name_of_model. My camera is already set to monochrome, I get every picture I shoot in b/w on the camera-screen and the JPG-files are also monochrome.

Next step is a pre-selection in Geeqie. That’s one great picture viewer and I delete all the missed shots (bad framing, out of focus etc.) and note/mark all the promising/good shots here. This is normally the end of day one.

Switching from RAWstudio to darktable has been a giant step for me. dt is just a great program and I still learn about new functions and modules every day. The file comes in, is converted to monochrome and afterwards color saturation and lights (red and yellow) are manipulated . This way I can treat the skin (brighter or darker) without influencing the general brightness of the picture. Highlights and lowlights may be pushed a bit to the left and I add the signature and a frame 0,5% wide, lens correction is set automatically. That’s the whole deal. On very rare occasions I add some vignette or drop the brightness gradually from top to bottom, but again: it doesn’t happen all that often. I never cut, crop or re-frame a shot. WYSIWYG. Cropping something out, turning the picture in order to get perfectly vertical lines or the likes - it all feels like cheating. I have no client to please, no deadline to meet, I can take a second longer and frame my photo when I look through the viewfinder.

The photos will then be treated in the GIMP. Some dodge and burn (especially when there are problematic, very high or low contrasts), maybe stamp an electric plug away and in the end I re-size them down to 2560 on the long side (big enough for A3 prints) and (sometimes) apply the sharpening tool with value 20 or 25. Done. I can’t save a crappy shot in post-prod and I won’t try. Out of the 500 or so frames, 10 to 15 will be processed like that and it feels like nothing has changed over the last 40 years. The golden rule was “one good shot per roll of film” and I happen to be there, too. Spot-on!

I load those 15 pictures up on my Flickr account and about once or twice a week I place a shot in the many Flickr groups. Also once a week (or every ten days) I post a photo on my Tumblr account. Today I have about 5k followers and my photos are seen between 500’000 and one million times a month, depending on the time of year and weather. There’s less traffic on warm summer days and more during cold and rainy winter-nights.

It takes me some time before I add a shot to my own website. In comparison I show few photos there, every one for a reason and I point point people to that address, so I hope I only show the best.

Is your choice to use Free Software for pragmatic reasons, or more idealistic?

I owned an Apple II in 1983 and a digital MicroVax in 1990 or so. My way to FOSS started out pragmatic and it became a conviction later on. In the late 90’s and early 2000’s I had my own small business and worked with MS Office on a Win NT machine. Photos were processed with a Nikon film-scanner through the proprietary software into an illegal copy of Adobe PS4. It was OK, stable and I didn’t fear anything, but I wasn’t really happy neither. One day I swung over to Star-Office/OpenOffice.org for financial reasons and I also got rid of that unlicensed PS and installed the GIMP (I don’t know what version, but I upgraded some time later to 1.2, that’s for sure). I had internet access and an email address since 1994, but in the late 90’s big programs still came on CDs attached to computer-magazines. Downloading the GIMP was out of question.

Gaming was never my thing and when I installed Win XP, all hell broke lose - keeping a computer safe, virus-free and running wasn’t easy before the first service pack, but MS reacted way too slow in my opinion - I tried debian (10 CD kit) on my notebook, got it running, found the GIMP and OOo - and that was it. It took a bit of trial and error and I had to buy a number of W-Lan sticks because very few were supported and so on, but in the end I got the machines running.

Later on I got hold of an Ubuntu 7.10 CD, tried that and never looked back. The few changes on my system were from Gnome to XFCE desktop and from Thunderbird to a browser-based mail-client. Xubuntu is a no-brainer, it runs stable and fast. I contribute every December 100.- € to FOSS. That’s in general 50 and 40 to two projects and a tenner to Wikipedia. I’d spend an extra tenner to any project that helps to convert old star-office files (.sdw and so on) to today’s standards (odt…), but nobody seems interested.

What is one piece of advice you would offer to another photographer?

Don’t take any advise from me, i’m still learning myself. Or wait: be kind and a gentleman with the models. They all - each and everyone of them - have had bad experiences with photographers who forgot that the models are nude for the camera, not for the man behind it. They all have been in a room with a photographer who breathes a bit too hard and doesn’t get his gear working … don’t be that arsewipe!

Arrange for a place where the model can undress in privacy - she didn’t come for a strip-show and you shouldn’t try to make it one. Have some bottles of water at hand and talk about your plans, poses and sets with the model. Few people can read minds, so communication works best when you say what you have in mind and the model says how she thinks this can be realized. The more you talk, the better you communicate, the better the pictures. No good photo has ever been shot during a quiet session, believe me.

In general the model will check your portfolio/website and expect to do more or less the same kind of work with you. If you want to do something different, say so when booking the model. If your website shows a lot of nude portraits, models will expect to do that kind of photos. They may be a bit upset if you ask them out of nowhere to wear a latex suit because it’s fetish-Friday in your world. The more open and honest you are from the beginning, the better the shooting will go down.

Don’t overdo the gear-thingy. 90% of my photos are taken with the 50mm standard lens. Period. Sometimes I have to switch to 35mm because the room is a bit to small and the distance too close for the one four-fifty, so everything I bring to an indoor-shooting is the camera, a 50, a 35, an el-cheap-o 100cm reflector from amazon (+/- 15 €/$) and an even cheaper stand for the reflector. Gear is not important, communication is.

Want to spend 300 €/$ on new gear? Spend it on a workshop. Learn how to communicate, get inspiration and fill your portfolio with a first set of pictures, so the next model you email can see that you already have some experience in the field of (nude) portraits. That’s more important than a new flashlight in your bag.

Thank You Stefan!

I want to thank Stefan again for taking the time and being patient enough to chat with me!

Stefan is currently living in Northern France. Before that he lived and worked in Miami, FL, and Northern Germany where he is from, went to school, and met his wife. His main website is at https://whatstefansees.com/, and he can be found on Flickr, Facebook, Twitter, Instagram, and Tumblr.

Unless otherwise noted, all of the images are copyright Stefan Schmitz (all rights reserved) and are used with permission.

