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If I were to analyze or change an ICC profile embedded in an image, how should I proceed?

I'd also be glad to understand how an "end-user" is able to create these with a tristimulus colorimeter or a spectrophotometer and if/how this new profile can be added to a color capturing device (i.e. a camera).

My curiosity comes from images that were taken by a professional photographer. When I open them in GIMP, there's a pop-up referring "there is an embedded ICC profile" and if I "would like to convert the image to RGB (sRGB built-in)". I always convert all of them before using them, since the colors are slightly improved.

This is the image as it was provided by the photographer: No ICC

And this is after the embedded ICC profile was applied: With ICC

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    $\begingroup$ I would take littlecms.com for a spin $\endgroup$ – joojaa Aug 10 '15 at 15:44
  • $\begingroup$ @joojaa This is great! They actually say: "lcms is a CMM engine; it implements fast transforms between ICC profiles". And by their trial of the professional solution, they provide a lot of options ("input for RGB, Gray, and CMYK spaces", "intents", "destination color space", etc.)... I never imagined that it could be so vast. $\endgroup$ – Armfoot Aug 10 '15 at 16:07
  • $\begingroup$ The international color consortium defines 4 transformation intents for the colors that can not fit the gamut, read the tutorial. $\endgroup$ – joojaa Aug 10 '15 at 16:08
  • $\begingroup$ @joojaa actually, in their own program they have a small description associated to all of the 7 types of "rendering intents" we can choose from when converting. $\endgroup$ – Armfoot Aug 10 '15 at 16:13
  • $\begingroup$ hey allow for more intents and different white point/ blackpoint combinations. (adobe thus has 3*4 intents) $\endgroup$ – joojaa Aug 10 '15 at 16:33
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I realized that littlecms, suggested by joojaa in a comment above is very complete in dealing with the ICC profiles.

I did a few tests in their color translator program with different destination color spaces and the differences are great as you can see:

Original

Original

sRGB-like

sRGB

adobeRGB1998 (it seems it's the original color space)

adobeRGB

appleRGB

apple

And the most desirable results in my case are within the ProPhotoRGB color space:

prophoto

linearProPhotoRGB

linearProPhoto

All of the above were following an automatic rendering intent but other intents bring slight variations (samples applied together with linearProPhotoRGB destination color space):

Absolute Colorimetric

ICC absolute colorimetric

Legacy Unadapted Absolute Colorimetric

Legacy

I also realized that GIMP was actually restoring the original profile (not the opposite as I thought, i.e. instead of applying an embedded ICC profile, it was taking it off) and with this littlecms, now it does seem much simpler to "translate" color spaces than I thought.

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