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Articles and tutorials on ICC profile color management and free/libre image editing

Ponte de Amazade bridge
Processed with high bit depth GIMP using RGB plate replacement.

The philosophy behind the Nine Degrees Below color management articles and tutorials

Many times, articles on color management assume that all the reader really wants to know is which buttons to push. On this website the first assumption is that you want to understand enough about color management to make your own intelligent decisions.

The second assumption on this website is that you run Linux and use free/libre software. Most articles on the internet that discuss color management assume that you run a proprietary OS and use PhotoShop. Fortunately the principles of color management are the same regardless of which operating system and which software you use. So if you use a proprietary OS and you want to try any of the concrete examples provided in the articles, most free/libre imaging software also runs on Windows and Apple. The only difficulty you might encounter is with some of the command line examples, as the exact syntax does vary slightly from OS to OS.

Why does this website focus exclusively on free-libre image editing software? I have no particular philosophical quarrel with proprietary editing software. But I do object to the idea that the artist's own work should be locked into a proprietary file format such as PhotoShop's PSD. Adobe's move to the cloud has made this issue of who controls access to the artist's work crucially important. The Creative Cloud license agreement itself is onerous and one-sided. Once the artist stops paying the subscription fee, she loses access to the software that unlocks the proprietary PSD format that contains her creative work.

What's on the Nine Degrees Below website?

Painted from a reference photograph using Krita and high bit depth GIMP.

Links to Galleries, About, and the Articles and Tutorials on Color Management and Image Editing

Articles & Tutorials on Color Management and Image Editing has links to all (well, almost all) of the articles and tutorials on this website, arranged by topic. Here is a summary of what's covered — please note that article counts given below for the various topics are not always up-to-date and also don't include articles that for one reason or another aren't yet listed on the Articles page:

  1. Tutorials on Practical ICC Profile Color Management in the Digital Darkroom: If you are a complete newbie to ICC profile color management, or if you think maybe you missed some key concepts along the way, these tutorials can help you figure it all out [9 articles].
  2. Calibrating and profiling your monitor: If your monitor isn't showing you accurate colors, then color management isn't all that useful [4 articles].
  3. ICC RGB Working Spaces: According to the ICC, color management is about ensuring accurate, predictable colors from capture device to final output device. Somehow the ICC totally overlooks the fact that we also edit our images in ICC RGB color spaces . . . which raises the obvious question: Which RGB color spaces are best for image editing?
    1. The infamous sRGB color space [6 articles].
    2. Surveys and specifications [3 articles].
    3. Well Behaved RGB Working Spaces [4 articles].
    4. Choosing an RGB working space [8 articles].
  4. Profiling your digital camera: A custom camera input profile that's also a well-behaved RGB working space can be quite useful for editing purposes. And depending on your camera and what you are photographing, colors in your interpolated raw file might be more accurate and also might look nicer if you make and use your own custom camera input profile [3 articles].
  5. Camera Raw Files has increasingly outdated reviews of free/libre raw processors (that nonetheless have some very useful information — updating these reviews is on my "to do" list); several articles on dcraw code (useful for anyone wanting to know what goes into interpolating a raw file); and some general articles on raw processing, including a "how to" for shooting ev-bracketed raw files (which has some rather pointed criticisms of the Sony A7 line of cameras), and an experiment with using RawTherapee's awesome CIECAM02 module to white balance a raw file [10 articles].
  6. Stacked ev-bracketed raw files for clean shadows and intact highlights (shot using a Sony A7 camera on a tripod, interpolated using PhotoFlow, and processed using high bit depth GIMP).
  7. Digital Asset Management using digiKam and exiftool, containing useful command line examples for ingesting camera files and for examining and modifying metadata (including commands for removing unwanted metadata written by various DAM softwares that insist on writing anything and everything in every conceivable possible location) [3 articles].
  8. High bit depth GIMP 2.10. High bit depth GIMP has been my primary image editor since 2012, when I started contributing to GIMP development, mostly in the areas of color management and color mixing. High bit depth GIMP's floating point processing and very awesome LCh color space operations have transformed the way I approach editing photographs and making digital paintings:
    1. Introductory tutorials on using high bit depth GIMP 2.10 [4 articles].
    2. Using GIMP 2.10's new LCh and Luminance blend modes to edit photographs [4 articles].
    3. Using GIMP's LCh color space and blend modes for painting [5 articles].
    4. Building GIMP from source code [4 articles].
    5. Miscellaneous articles on GIMP [3 articles].
  9. Repaired and converted to black and white, then split-toned (processed using high bit depth GIMP's LCh blend modes).
  10. General articles on painting, photography, and combining painting with photography, which category is intended to be flexible enough to handle "whatever I feel like writing about". [3 articles].