Profiling a camera with darktable-chart

Figure out the development process of your camera

[Article updated on: 2019-06-18]

What is a camera profile?

A camera profile is often a combination of a color lookup table (LUT) and a tone curve which is applied to a RAW file to get a developed image. It translates the colors that a camera captures into the colors they should look like. If you shoot in RAW and JPEG at the same time, the JPEG file is already a developed picture. Your camera can do color corrections to the data it gets from the sensor when developing a picture. In other words, if a certain camera tends to turn blue into turquoise, the manufacturers internal profile will correct for the color shift and convert those turquoise values back to their proper hue.

The camera manufacturer creates a tone curve for the camera and understands what color drifts the camera tends to capture and can correct it. Also RAW files normally look very dull and the profile will allow it to look more pleasing with just one click. We can mimic what the camera does using a tone curve and a color LUT. We want to do this as the base curves provided by darktable are generalized for a manufacturers sensor behavior, but individually profiling your camera can provide better color results.

Why do we want a color profile?

The camera captures light as linear RGB values. RAW development software needs to transform those into CIE XYZ tristimulus values for mathematical calculations. The color transformation is often done under the assumption that the conversion from camera RGB to CIE XYZ is a linear 3x3 mapping. Unfortunately it is not because the process is spectral and the camera sensor sensitivity also absorbs spectral light. In darktable the conversion is done the following way: The camera RGB values are transformed using the color matrix (either coming from the Adobe DNG Converter or dcraw) to arrive at approximately profiled XYZ values. darktable provides color lookup table in Lab color space to fix inaccuracies or implement styles which are semi-camera independent. A very cool feature is that a user can edit the color LUT. This color LUT can be created by darktable-chart as this article will show so that you don’t have to create it yourself.

What we want to have is the same knowledge about colors in our raw development software as the manufacturer put into the camera. Therefore we have two ways to achieve this. Either we fit to a JPEG generated by the camera, which can also apply creative styles (such as film emulations, filters), or we profile against real color reproduction. For real color a color target ships with a file providing the color values for each patch it has.

In summary, we can create a profile that emulates the manufactures color processing inside the body, or we can create a profile that renders real color as accurately as possible.

The process for both is nearly identical, and we will note when it diverges in the instructions.

Creating pictures for color profiling

To create the required pictures for camera profiling we need a color chart (aka Color Checker) or an IT8 chart as our target. The difference between a color chart and IT8 chart is the number of patches and often the price. As the IT8 chart has more patches the result will be much better. Optimal would be if the color target comes with a grey card for creating a custom White Balance. I can recommend the X-Rite ColorChecker Passport Photo. It is small, lightweight, all plastic, a good quality tool and also has a gray card. An alternative is the Spyder Checkr. If you want a better profiling result, you can buy a good IT8 chart from Coloraid (you want C1) or invest for example in the ColorChecker Digital SG. (Please share you experience if you buy a Coloraid C1!). I recommend getting a gray card as this makes profiling easier.

Note: ArgllCMS offers CIE and CHT files for different color charts, if you already have one or are going to buy one, check if ArgyllCMS offers support for it first! You can always add support to your color chart to ArgylCMS, but the process is much more complex. This will be very important later! You can find these files (generally) in:

/usr/share/color/argyll/ref/

The path might differ depending on the distribution you’re using. Your package management tool should provide a way to list all files of a package so it should be easy to find.

find /usr/share -name "*.cht"

is a possible alternative to track down where the files are located.

We are creating a color profile for direct sunlight conditions (D50) which can be used as a general purpose profile. For this we need some special conditions.

The Color Checker needs to be photographed in direct sunlight at 5000K (K = Kelvin), which helps to reduce any metamerism of colors on the target and ensures a good match to the data file that tells the profiling software what the colors on the target should look like. However a major concern is glare, but we can reduce it with some tricks.

One of the things we can do to reduce glare, is to build a simple shooting box. For this we need a cardboard box and at least three black T-Shirts. The box should be open on the top and on the front like in the following picture (Figure 1).

Normally you just need to cut one side open. However it is better if you use one big cardboard and build the box yourself. This way you can make the box so it widens up in the front, see Figure 1. Then coat the inside of the box with black T-Shirts like this:

To further reduce glare we just need the right location to shoot the picture. We want to shoot the target when the sun provides a temperature of 5000K (D50). We get that in the morning hours when the sun is at about 45° in the sky. It varies on where on earth you are located and on the season of the year.

I took my shots in central Europe in mid October at 09:45.

To measure 5000K I used a gray card for white balancing. When I shoot the gray card, my camera displayed which temperature the profile has.

Try to shoot on a day with minimal clouds so the sun isn’t changing intensity while you shoot. The higher the temperature the more water is in the atmosphere, which means the quality of the images for profiling might be reduced. Temperatures below 20°C are better than above.

In some countries it may not be possible to accurately produce these images with sunlight. This could be due to air pollution (or lack of), temperature, humidity, latitude, and atmospheric conditions. For example, in Australia, one might be unable to use direct sunlight to create this profile, and would have to use a set of color balanced bulbs with the same box setup to create this.

Shooting outdoor

If you want to shoot outdoor, look for an empty tared parking lot or a lonely road. The parking lot should be pretty big, like from a mall, without any cars or trees! You should be far away from walls, trees or anything which could possibly reflect. Put the box on the ground or a small chair and shoot with the sun above your right or left shoulder behind you. You can use a black fabric (bed sheets) if the ground reflects.

Shooting indoor with artificial light

Avoid all windows and stained glass. Create the box as mentioned, and arrange it in a V shape with your tripod. At the top left of the V is the camera, at the bottom is the color target, and at the top right is the light source. The right source should be bright and even across the room and your setup. Position yourself underneath it to avoid all shadows.

How to shoot the target?

Outdoor preparations

1. Start white balancing your camera outside your house, office etc. with a gray card every hour or 30 mintues in the morning and write down the time and temperature. This way you will find out when the sun provides the right temperatue (5000K) to take pictures for your target.

