Color profiles in RT and GIMP


I’ve been reading a lot about color profiles and still there is a little confusion for me …


Default working profile in RT is ProPhoto while working with RAW and default output profile is RTv4_sRGB which I’ve changed to RTv4_Large … I suppose this is right for further processing in GIMP … Now I am confused on the next steps if I wanted to export file as JPG for presenting on WEB - which I suppose should be in sRGB …

I did a test … Please see files in following archive ++ see README for description on each file

I have few questions:

  1. What should I use as a default combination for a JPG that will be just presented online (not used as a input for a print or further processing) ?

  2. why for the sake of GOD are colours broken (at least in Gwenview - which indicates some issue in general) when I converted to GIMP’s sRGB from RT’s Large but colours are OK when I converted to GIMP’s sRGB from RT’s v4 sRGB - see Screenshot or when I’ve unchecked to include color profile which results in GIMP’s sRGB like if converted … is it some BUG (of GIMP) ?

  3. why are tif files with sRGB and Large of same size o.O ? Is there actually any difference in color gamut in these two tif files … Does it make any sense to export to GIMP with RTv4_Large then ?

Normally I do without thinking

  • I work in RT with default ProPhoto
  • I export for further processing with GIMP with RTv4_Large
  • I retain in GIMP RTv4_Large and don’t convert to GIMP’s built-in sRGB
  • I export from GIMP to JPG using checked `include color profile’ checkbox … Then file is not sRGB ? o.O
  • I save GIMP’s xcf files typically with original profile which is RTv4_Large or RTv4_sRGB (before I’ve switched to Large)

thanks much and regards, ~dan

:smiley: … it’s maybe confusing … in other words - each JPG in tgz archive is created differently and my question is - which JPG is proper and right for general use - for sharing, for publishing on web

On my phone, will pick at the other questions when I get to my computer, but here’s the answer to #3:

Gamut doesn’t affect file size. The colors are encoded into the channel number format, whatever it is, 8 bit, 16 bit, float, etc. Accordingly, larger gamuts fare better in larger containers, at least 16 bit.

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Don’t forget that other programs will not understand what “RTv4” means. Try a more standard sRBG type of profile.

Programs don’t check the name, but the numerical description of the colour space (profile) embedded in the output – if it is there. If there’s no embedded profile, JPGs are interpreted as sRGB. There shouldn’t be large differences between sRGB versions; I never had any issue with RT’s sRGB output.

RT uses for some reason a custom names for color profiles … so for example RTv4_Large is equivalent of ProPhoto and RTv4_sRGB should be just fancy named sRGB

To avoid any legal headaches of redistributing copyrighted materials.

  1. sRGB unless you have special requirements.
  2. Gwenview is probably picking something up from the EXIF metadata.
  3. Glenn’s answer is correct.

If I used a program that uses the profile name instead of the profile itself, I would not give it any images other than those encoded in sRGB or a compatible color space such as RTv4_sRGB. Programs with poor or non-existent color management usually play best with sRGB.

Not just fancy named. The profile is fancy too. From RawPedia:

RTv4_sRGB is a higher quality version of the standard sRGB profile, which surprisingly is inconsistent between implementations. RTv4_sRGB was custom-made for RawTherapee and has 4096 LUT points, as opposed to the lower quality 1024 point sRGB profiles.

(Emphasis is not mine.)

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