It’s a long one, sorry.
It wasn’t what you said, it was how you said it. But I understand that you and the other knowledgeable people on the forum get lots of questions; some repeated, and surely most way below the level that’s interesting to you. Also, I sometimes fail to remain patient when people ask me or make stupid mistakes, so I can understand your side of the situation, too.
Anyway, I am grateful for your work: both the development and the education (I have also taught software engineers, and know how much time and energy go into even the simplest demos, let away video tutorials).
I think I do understand what a histogram is for; but, like some others, for a long time I simply edited JPGs in the Gimp and similar tools, where I never had to think about colour spaces. Even in RawTherapee (which was my first raw developer, back in the days of Gábor Horváth, who started the project), you could not (at that time; not sure about now) switch the colour space for histograms. In fact, it is a relatively new feature in darktable, too.
Exactly because normally I’m not a ‘gamut freak’ (and I only use sRGB and the display for output, never print), I never really checked the options for soft proofing and gamut check (my general attitude being ‘use the defaults set up by the experts unless you know what they do and know why and how to change them’). Then came your video about the new colour calibration module (‘shiny new stuff’ - and yes, I did use it on some Christmas lights, so I appreciate it a lot!). When you fought the red carpet (https://youtu.be/U4CEN0JPcoM?t=2081), I did not see artefacts in the carpet’s surface (maybe it’s me, maybe Youtube, maybe my monitor), but you did turn on the gamut check and switched the soft-proof profile from the default sRGB (you explained that from https://youtu.be/U4CEN0JPcoM?t=2135 up to about 36:50). I have now re-watched that and re-read Color calibration test and some thoughts - #14 by aurelienpierre (‘color profiles and chromatic adaptation may push colors out of visible spectrum’), and Color calibration test and some thoughts - #19 by aurelienpierre (’ we handle gamut mapping in color calibration only to cleanup after the chromatic adaptation because we know it will push colors out of the visible gamut’) where you answer the question perfectly. So that part is now clear.
I’m still puzzled about the validity (or maybe applicability/relevance to my use case) of the PQ Rec2020 histogram, even with the comment ‘The PQ curve from Rec 2020 PQ dilates shadows a lot and compresses highlights, so it gives you better legibility near black’, as it seems to indicate the photo does not make use of the darkest tones, while the HLG histogram actually indicates clipping in the darks (there’s a minor spike on the left end). Do the two spaces have different black points, or do I misunderstand something? (I’ll just continue to use the default sRGB, I think.)
Thanks,
Kofa