Taking the pictures

Preparations at home

If you’re shooting outdoor, do the following preparations at home. You will not have much time for taking the pictures of your target. You only have a Window of about 10 minutes. An assitent in the field can be useful.

1. You should use a prime lens for taking the pictures. If possible a 50 mm or 85 mm lens (or anything in between, numbers are for full frame). The less glass the light has to travel through the better it is for profiling. Thus those two lenses are a good choice in the number of glass elements they have and their field of view and also vignetting! With a tele lens we would be too far away and with a wide angle lens we would need to be too near to have just the black box in the picture.

2. Set your metering mode to matrix metering (evaluative metering or multi metering - this is often a symbol with 4 boxes and a circle in the center) and use an aperture of f/8.0 (+/- 1/3 EV). [If you have a spot metering mode which isn’t fixed on the center, then you can point it to the neutral gray patch of the color checker, that’s the one we want to have exposed correctly.]

3. Make sure that Dynamic Range Optimization (DRO) and Auto HDR (High Dynamic Range) or anything like that are turned off!

4. Set the camera to capture “RAW & JPEG” and disable lens corrections (vignetting corrections) for JPEG files if possible. This is important for JPEG and real color fitting. You can leave corrections for color failures turned on.

5. Set your camera to color profile to AdobeRGB.

6. Set the ISO to the lowest possible value. Some cameras have an extended ISO range, don’t use any of those values. For example my camera offers ISO 50, ISO 64 and ISO 80. Those are extended ISO values. The lowest ISO not in the extended range for my camera is ISO 100. Check your camera manual!

7. Wear dark cloths, the best is a black hoody with long sleeves :-)

In the field

Be there in advance so you have time to prepare everything.

1. Set up your shooting box and mount your camera on a tripod. The best is to have the camera looking down on the color chart like in the following picture:

2. Make sure the color chart is parallel to plane of the camera sensors so all patches of the chart are in focus. The color chart should be in the middle of the image using about 1/3 of the screen so that vignetting is not an issue.

3. Shoot the target, zoom to 100% and check for glare and reposition if necessary! In Figure 3b you can see a patch with extreme glare. In Figure 3c you can see a patch with a bit of glare. You should try to get no glare at all. Make sure the sun is shining at an angle on the Color Checker. Change the angle of the target in to box till you get no glare!

3. If your camera has a custom white balance feature and you have a gray card, create a custom white balance profiles till you get 5000K (D50) and use it (see figure 3). Put the gray card in your black box in the sunlight or artificial light at the same position as the Color Checker. If you don’t have a gray card, you have to use Auto White Balance (AWB) and find other ways how to measure when you get 5000K from the sun.

   Once you get 5000K from the the sun, you have about 10 minutes to take the pictures of your target!

Now you want to begin taking images. Normally we want to have a camera profile just for the lowest ISO value.

Note: I created profiles for ISO 100 to ISO 640, because my camera has a gain switch at ISO 640. I learned about that by inspecting the charts which have been measured by DPReview.

You need to take 5 pictures of your target. This is so that if an image is over or under exposed, you have an image with a stop above or below that is then exposed correctly. One photo for -0.3 EV, 0 EV, 0.3 EV, 0.7 EV and 1.0 EV. Some cameras (Fuji) ISO 100 is an Extended value, so use ISO 200. Normally Extended ISO values are captured with the lowest physical ISO and overexposed and then exposure is reduced with image processing. Use the lowest ISO profile for them.

Hint: Some cameras have a “Continues Bracketing” feature. You can set this to 0.3EV and 5 Images. Then the camera will automatically capture 5 images in 0.3 EV stops (-0.3 EV, 0.0 EV, 0.3 EV, 0.7 EV, 1.0 EV) for you.

Once you have done all the required shots, it is time to download the RAW and JPEG files to your computer.

Verifying correct images in darktable

For verifying the images we need to know the L-value from the Lab color space of the neutral gray field in the gray ramp of our color target. For the ColorChecker Passport we can look it up in the color information (CIE) file (ColorCheckerPassport.cie) shipping with ArgyllCMS, which should be located at:

/usr/share/color/argyll/ref/ColorCheckerPassport.cie

The ColorChecker Passport has actually two gray ramps. The neutral gray field is the field on the bottom right of the color target ramp and is called D1 (see Figure 4). For the ColorChecker SG it is the patch E5 and for Wolf Faust’s IT8 target the one on the left of the gray ramp (GS0). It should be described in the specification of your target.

If we check the CIE file, we will find out that the neutral gray field D1 has an L-value of: L=96.260066. Lets round it to L=96. For other color targets you can find the L-value in the description or specification of your target, often it is L=92 (e.g. Wolf Faust’s IT8 GS0). Better check the CIE or CGATS file!

You then open the RAW file in darktable and disable the base curve and all other modules which might be applied automatically! You can leave the Orientation module turned on. Select the standard input matrix in the input color profile module and disable gamut clipping. Make sure “camera white balance” in the white balance module is selected. If lens corrections are automatically applied to your JPEG files, you need to enable lens corrections for your RAW files too! Only apply what has been applied to the JPEG file too.

For my configuration I was left with the following modules enabled:

Output Color Profile
Input Color Profile
Lens Correction (Optional)
Crop & Rotate (Optional)
Demosaic
White Balance
Raw Black/White Point

Apply the changes to all RAW files you have created!

You could consider making a “profiling” style and applying it en-masse.

You can also crop the image but you need to apply exactly the same crop to the RAW and JPEG file! (This is why you use a tripod!)

Now we need to use the global color picker module in darkroom to find out the value of the natural white field on the color target.

• Open the first RAW file in darkroom and expand the global color picker module on the left.
• Select area, mean and Lab in the color picker and use the eye-dropper to select the natural gray field of your target. On the Color Checker it’s on the bottom right. Here is an example:

• If the value displayed in the color picker module matches the L-value of the field or is close (+0/-2. This means L=94 to L=96 is acceptable), give the RAW file and the corresponding JPEG file 5 stars. In the picture above it is the first value of: (96.491, -0.431, 3.020). This means L=96.491, which is what you’re looking for on this color target. You might be looking for e.g. L=92 if you are using a different Color Checker. See above how to find out the L-value for your target.