In case you are curious, the About page has a little bit of information about why I switched to using Linux and started the Nine Degrees Below website, along with an explanation of the website name "Nine Degrees Below" (hint: refers to the angle of the sun with respect to the horizon, hence to the midpoint of sunrise and sunset), and the Galleries have a few of my photographs.

If you use free/libre software, then support free/libre software!

Free/libre software doesn't happen by magic. Nope, it's the result of on-going collaborations and contributions, and there are many ways you can help:

PIXLS.US — A new and very different forum for people using and developing free/libre photography and painting software

Free/libre software has many amazing forums and mailing lists for discussing particular softwares, for example the Krita forums and the digiKam, GIMP, and ArgyllCMS mailing lists. These forums and mailing lists are wonderful places to discuss the ins and outs of using the various softwares. But they all have one thing in common: they focus on using one particular software. Since first starting to use free/libre software for image editing I have felt the lack of a forum for discussing image-making issues that transcend using any specific software. Pat David saw this same lack, and unlike me, he actually did something about the situation and started the PIXLS.US website and forums.

Although PIXLS.US initially focused on photographers using free/libre software, Pat realized that digital painters also need a good home for discussions that go beyond how to use specific free/libre softwares. So now PIXLS.US has a forum for digital painting, or speaking more generally, art outside photography. So whether you are a digital photographer, a digital painter, or you make images that don't fit very well within these somewhat constraining categories, head on over to PIXLS.US and introduce yourself — you'll find like-minded people and a nice place to discuss whatever's on your mind (well, at least if it's related to making images using free software, but there's also a forum for discussing topics outside painting and photography).

Free/libre software is a collaborative effort

Free/libre software doesn't write itself, and there are many ways to contribute:

  • Participate in user forums and mailing lists
  • Write bug reports
  • Contribute code
  • Contribute documentation
  • Provide financial support

Whatever way makes you happy, if you use free/libre software, please find a way to support free/libre software.

Two projects that could use some extra help

If you are looking for a way to contribute time, talent, or money to free/libre software, I want to single out two of my favorite free/libre software projects, both of which are crucially important to free/libre image editing:

  • ArgyllCMS needs monetary contributions. ArgyllCMS is the best software there is — free/libre or otherwise — for calibrating and profiling your monitor, printer, and camera. But failing sufficient monetary support from users, Graham Gill may be forced to shut the doors on ArgyllCMS development.
  • GIMP needs programmers. High bit depth GIMP 2.10 is almost here. But there are too few developers. So if you can program and you have a desire to see GIMP morph into the best possible high bit depth image editor, now's a good time to pitch in and help.

    If you use the Windows version of GIMP, here are a couple of cold hard facts: (1)GIMP is a native Linux application; (2)The best way free/libre software that's native to Linux gets ported to and kept running properly on Windows, is if a Windows developer steps up to the plate and takes on the responsibility for porting, building, testing, and fixing Windows-specific bugs for that software. GIMP currently doesn't have any Windows developers, so if you are a Windows developer, now is a great time to pitch in and help.

    If you aren't a programmer, there are many other ways to contribute to GIMP development, such as helping to debug the code (this just means using GIMP and making good bug reports), and helping to update the massive amounts of documentation, especially important as the first official release of GIMP 2.10 draws near.

