I’m trying to sort out which colour profiles I should be using. I’m on Linux, editing primarily in RawTherapee, sometimes with additional work in Gimp. I have an older FLATRON IPS235 monitor.
The Rawpedia says I need a wide gamut monitor to use a wide gamut profile, which I think includes ProPhoto (which I have downloaded), or the built-in RTv4_Large. Does this mean I should stick to RTv4_sRGB?
Related, Astbury’s video recommends ProPhoto for the output profile, but includes the caveat “Only do this if you want to use and maintain a fully ProPhotoRGB workflow between RawTherapee,
Photoshop, and Lightroom.” I don’t know if that means it would be a bad thing to use ProPhoto with Gimp, or it just wouldn’t matter?
In general, it is good to edit photos in a larger-than-necessary colour space. Doing so helps reduce artifacts and banding. However, transforming the space to one with a smaller gamut can present issues such as the above and colour shifts.
In recent years, a few raw processors transitioned to Rec. 2020 as the working profile to alleviate transform issues, i.e., it is only slightly larger than the sRGB space but large enough for operations.
As for RTv4_Large, which is the analog of ProPhoto, ask yourself how the final photo will be appreciated. If it is for web or general display, sRGB is your best bet.
PS - The recommended workflow in GIMP would be:
Load image.
Ensure profile is noted; if not, assign profile.
Convert profile before editing.
Optional gamut compression.
Convert profile back to original profile after editing.
Ideally, you should be using a display profile that is calibrated to the display. But, that requires a colorimeter to make one, an expenditure that can be hard to swallow. In that case, you want to use one of the export profiles that’s closest to your monitor’s capabilities. This can be made easy if your monitor has a mode that locks it one of the gamuts, e.g., sRGB. If you set your monitor to that mode, you can use a sRGB profile for the display profile. I made calibrated profiles for all the monitors on my desktop, but I use a sRGB profile on my tablet, mainly too lazy to measure it. Works just fine…
When you save a JPEG or other output, you want to embed a color profile that corresponds to the image data in the file. In most software, when you specify an ‘export profile’, it’ll use that profile to convert the image data as well as embed it in the file. With that, any color managed viewer will have the information to transform the image to the specific capabilities of the connected display.
Alternative to Elle’s profiles, you may use or even build ones out of RT directly. To make custom profiles, follow the instructions in the link: ICC Profile Creator - RawPedia.
I did get a colorimeter years ago, I think I still have it. I’m not sure I ever got it to work with Linux. I’ll have to see what I can figure out about my monitor;.
Sorry, my mistake. I was asking about how to mange colour profiles when sending images from RT to Gimp, so I thought your workflow included both programs.
When using a color managed image editor, there are four possible profiles involved:
The profile for the input files encoding. Hopefully it is in the file as a tag.
The working space the editor converts the image to for editing, when editing in RGB or a derived device space.
The profile describing the colorspace the output file is saved in. This may be the same as the first profile. Hopefully the file will also be tagged with that profile.
The profile that corresponds to the behavior of your display.
The first 3 may well be standard colorspaces (i.e. sRGB, AdobeRGB, ProPhoto, Rec2020 etc.).
In general your display profile is not one of them - each display will be a bit different,
and can certainly be adjusted in different ways. Hence display calibration and profiling.
Some displays may be calibrated to emulate a standard colorspace in the factory to
a degree of accuracy that you can use a standard profile for your display. You at least
have to make sure your display is set to emulate that standard space if you do that.
If you are using wide gamut spaces for any of the first three profiles, then ideally you
should be using a wide gamut display with the appropriate & accurate profile for it
as the 4th profile above.
Note that a number of the standard colorspaces are not reproducible in full on any practical display - i.e. ProPhoto, Rec2020.
Nice clear summary. Just for clarity I’d add there’s actually there’s sometimes a fifth profile involved: A soft-proofing profile which will simulate the final appearance after being sent to a printer, plotter or some other output device (other than the display monitor) under the constraints of that device’s gamut limitations.
Yup, ideally, but it’s possible to do without - just need to be more careful to test your output images on the intended display.
(Why not use that display for editing? Because Linux doesn’t directly support outputting Rec.2020 HLG with appropriate frame metadata in anything but kmsdrm sessions. So it’s edit, export, convert to 10-bit H.265, test on TV for me for now for some workflows…)
Works just fine…