• For real color profiling this is very important to get right. Additionally you want to check the JPEG is registering a L value between 96 and 98 (0/+2 tolerance). You do not want overexposure here (L=100 is white)! If your images are over exposed, your profile will actually darken the images (this is not what you want).

• For profile extraction, this is less important as darktable-chart will extract the differences between the raw and the JPEG, and will assume the camera’s exposure level was correct. This means if your camera “thinks” a good exposure is L=98 for the JPEG, and the RAW reads as L=85, then your profile needs to create the difference here so you get the same effect.

Exporting images for darktable-chart

For exporting we need to select Lab as output color profile. This color space is not visible in the combo box by default. You can enable it by starting darktable with the following command line argument:

darktable --conf allow_lab_output=true

Or you always enable it by setting allow_lab_output to TRUE in darktablerc. Make sure that you have closed darktable before making this change, then reopen it ( darktable writes to this file and may erase your change if you edit while darktable is running).

~/.config/darktable/darktablerc
allow_lab_output=TRUE

As the output format select “PFM (float)” and for the export path you can use:

$(FILE_FOLDER)/PFM/$(MODEL)_ISO$(EXIF_ISO)_$(FILE_EXTENSION)

Remember to select the Lab output color profile here as well.

You need to export all the RAW and JPEG files, not just the RAWs.

Select all 5 star RAW and JPEG files and export them.

Profiling with darktable-chart

Before we can start you need the chart file for your color target. The chart file contains the layout of the color checker. For example it tells the profiling software where the gray ramp is located or which field contains which color. For the “X-Rite Colorchecker Passport Photo” there is a (ColorCheckerPassport.cht) file provided by ArgyllCMS. You can find it here:

/usr/share/color/argyll/ref/ColorCheckerPassport.cht

Now it is time to start darktable-chart. The initial screen will look like this:

Source Image

In the source image tab, select your PFM exported RAW file as image and for chart your Color Checker chart file. Then fit the displayed grid on your image.

Make sure that the inner rectangular of the grid is completely inside of the color field, see Figure 8. If it is too big, you can use the size slider in the top right corner to adjust it. Better too small than too large.

Reference values

This is the only step where the process diverges for real color vs camera profile creation.

If you are creating a color profile to match the manufacturers color processing in body, you will want to select color chart image and as the reference image select the PFM exported JPEG file which corresponds to the RAW file in the source image tab. Once opened you need to resize the grid again to match the Color Checker in your image. Adjust the size with the slider if necessary.

If you are creating a color profile for real color, select the mode as cie/it8 file and load the corresponding CIE file for your color target. If you have issues with this, run darktable-chart from the CLI and check the output. I found that my chart would not open with:

error with the IT8 file, can't find the SAMPLE_ID column

It’s worth checking the ‘Lab (reference)’ values at the bottom of the display to ensure they match what you expect and were correctly loaded. I saw some cool (but incorrect) results when they did not load!

Process

In this tab you’re asked to select the patches with the gray ramp. For the ‘X-Rite Color Checker Passport’ these are the ‘NEU1 .. NEU8’ fields. Newer version of darktable automatically detect the gray ramps! The input field number of final patches defines how many editable color patches the resulting style will use within the color look up table module. More patches give a better result but slows down the process. I think 28 is a good compromise but you might want to user the maxium of 49.

Once you have done this click on ‘process’ to start the calculation. The quality of the result in terms of average delta E and maximum delta E are displayed below the button. These data show how close the resulting style applied to the source image will be able to match the reference values – the lower the better.

You must click process each time you change source images or reference chart to generate the new profiles. Sometimes process is “greyed out”, so simply toggling the grey ramp setting will reactivate it.

After running ‘process’, click on ‘export’ to save the darktable style.

In the export window you should already get a good name for the style. Add a leading zero for ISO values smaller than 1000 get correct sorting in the styles module, for example: ILCE-7M3_ISO0100_JPG.dtstyle. The JPG in the name should indicate that we fitted against a JPG file. If you fitted against a CIE file, remove the CIE filename from the style name. If you applied a creative style (for example, a film emulation or filter in the camera). to the JPG, probably add it at the end of the file name and style name.

Importing your dtstyle in darktable

To use your just created style, you need to import it in the style module in the lighttable. In the lighttable open the module on the right and click on ‘import’. Select the dtstyle file you created to add it. Once imported you can select a raw file and then double click on the style in the ‘style module’ to apply it.

Open the image in darkroom and you will notice that the base curve has been disabled and a few modules been enabled. The additional modules activated are normally: input color profile, color lookup table and tone curve.

Verifying your profile

To verify the style you created you can either apply it to one of the RAW files you created for profiling. Then use the global color picker to compare the color in the RAW with the style applied to the one in the JPEG file.

I also shoot a few normal pictures with nice colors like flowers in RAW and JPEG and then compare the result. Sometimes some colors can be off which can indicate that your pictures for profiling are not the best. This can be because there were some kind of clouds, glare or the wrong daytime. Redo the shots till you get the result you’re satisfied with.

Sadly this is a trial and error process, so you will have to create some number of profiles before you find the results you want. It’s a good idea to read this article again to see if you missed any important steps.

How does the result look like?

In the following screenshot (Figure 11) you can see the calculated tone curve by darktable chart and the Sony base curve of darktable. The tone curve is based on the color LUT. It will look flat if you apply it without the LUT.

Here is a comparison between the base curve for Sony on the left and the dtstyle (color LUT + tone curve) created with darktable-chart:

Other ideas

This process will work for extracting in-body black and white profiles, as well as creative color profiles. I see a significant improvment in black and white profiles from this process over the use of some of the black and white modules in darktable.

You may find that the lowest ISO profile may provide pretty good results for higher ISO values. This will save you a lot of time profiling, and allows you to blanket-apply your profile to all your images quickly - you only need one profile now! This is highly dependant on your camera however, so experiment with this.

These profiles should work in all light conditions, provided your white balance is correct. Given you now have a color target, you should always take one photo of it, so you can correct the whitebalance later.

