Haldcluts and color spaces

One question. The behaviour of the Film Simulation and the local adjustments when you load a haldclut is the same as it is in Rawtherapee?. Focusing in color spaces.

I have this from Alberto. It is correct?

" agriggio commented on Dec 7, 2018.

This is sort of expected. If the CLUT name ends with a working profile name, that is stripped off, and used as the colour space for applying the CLUT. The logic is more or less as follows.
If you have a CLUT called MyClut_ProPhoto, it will show up as MyClut_, and the image will be converted to ProPhoto when applying the clut. Something like this:

convert image from working space to ProPhoto
apply sRGB gamma
apply clut
apply inverse sRGB gamma
convert back to working space

I don’t know why sRGB gamma is always applied, but, alas, that’s what happens (if I understand the code correctly)."


That’s correct, yes, for haldcluts. CLF luts and CTL scripts work differently, as explained here.


So… ART internally converts the image to sRGB if you don´t add “_(the working profile)” to the name of the haldclut? Correct?

Two examples. Always with ProPhoto as working profile in ART.

Then… if i have made a lut for Prophoto images for example… i would choose to add “_ProPhoto” to the name of the clut. And if my lut is made for sRGB images i would not add anything because ART expect, if you don´t tell to it, a lut based in sRGB tranformations. Correct again?

Yes, correct


To clarify. I don´t wanna be boring but it is my dilemma…

I have a RAW photo. All my photos will end with an AdobeRGB gamut, choising in ART this profile to render the image at the end of the pipeline. The working profile will be Prophoto.
If i don´t want to compress the color gamut of my image because of the internally conversion in ART to sRGB in the Haldclut stage… i should make/ prepare / convert my lut to AdobeRGB to represent correctly the transformation AND to name the haldclut file with “_Adobe RGB” to tell ART not to make any conversion into sRGB. This way i get a correct transformation without the sRGB tranformation ART makes if you don´t tell anything via file name.

I hope i have understood all in a proper way.

In my example… Art applies muy lut working with the gamma and color characteristics of AdobeRGB, transforms internally the image to AdobeRGB to apply it. Then ART converts again my image to the working profile (Prophoto) to continue with the rest of the tools in that space. Meanwhile i get my image not to be reduced to sRGB color gamut representation, it has been constricted to a wider AdobeRGB gamut, that is the final space i will use to output.

Thanks for reading again!

Yes, correct. Just append Adobe RGB to the file name to let ART know that this is the colour space (*) the lut expects. Note that both the capitalization and the space are important.

(*) Technically, only the primaries of the colour space (the white point is always D50, and the trc is the srgb one)

Is the sRGB gamma being applied so the LUT is applied in linear space?

No ( if I understood the question)

I was worried about the primaries. About TRC, i had it very clear… but i had not thinked about the iluminant.

Thank you very much agriggio !

Is there color space name list for luts?

I’ll try to compile one (unless the info is already in rawpedia? I have to check…). However, if you are concerned about this, I’d suggest to consider using CLF luts, which give you all the control you want

What luts are you talking about? The haldclut luts from Rawtherapee?

I think they were made with sRGB primaries in mind. Maybe i am wrong, but i think so.

Alberto was referencing to this: CLF LUTs in ART

Oh yes. OCIO luts. But there was a question from Yasuo in first place.


By the way… An interesting reading…


@Urtaur I’m not sure who the question was for, sorry…

My fault, and my poor english. Don´t worry. I was trying to understand what luts were you talking about you and Yasuo. He (Yasuo) asked about a color space name list. That´s all.