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I have seen references to two versions of sRGB v2

  • IEC 6 1966-2-1, for example here
  • ICC.1: 2001-04, for example here

Are these the same, or different? They come from 2 different organizations (IEC=International Electrotechnical Commission, ICC=International Color Consortium) and seem to reference 2 different years, 1966 and 2001. I believe these are both "v2" and neither is "v4" of sRGB, but let me know if that's wrong.

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You list different things. The 2001 reference is an ICC Specification that defines how V2 profiles are structured. The specification applies to profiles such as sRGB as well as others such as ProPhoto RGB and even printer profiles.

The 1966-2-1 is not a year. It's a profile description document number and does specify sRGB which was created jointly by HP and Microsoft.

Profile version standards are established by the ICC and ISO. These define how a given profile's internal tables should be used mathematically.

Version 2 profiles are compatible with Version 4 profiles. Version 4 sRGB profiles may, but are not required to, implement gamut mapping in Perceptual transforms but there has been no wide use of this feature so far.

You can go to www.color.org for detailed specs, white papers, and get downloadable sRGB profiles. The 1966-2-1 version dominates and is the standard in Adobe and most other products. Some manufacturers supply their own as well but all the ones I've looked at are indistinguishable outside of invisible rounding errors. One can also get at www.color.org a profile examination utility that lets you look at the guts in profiles.

http://www.color.org/srgbprofiles.xalter

  • Very helpful, thanks. For some calculations, I would like to make sure that I am using sRGB V2 consistently. Here it states that there are 5 (!) types of sRGB V2 depending on the rendering intent, color.org/ICC_White_Paper_26_Using_the_V4_sRGB_ICC_profile.pdf I want to make sure I am using the exact same type of sRGB V2. If I choose sRGB IEC 6 1966-2-1 V2 with Absolute rendering intent in all my calculations, there is no ambiguity, right? i.e. I have fully specified the color space and there can be no mixup with another? – KAE Apr 25 '18 at 21:20
  • The 1966-2-1 sRGB profile does have an issue with Absolute Colorimetric conversions/rendering. This was due to earlier misunderstandings about whether colors should be adapted to D50 or not. The ICC then clarified that display colors using D65 should be numerically adapted to D50. This gets complicated but Adobe's ACE CMM (the default) properly adapts whereas Microsofts ICM does not. This shows up if you convert to a colorspace with a media white point of D50 which will significantly tint the image toward blue. This problem only shows up doing conversions to/from Abs. Col. with Msofts ICM. – doug Apr 25 '18 at 22:12
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    This confusion goes back to a difference between how the CIE v ICC defines Absolute Colorimetric. The ICC says Abs. should be adapted to D50 regardless of the media white point. This may seem odd but it keeps soft proofing, which requires Abs., working even when a monitor is profiles for some other white point such as D65 or D75. – doug Apr 25 '18 at 22:18

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