Discussion

As always the ways to get better colors are open for discussion an it can be improved in collaboration.

Feedback is very welcome.

Thanks to the darktable developers for such a great piece of software! :-)

William Brown has contributed to the article, based on his profiling experience following this tutorial.

How to create camera noise profiles for darktable

An easy way to create correct profiling pictures

[Article updated on: 2019-11-26]

What is noise?

Noise in digital images is similar to film grain in analogue photography. In digital cameras, noise is either created by the amplification of digital signals or heat produced by the sensor. It appears as random, colored speckles on an otherwise smooth surface and can significantly degrade image quality.

Noise is always present, and if it gets too pronounced, it detracts from the image and needs to be mitigated. Removing noise can decrease image quality or sharpness. There are different algorithms to reduce noise, but the best option is if having profiles for a camera to understand the noise patterns a camera model produces.

Noise reduction is an image restoration process. You want to remove the digital artifacts from the image in such a way that the original image is discernible. These artifacts can be just some kind of grain (luminance noise) or colorful, disturbing dots (chroma noise). It can either add to a picture or detract from it. If the noise is disturbing, we want to remove it. The following pictures show a picture with noise and a denoised version:

To get the best noise reduction, we need to generate noise profiles for each ISO value for a camera.

Creating the pictures for noise profiling

For every ISO value your camera has, you have to take a picture. The pictures need to be exposed a particular way to gather the information correctly. The photos need to be out of focus with a widespread histogram like in the following image:

We need overexposed and underexposed areas, but mostly particularly the grey areas in between. These areas contain the information we are looking for.

Let’s go through the noise profile generation step by step. For easier creation of the required pictures, we will create a stencil which will make it easier to capture the photos.

Building a profiling testbed

Requiements

• A dark room (wait till night time)
• Monitor
• Printer
• Sheets of black thick paper (DIN A3, >= 200g/m²)
• White paper
• Scissors
• Sellotape (Tesafilm)

First you need to get some thicker black paper or cardboard. No light should shine through it! Then you need to print out a gradient on white paper. Light should shine through the white paper!

Print this black to white gradient (PDF)

I got black thick paper (DIN A3, >= 200g/m²) and used two sheets. You need to be able to cover your monitor with the black paper. Put the printed gradient in the middle and draw around it. From three sides (bottom, left, top) make the window smaller by 1 cm, see Figure 1. On the right we need to have a gap.

Next is to cut out the window and type the gradient onto the black paper like in Figure 2. It is important that there is a gap between the white and the black paper on the white side of the gradient. We need light for an overexposed area.

Once you have done that go to your monitor and make it all white. You can an all white image for that. Then tape the sheets to your monitor like in Figure 3.

Taking the pictures

It is time to get your camera. You need to shoot in RAW. It is best to turn off any noise reduction especially long exposure noise reduction. Mount the camera on a tripod and use a lens between 35 mm to 85 mm (full frame). I used a 85 mm f/1.4 lens.

Make sure the gradient fills most of the frame. Set your camera to manual focus and focus on infinity. Select the manual mode of your camera and choose the fastest aperture and ISO100. Depending on the lens you’re using you might want to close the aperture. For me f/1.4 was too blurry and I closed it till f/4.0. You don’t want to see any edges or any structure on the paper but be too blurry. You want to still see the gradient but we want nice transitions between different lightning zone black -> grey -> white like in Figure 4.

Now you need to set the shutter speed. Make the picture really dark and then make the shutter speed longer till the gap which gives us the white from the monitor is overexposed, pure white see Figure 4. The black around the white paper should be underexposed (pure black).

Now you need to take a picture for each ISO value of your camera. When you increase the ISO value you need to decrease the shutter speed!

Creating the noise profiles

STEP 1

Run

/usr/lib/darktable/tools/darktable-gen-noiseprofile --help

If this gives you the help of the tool, continue with STEP 2 otherwise go to STEP 1a. Packages for openSUSE, Fedora, Ubuntu and Debian packaging the noise tools can be found here.

STEP 1a

Your darktable installation doesn’t offer the noise tools so you need to compile it yourself. Before you start make sure that you have the following dependencies installed on your system:

• git
• gcc
• make
• gnuplot
• convert (ImageMagick)
• darktable-cli

Get the darktable source code using git:

git clone https://github.com/darktable-org/darktable.git

Now change to the source and build the tools for creating noise profiles using:

mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/opt/darktable -DBUILD_NOISE_TOOLS=ON ..
cd tools/noise
make
sudo make install

STEP 2

Download the pictures from your camera and change to the directory on the command line:

cd /path/to/noise_pictures

and run the following command:

/usr/lib/darktable/tools/darktable-gen-noiseprofile -d $(pwd)

or if you had to download and build the source, run:

/opt/darktable_source/lib/tools/darktable-gen-noiseprofile -d $(pwd)

This will automatically do everything for you. Note that this can take quite some time to finish. I think it took 15 to 20 minutes on my machine. If a picture is not exposed correctly, the tool will tell you the image name and you have to recapture the picture with that ISO. Remove the non-working picture.

The tool will tell you, once completed, how to test and verify the noise profiles you created.

Once the tool finished, you end up with a tarball you can send to darktable for inclusion. You can open a bug here

The interesting files are the presets.json file (darktable input) and, for the developers, the noise_result.pdf file. You can find an example PDF here. It is a collection of diagrams showing the histogram for each picture and the results of the calculations.

A detailed explanation of the diagrams and the math behind it can be found in the original noise profile tutorial by Johannes Hanika.

Feedback is very much welcome in the comments below!

G'MIC 2.2

New features and filters!

The IMAGE team of the GREYC laboratory (UMR CNRS 6072, Caen, France) is pleased to announce the release of a new 2.2 version of G’MIC, its open-source, generic, and extensible framework for image processing. As we already did in the past, we take this opportunity to look at the latest notable features added since the previous major release (2.0, last June).

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• The G’MIC project
• Twitter feed
• The G’MIC Online Web Service

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Note 1: click on a picture to view a larger version. Note 2: This is a translation of an original article, in French, published on Linuxfr.

