Articles & tutorials on color management and photography using free/libre software

Articles and tutorials on color management and photography

Most of the articles and tutorials on this website are about practical color management in the digital darkroom. In addition, you'll find articles on other digital darkroom topics, in particular raw processing and digital asset management, plus the occasional write-up about specific image editing software.

Recent and featured articles

Recent articles

  • User's Guide to High Bit Depth GIMP 2.9

    High bit depth GIMP 2.9 still has a lot of hard-coded sRGB parameters. If you edit images in other RGB working spaces such as AdobeRGB1998 or ProPhotoRGB, all the operations that use these parameters produce incorrect results. This user's guide tells you which editing operations to avoid when editing in wider gamut RGB working spaces and provides workarounds for dealing with issues created by the presence of hard-coded sRGB parameters in the code base.

  • The Sad State of High Bit Depth GIMP Color Management

    Fixing high bit depth GIMP color management before the release of GIMP 2.10 would be relatively simple. But progress is hampered by the fatally flawed (and thankfully not yet fully implemented) babl/GEGL "unbounded sRGB architecture". This "architecture" is based on the absurd premise that slider operations should always produce the same results on colorimetrically the same colors.

  • Models for image editing: Display-referred and scene-referred

    This article explains the similarities and differences between display-referred and scene-referred image editing. Even though the two models serve very different image editing goals, both models work with bounded RGB data. Display-referred RGB data is bounded by Color, which is to say by both Luminance and Chromaticity. Scene-referred RGB data is bounded only by Chromaticity.

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

    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.

  • From sRGB color space to sRGB profile: how to calculate the ICC sRGB profile primaries from the sRGB color space specifications

    This article provides a step-by-step worked example of performing a Bradford chromatic adaptation to calculate the D50-adapted ICC sRGB profile red, green, and blue primaries from the unadapted red, green, blue, and white xyz values given in the sRGB color space specifications.

  • A Review of FLOSS Raw Processors, Part 1 (revised and updated)

    Flat and enhanced raw rendering of a dandelion. Part 1 of a review of free and open source raw processors compares seven free and open source raw processors — dcraw, darktable, the digiKam raw processor, Photivo, Rawstudio, RawTherapee, and UFRaw — "by the specs", without looking at actual interpolated output. This review only considers features relevant to radiometrically correct raw processing and not other features such as image enhancing algorithms or digital asset management.

  • What do Clipped Colors from ICC Profile Conversions really look like?

    A bright red flower with clipped colors in petal highlights. You've been told that converting an image from one color space to another can result in clipped colors. But how, why, and where does the clipping actually happen? This article shows you a real-world example of clipped colors in the image itself, in the image color gamut as seen from inside the CieLAB reference color space, and in the image's individual red, blue, and green channels.

All the articles and tutorials

Articles & Tutorials on Color Management and Photography has links to all the color management and photography articles on this website.

The philosophy behind the articles

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. 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.

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.

My About page has a little bit of information about why I switched to using Linux and started the Nine Degrees Below website, and the Gallery has a few of my photographs.

If you have questions or comments about any of the articles on this website, I'd love to hear from you (even if you run one of those other operating systems 😉). You can reach me at ellestone (at) ninedegreesbelow (dot) com.