On the internet are many places to download ICC profiles, which promise to implement standards. But how reliable are these profiles and why should users and distributors care about their quality?
Why quality counts? For many users is real value in reliable colour space definitions. Most professionals and advanced amateurs know that wrongly implemented colorimetry can cause them unwanted modifications and will sum up over repeated conversions and colour space assignments until the error has rendered the colour material useless. But profile conformance to the standard, which these profiles claim to represent, is not so obvious. A profile checker can only detect conformance to the ICC standard itself, which is about the file format, but not about the quality of the encoded data.
The preferred solution for professionals is to download ICC profiles only from trusted vendors. Unfortunately for the open source community, most ICC profiles for common standards are restrictively licensed and allow no modifications. However these licenses are a reaction to people, who want to push stuff at whim and fake profile names. After all spreading low quality fakes will mostly harm users. Such faked profile made it in many open source packages. It would help the open source community, if vendors license their ICC profiles for standard conditions after the new non restrictive ICC profile license. Then faking profiles, by the reasoning of providing them under a free license, would not be needed any more.
We have some free and accurate profiles available. Over the past years colour experts have created precise profiles with a free license. Among these profiles are implementations of sRGB, AdobeRGB spec and after a license switch for LStar-RGB and many standard printing conditions. These profiles are packaged in the icc-profiles-openicc data set.
How to check ICC profiles for standards?One indirect method is comparing reference ICC profiles with alternative ones. A visual comparison is possible on Linux with the free CinéPaint and the separate ICC Examin plugin in CIE*Lab space. The above video compares visually the ROMM ICC profile, which shares its colorimetry with ProPhoto RGB, with the Scarse ProPhoto.icm. The Scarse colour value interpretation shows quite some deviation from the Adobe version. To repeat the test: open a test image and assign the ISO 22028-2 ROMM RGB profile. Then open the ICC Examin colour viewer from CinéPaint´s main menu > Image > Watch Colours 3D … The plugin should launch and show you the colour space with the image colours represented as big dots. You can change the dot size in ICC Examin with the ‘+’ and ‘-’ keys. Then assign the Scarse Kodak ProPhoto RGB to the image from main menu > Image > Assign ICC Profile … The colour dots change to the new interpretation by the lcms CMM after assigning. A unwanted deviation in the interpretation is marked by a line. That visual method of inspecting line vectors is much easier than comparing colour differences directly. Possible rendering intents for these kind of comparisons are relative colorimetric and absolute colorimetric, as these are well defined by the ICC spec. Disadvantages of the outlined method are the need of reference profiles in the first place and so far no numerical results.