1. Context and recent evolutions

G’MIC is a free and open-source software developed since August 2008 (distributed under the CeCILL license), by folks in the IMAGE team at the GREYC, a French public research laboratory located in Caen and supervised by three institutions: the CNRS, the University of Caen, and the ENSICAEN engineering school. This team is made up of researchers and lecturers specialized in the fields of algorithms and mathematics for image processing. As one of the main developer of G’MIC, I wanted to sum up the work we’ve made on this software during these last months.

G’MIC is multi-platform (GNU/Linux, MacOS, Windows …) and provides many ways of manipulating generic image data, i.e. still images or image sequences acquired as hyperspectral 2D or 3D floating-point arrays (including usual color images). More than 950 different image processing functions are already available in the G’MIC framework, this number being expandable through the use of the G’MIC scripting capabilities.

Since the last major version release there have been two important events in the project life:

1.1. Port of the G’MIC-Qt plugin to Krita

When we released version 2.0 of G’MIC a few months ago, we were happy to announce a complete rewrite (in Qt) of the plugin code for GIMP. An extra step has been taken, since this plugin has been extended to fit into the open-source digital painting software Krita. This has been made possible thanks to the development work of Boudewijn Rempt (maintainer of Krita) and Sébastien Fourey (developer of the plugin). The G’MIC-Qt plugin is now available for Krita versions 3.3+ and, although it does not yet implement all the I/O functionality of its GIMP counterpart, the feedback we’ve had so far is rather positive. This new port replaces the old G’MIC plugin for Krita which has not been maintained for some time. The good news for Krita users (and developers) is that they now have an up-to-date plugin whose code is common with the one running in GIMP and for which we will be able to ensure the maintenance and further developments. Note this port required the writing of a source file host_krita.cpp (in C++) implementing the communication between the host software and the plugin, and it is reasonable to think that a similar effort would allow other programs to get their own version of the G’MIC plugin (and the 500 image filters that come with it!).

1.2. CeCILL-C, a more permissive license

Another major event concerns the new license of use : The CeCILL-C license (that is in the spirit of the LGPL) is now available for some components of the G’MIC framework. This license is more permissive than the previously proposed CeCILL license (which is GPL-compatible) and is more suitable for the distribution of software libraries. This license extension (now double licensing) applies precisely to the core files of G’MIC, i.e. its C++ library libgmic. Thus, the integration of the libgmic features (therefore, all G’MIC image filters) is now allowed in software that are not themselves licensed under GPL/CeCILL (including closed source products). The source code of the G’MIC-Qt plugin, meanwhile, remains distributed under the single CeCILL license (GPL-like).

2. Fruitful collaboration with David Revoy

If you’ve followed us for a while, you may have noticed that we very often refer to the work of illustrator David Revoy for his multiple contributions to G’MIC: mascot design, ideas of filters, articles or video tutorials, tests of all kinds, etc. More generally, David is a major contributor to the world of free digital art, as much with the comic Pepper & Carrot he produces (distributed under free license CC -BY), as with his suggestions and ongoing bug reports for the open-source software he uses. Therefore, it seems quite natural to devote a special section to him in this article, summarizing the different ideas, contributions and experiments he has brought to G’MIC just recently. A big thank you, David for your availability, the sharing of your ideas, and for all your work in general!

2.1. Improving the lineart colorization filter

Let’s first mention the progress made on the Black & White / Colorize lineart (smart-coloring) filter that had appeared at the time of the 2.0 G’MIC release. This filter is basically a lineart colorization assistant which was developed in collaboration with David. It tries to automatically generate a colorization layer for a given lineart, from the analysis of the contours and the geometry of that lineart. Following David‘s suggestions, we were able to add a new colorization mode, named “Autoclean“. The idea is to try to automatically “clean” a coloring layer (made roughly by the user) provided in addition to the lineart layer, using the same geometric analysis as for the previous colorization modes. The use of this new mode is illustrated below, where a given lineart (left) has been colorized approximately by the user. From the two layers line art + color layer, our “Autoclean“ algorithm generates an image (right), where the colors do not overflow the lineart contours (even for “virtual” contours that are not closed). The result is not always perfect, but nevertheless reduces the time spent in the tedious process of colorization.

Note that this filter is also equipped with a new hatch detection module, which makes it possible to avoid generating too many small areas when using the previously available random colorization mode, particularly when the input lineart contains a large number of hatches (see figure below).

2.2. Color equalizer in HSI, HSL and HSV spaces

More recently, David suggested the idea of a filter to separately vary the hue and saturation of colors having certain levels of luminosity. The underlying idea is to give the artist the ability to draw or paint digitally using only grayscale, then colorize his masterpiece afterwards by re-assigning specific colors to the different gray values of the image. The obtained result has of course a limited color range, but the overall color mood is already in place. The artist only has to retouch the colors locally rather than having to colorize the entire painting by hand. The figure below illustrates the use of this new filter Colors/Equalize HSI/HSL/HSV available in the G’MIC plugin : each category of values can be finely adjusted, resulting in preliminary colorizations of black and white paintings.

Note that the effect is equivalent to applying a color gradient to the different gray values of the image. This is something that could already be done quite easily in GIMP. But the main interest here is we can ensure that the pixel brightness remains unchanged during the color transformation, which is not an obvious property to preserve when using a gradient map. What is nice about this filter is that it can apply to color photographs as well. You can change the hue and saturation of colors with a certain brightness, with an effect that can sometimes be surprising, like with the landscape photography shown below.

2.3. Angular deformations

Another one of the David‘s ideas concerned the development of a random local deformation filter, having the ability to generate angular deformations. From an algorithmic point of view, it seemed relatively simple to achieve. Note that once the implementation has been done (in concise style: 12 lines!) and pushed into the official filter updates, David just had to press the “Update Filters“ button of his G’MIC-Qt plug-in, and the new effect Deformations/Crease was there immediately for testing. This is one of the practical side of developing new filters using the G’MIC script language!

