Color profiles in RT and GIMP

Software RawTherapee
1

Hi,

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

Scenario:

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 https://infophagia.com/ntz/paste/pixls-20240710.tgz ++ 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

2

: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

3

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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4

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

5

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.

6

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

7

To avoid any legal headaches of redistributing copyrighted materials.

8
  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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