RawTherapee to GIMP: Keep RTv4_sRGB or convert to GIMP built-in sRGB?

When opening TIFF (16-bit integer) files from RawTherapee 5.7 saved with RTv4_sRGB as the output profile, should I be keeping that profile or should I be converting to the GIMP built-in sRGB color profile?

I am using GIMP 2.10.14.

These images will eventually be exported to jpeg with an embedded sRGB profile (“Save color profile” checked in the Export Image dialog box).

I seem to recall that there were issues in GIMP whereby using the GIMP built-in profile was recommended but wonder if that’s still true today.

I’ve been keeping RawTherapee’s profile (actually RTv2_sRGB until very recently) but I still feel uneasy that I might be doing the wrong thing.

Any suggestions? Thanks!

Two things:

  1. If possible, you should find a larger-gamut profile to convert in RawTherapee when saving the TIFF. sRGB is too small…
  2. I’m a proponent of minimizing the total number of things done to an image before making the final rendition. Whatever profile the TIFF is in when opened in GIMP, keep it in that, don’t do another conversion…

A mechanic’s musings; wait for the big heads to weigh in… :smile:

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I see that I was making a foolish mistake with the restrictive sRGB choice. I understand. Thanks for catching that!

I just looked at the output profile choices in RawTherapee and see that the choices now do not exactly match those described in RawPedia.

RawPedia describes three of the included output profiles as being similar to ProPhoto: RT_Large_gsRGB, RT_Large_gBT709, and RT_Large_g10. They have differences in gamma.

The similar current choices in RawTherapee, based on the naming, are ones called RTv2_Large and RTv4_Large. I’m guessing they are similar to ProPhoto with a gamma similar to sRGB, with the difference between them being the ICC version.

Will need to investigate.

No foolish mistake, this is not a straightforward topic…

Now I’ll go out a bit on a limb, because I don’t use RawTherapee regularly. My intuition would lead me to use the gamma 1.0 profile, as it will retain the tonal relationship of the RT internal image. Gamma transform isn’t really needed until output of the final rendition, if the medium requires it.

@Morgan_Hardwood, your turn… :smile:

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It might be different now, but my impression is that RTv4_sRGB is better behaved than GIMP’s. Moreover, if you are so inclined, RT has a tool to make your own profile.

I tend to use @Elle’s Rec2020-elle-V4-g10.icc myself.

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Hey

I don’t know what GIMP’s built-in sRGB profile is or does so I can’t comment about that part. However, I can say a few words on RT’s profiles and on the general approach.

Which profile should you use when exporting from RawTherapee? Depends. RawTherapee makes precise color manipulation easy, while GIMP makes me feel like I’m knitting wearing motorcycle gloves. So I avoid doing any color work in GIMP and use it only to remove dust and scratches and such. If this is you, if you’re not using a wide-gamut monitor and if your final image is to be in sRGB, then export from RawTherapee using sRGB (RTv4_sRGB) and save yourself some hassle. Otherwise enter color management hell - here’s a sharp stick and a lighter, good luck.

If you’re exporting from RawTherapee using a color space larger than sRGB because you have a good need for doing so or because you hate yourself, then you should also be using a higher bit-depth format, e.g 16-bit TIFF or 16-bit PNG.

The color management page in RawPedia is not up to date - it is on my long TODO list.

Notice that RawTherapee now comes with an ICC profile creator, so if you need a profile we don’t ship you can easily generate your own, e.g. using ProPhoto primaries and a linear gamma.

As to the question of ICC v2 vs v4, there was a long debate between experts regarding this. No conclusion was reached, but no one was hurt either.

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Thanks for weighing in, shade-tree-mechanic here (me, not OP) just has just enough experience to be dangerous… :smile:

However, even if exporting in sRGB, isn’t it prudent to do so in 16-bit? Sure, GIMP will load 8-bit image files into whatever internal container (>8-bit, floating point, etc), but that crush to 8-bit in the export loses precision that would be a good starting point for pushing the data around in GIMP, no?

I rarely use GIMP for anything other than retouching. I take the full-size image from RawTherapee, retouch using mostly the Healing and Clone tools, resize using Scale Image, sharpen using Richardson-Lucy or Unsharp Mask in G’MIC-Qt, and then export to JPEG.

Yeah, I can see where there might be a trade-off here in which way to go.

If you use G’MIC-Qt, you are better off using sRGB (I prefer RTv4_sRGB) and 16 bit depth. The plugin generally assumes sRGB with 0-255 range. Gamma-wise, it is mostly linear but sometimes standard sRGB, which can be confusing. In the case of RL and unsharp, the filters should be linear sRGB.

My filters (except for 3) accept linear sRGB and any range.

In any case, proper software and hardware colour management via profiles, settings, conversions and bit depth is vital to the post-processing workflow.

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@ggbutcher absolutely yes.