However, I must admit I didn’t really have an idea on what this could be useful for in practice. But the good thing about cooperating with David is that HE knows exactly what he’s going to do with it! For instance, to give a crispy look to the edges of his comics, or for improving the render of his alien death ray.

3. Filters, filters, filters…

David Revoy is not the only user of G’MIC: we sometimes count up to 900 daily downloads from the main project website. So it happens, of course, that other enthusiastic users inspire us new effects, especially during those lovely discussions that take place on our forum, kindly made available by the PIXLS.US community.

3.1. Bring out the details without creating “halos”

Many photographers will tell you that it is not always easy to enhance the details in digital photographs without creating naughty artifacts that often have to be masked manually afterwards. Conventional contrast enhancement algorithms are most often based on increasing the local variance of pixel lightness, or on the equalization of their local histograms. Unfortunately, these operations are generally done by considering neighborhoods with a fixed size and geometry, where each pixel of a neighborhood is always considered with the same weight in the statistical calculations related to these algorithms. It is simpler and faster, but from a qualitative point of view it is not an excellent idea: we often get “halos” around contours that were already very contrasted in the image. This classic phenomenon is illustrated below with the application of the Unsharp mask filter (the one present by default in GIMP) on a part of a landscape image. This generates an undesirable “halo” effect at the frontier between the mountain and the sky (this is particularly visible in full resolution images).

The challenge of the detail enhancement algorithms is to be able to analyze the geometry of the local image structures in a more fine way, to take into account geometry-adaptive local weights for each pixel of a given neighborhood. To make it simple, we want to create anisotropic versions of the usual enhancement methods, orienting them by the edges detected in the images. Following this logic, we have added two new G’MIC filters recently, namely Details/Magic details and Details/Equalize local histograms, which try to better take the geometric content of the image into account for local detail enhancement (e.g. using the bilateral filter).

Thus, the application of the new G’MIC local histogram equalization on the landscape image shown before gives something slightly different : a more contrasted result both in geometric details and colors, and reduced halos.

3.2. Different types of image deformations

New filters to apply geometric deformations on images are added to G’MIC on a regular basis, and this new major version 2.2 offers therefore a bunch of new deformation filters. So let’s start with Deformations/Spherize, a filter which allows to locally distort an image to give the impression that it is projected on a 3D sphere or ellipsoid. This is the perfect filter to turn your obnoxious office colleague into a Mr. Potato Head!

On the other hand, the filter Deformations/Square to circle implements the direct and inverse transformations from a square domain (or rectangle) to a disk (as mathematically described on this page), which makes it possible to generate this type of deformations.

The effect Degradations/Streak replaces an image area masked by the user (filled with a constant color) with one or more copies of a neighboring area. It works mainly as the GIMP clone tool but prevents the user to fill the entire mask manually.

3.3. Artistic Abstractions

You might say that image deformations are nice, but sometimes you want to transform an image in a more radical way. Let’s introduce now the new effects that turn an image into a more abstract version (simplification and re-rendering). These filters have in common the analysis of the local image geometry, followed by a step of image synthesis.

For example, G’MIC filter Contours/Super-pixels locally gathers the image pixels with the same color to form a partitioned image, like a puzzle, with geometric shapes that stick to the contours. This partition is obtained using the SLIC method (Simple Linear Iterative Clustering), a classic image partitioning algorithm, which has the advantage of being relatively fast to compute.

The filter Artistic/Linify tries to redraw an input image by superimposing semi-transparent colored lines on an initially white canvas, as shown in the figure below. This effect is the re-implementation of the smart algorithm initially proposed on the site http://linify.me (initially implemented in JavaScript).

The effect Artistic/Quadtree variations first decomposes an image as a quadtree, then re-synthesize it by drawing oriented and plain ellipses on a canvas, one ellipse for each quadtree leaf. This renders a rather interesting “painting” effect. It is likely that with more complex shapes, even more attractive renderings could be synthesized. Surely an idea to keep in mind for the next filters update :)

3.4. “Are there any more?”

And now that you have processed so many beautiful pictures, why not arrange them in the form of a superb photo montage? This is precisely the role of the filter Arrays & tiles/Drawn montage, which allows to create a juxtaposition of photographs very quickly, for any kind of shapes. The idea is to provide the filter with a colored template in addition to the serie of photographs (Fig.3.10a), and then to associate each photograph with a different color of the template (Fig.3.10b). Next, the arrangement is done automatically by G’MIC, by resizing the images so that they appear best framed within the shapes defined in the given montage template (Fig.3.10c). We made a video tutorial illustrating the use of this specific filter.

But let’s go back to more essential questions: have you ever needed to draw gears? No?! It’s quite normal, that’s not something we do everyday! But just in case, the new G’MIC filter Rendering/Gear will be glad to help, with different settings to adjust gear size, colors and number of teeth. Perfectly useless, so totally indispensable!

Need a satin texture right now? No?! Too bad, the filter Patterns / Satin could have been of a great help!

And finally, to end up with the series of these “effects that are useless until we need them”, note the apparition of the new filter Degradations/JPEG artifacts which simulates the appearance of JPEG compression artifacts due to the quantization of the DCT coefficients encoding 8×8 image blocks (yes, you will get almost the same result saving your image as a JPEG file with the desired quality).

4. Other notable improvements

This review of these new available G’MIC filters should not overshadow the various improvements that have been made “under the hood” and that are equally important, even if they are less visible in practice for the user.

4.1. A better G’MIC-Qt plugin interface

A big effort of cleaning and restructuring the G’MIC-Qt plugin code has been realized, with a lot of little inconsistencies fixed in the GUI. Let’s also mention in bulk order some new interesting features that have appeared in the plugin:

• The ability to set a timeout) when trying to preview some computationnaly intensive filters.
• A better management of the input-output parameters for each filter (with persistence, better menu location, and a reset button).
• Maximizing the size of the preview area is now easier. Editing its zoom level manually is now possible, as well as chosing the language of the interface (regardless of the language used for the system), etc.

All these little things gathered together globally improves the user experience.