A Sampling of articles and tutorials on the Nine Degrees Below website

These "summaries with links" are here mostly to give you an idea of what sort of information is on this website. Articles & Tutorials on Color Management and Image Editing (which you can access by clicking on the "Articles" tab at the top of any page on this website) has the full list of Nine Degrees Below articles and tutorials.

  • Profiling Your Monitor — popular confusions, hopefully cleared

    Big changes are taking place in open source color management, including whether, how, and what happens when a system monitor profile is set. The monitor profile your editing software uses determines what you see on your screen. So now is a very good time to learn more about monitor profiles.

    If you are not really sure what the difference is between calibrating and profiling a monitor; if you've heard the words "vcgt tag" but don't know what it means; or if you'd like to know what a system monitor profile is, this article is a place to start.

  • Leaves in May — A tutorial on making an illustration from a photograph.

    This tutorial explains a method for making an illustration rendering from a photograph. One of the steps produces a nice line drawing. So really this is two tutorials in one. I included notes on choosing the right RGB working space for the task at hand. So maybe it's three tutorials in one.

  • White balancing camera-saved sRGB jpegs that were shot using the wrong camera white balance

    sRGB is not the right color space for white balancing camera-saved sRGB jpegs that were shot using the wrong camera white balance setting. Better results can be obtained by editing your images in a linear gamma version of the Rec.2020 color space.

  • How to Make a Better Custom Camera Input Profile that's also an RGB Working Space

    IT8 target chart shot for profiling a camera.This article shows how to use ArgyllCMS and a target chart to make a better general purpose custom camera input profile that is color balanced and normalized. The resulting camera input profile is well behaved and so can also be used as an RGB working space for editing your interpolated raw files.

  • Making a useful LCh color palette

    GIMP color management settings for the color management experiments.This tutorial provides a set of downloadable LCh-based color palettes to use with GIMP-2.10. The color palettes were put together using information from the handprint website. The LCh color wheel provides a useful framework for organizing and choosing colors, and allows to access the treasure-trove of colorimetric color information available on the internet. Links are provided to some nice articles for skin colors and flower colors.

    The last section of this tutorial discusses how it's possible that there could be such a thing as an unprintable color in the very small sRGB color space, and compares results of using HSV Saturation vs LCH Chroma to lower the saturation of colors that are out of gamut with respect to a printer profile: lowering the Chroma produces much nicer results.

  • Color Management Experiment Kit: If seeing is believing, how much does your monitor profile matter?

    GIMP color management settings for the color management experiments.There are two approaches to learning anything: Learn theory and then try to apply it. Or (my preferred approach) start experimenting and worry about theory later.

    This 'Color Management Experiment Kit' is for exploring the difference a monitor profile makes in what you see on your monitor screen. It has ICC monitor profiles to play with, experiments to try, and images to try them on. Think of it as the digital darkroom equivalent of being handed a kid's chemistry set, except the only thing you'll risk blowing up is a few pixels.

  • Limitations of unbounded sRGB as a universal color space for image editing

    Two versions of a car show photograph showing that correcting a color cast in the wrong RGB working space produces wrong results.Unbounded sRGB can be used to encode and display any RGB color. Nonetheless, unbounded sRGB is not suitable for use as a universal, "one size fits all" color space for image editing. Many editing operations are chromaticity dependent, giving different results in different RGB working spaces. Choosing the right working space for the task at hand is the photographer's first, and critically important, technical and artistic decision.

  • Completely Painless Programmer's Guide to XYZ, RGB, ICC, xyY, and TRCs

    ICC profile xicclu and tone response curves.This tutorial was written in the hope that it might be of use to technically savvy people who know a whole lot about the code and the mathematics that goes into making an image editing program, but perhaps not so much about color spaces and ICC profiles. It also serves as a pretty good high-level overview of color science for non-coders.

  • Will the Real sRGB Profile Please Stand Up?

    Temple on a misty day.There's only one sRGB profile, right? Wrong! I compared 15 widely used sRGB matrix profiles distributed by/with a variety of profile vendors and imaging software, and found quite a bit of variation from one sRGB profile to the next. In this article I explore the differences between the sRGB profiles variants and point out the practical digital darkroom consequences.