4.2. Improvements in the G’MIC core

Even less visible, but just as important, many improvements have appeared in the G’MIC computational core and its associated G’MIC script language interpreter. You have to know that all of the available filters are actually written in the form of scripts in the G’MIC language, and each small improvement brought to the interpreter may have a beneficial consequence for all filters at once. Without going too much into the technical details of these internal improvements, we can highlight those points:

• The notable improvement in the syntax of the language itself, which goes along with better performances for the analysis of the language syntax (therefore for the script executions), all this with a smaller memory footprint.

• The G’MIC built-in mathematical expression evaluator is also experiencing various optimizations and new features, to consider even more possibilities for performing non-trivial operations at the pixel level.

• A better support of raw video input/outputs (.yuv format) with support for4:2:2 and 4:4:4 formats, in addition to4:2:0 which was the only mode supported before.

• Finally, two new animations have been added to the G’MIC demos menu (which is displayed e.g. when invoking gmic without arguments from the command-line):

  • First, a 3D starfield animation:

  

  • Second, a playable 3D version of the Tower of Hanoi:

  

• Finally, let us mention the introduction of the command tensors3d dedicated to the 3D representation of second order tensor fields. In practice, it does not only serve to make you want to eat Smarties^®! It can be used for example to visualize certain regions of MRI volumes of diffusion tensors:

  

4.3. New design for G’MIC Online

To finish this tour, let us also mention the complete redesign of G’MIC Online during the year 2017, done by Christophe Couronne and Véronique Robert from the development departement of the GREYC laboratory. G’MIC Online is a web service allowing you to apply a subset of G’MIC filters on your images, directly inside a web browser. These web pages now have a responsive design, which makes them more enjoyable than before on mobile devices (smartphones and tablets). Shown below is a screenshot of this service running in Chrome/Android, on a 10’’ tablet.

5. Conclusion and perspectives

The overview of this new version 2.2 of G’MIC is now over. One possible conclusion could be: “There are plenty of perspectives!“.

G’MIC is a free project that can be considered as mature: the first lines of code were composed almost ten years ago, and today we have a good idea of the possibilities (and limits) of the beast. We hope to see more and more interest from FOSS users and developers, for example for integrating the G’MIC-Qt generic plugin in various software focused on image or video processing.

The possibility of using the G’MIC core under a more permissive CeCILL-C license can also be a source of interesting collaborations in the future (some companies have already approached us about this). While waiting for potential collaborations, we will do our best to continue developping G’MIC and feed it with new filters and effects, according to the suggestions of our enthusiastic users. A big thanks to them for their help and constant encouragement (the motivation to write code or articles, past 11pm, would not be the same without them!).

“Long live open-source image processing and artistic creation!”

LGM and Libre Graphics at SCaLE 16x

All the libre graphics!

There are two libre graphics related meetings coming up early next year. The annual Libre Graphics Meeting (in Spain this year), and something entirely new: a libre graphics track at SCaLE. How exciting!

Libre Graphics Meeting 2018

The Libre Graphics Meeting is going to be in Seville, Spain this year. They recently published their Call for Participation and are accepting presentation and talk proposals now. Unfortunately, I won’t be able to attend this year, but there’s a pretty good chance some friendlier folks from the community will be! We’ll update more about who will be making it out as soon as we know, and maybe we can convince someone to run another photowalk with everyone. (On a side note, if anyone from the community is going to make it and wants a hand putting anything together for a presentation just let us know - we’re here to help.)

Libre Graphics at SCaLE (California, USA)

This year we have a neat announcement - due to some prodding from Nate Willis, we have been given a day at the Southern California Linux Expo (SCaLE) to hold a Libre Graphics focused track! The expo is at the Pasadena Convention Center, March 8-11, 2018.

We first had a chance to hang out with LWN editor Nate Willis during the Libre Graphics Meeting 2016 in London, and later out at the Texas Linux Fest. GIMP was able to have both Akkana Peck and myself out to present on GIMPy stuff and host a photowalk as well.

The organizer for SCaLE, Ilan, was kind enough to give us a day (Friday, March 9^th) and a room for all the libre graphics artists, designers, programmers, and hackers.

I will be in attendance promoting GIMP stuff in the main track, Dr. Ullah (Isaac Ullah) will hopefully be presenting, and Mica will be there (@paperdigits) as well. I’m pretty certain we’ll be holding a photowalk for attendees while we’re there - and we may even setup a nice headshot booth in the expo to take free headshots for folks.

We would love to see some folks out there. If you think you might be able to make it, or even better submit a talk proposal, please come and join us! (I was thinking about getting an AirBnB to stay in, so if folks let me know they are going to make it out we can coordinate a place to all stay together.)

SCaLE Libre Graphics Track Call for Participation

The libre graphics community is thrilled to announce that a special, one-day track at SCaLE 16x will be dedicated to libre graphics software and artists. All those who work with free and open-source tools for creative graphics projects are invited to submit a proposal and join us for the day!

SCaLE 16x will take place from March 8 to 11 of 2018 in Pasadena California. Libre Graphics Day: SCaLE will take place at the main SCaLE venue on Friday, March 9.

The libre graphics track is an opportunity for teams, contributors and practitioners involved in Libre Graphics projects to share their experiences, showcase new developments, and hear new and inspiring ideas.

By libre graphics we mean “free, Libre and Open Source tools for creative uses”. Libre graphics is not just about software, but extends to standards and file formats used in creative work.

People from around the world who are passionate about Free/Libre tools and their creative applications are encouraged to submit a talk proposal. Sessions will be 30 minutes in length.

Developers, artists, and activists alike are invited. First-time presenters and established projects of all sizes are welcome to submit.

We are looking for:

• Reflections and practical sessions on promoting the philosophy and use of Libre Graphics tools.
• Technical presentations and workshops for developers.
• Showcases of excellent work made using Libre Graphics tools.
• New tools and workflows for graphics and code.
• Reflections on the activities of existing Free/Libre and Open Source communities.

Submit

Please submit your proposal to graphics-cfp@socallinuxexpo.org.

If you have any questions feel free to reach out to me on the forum.

Deadline

The deadline for submissions is January 10th, 2018, and participants will be notified by the end of January 2018.