P3 profile types, practical tips about usages

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    Tamas Toth (ebola)
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    Dear Florian!

    Half year ago I bought one LG – UltraFine 24″ monitor with 98% P3 gamut. While I calibrated it with my SpyderX on Ubuntu 20.04 and the result seemed correct yesterday was the first day when I was tried to use those images what I edited in Darktable in the last some months with the ‘new’ monitor and got som interesting questions. Sorry for asking for your time but you are the only perfect person who can answer my ‘problems’.

    I calibrated the monitor with sRGB transport curve to 6504K whitepoint (as I’m a big D65 fan to avoid unneeded warmth) as I saw on some articles that DCI P3 and D65 P3 generally use 2.6 gamma curve (originally for theaters) what could be not really perfect for monitors and this is why Apple defined the Display P3 with D66 WP and sRGB transport curve (and because some backward compatibility).

    The result is fine, seems no problems. But here is the interesting part of it. Latest Darktable has it’s own PQ P3 and HLG P3 profiles. I tried to search for these to thingies and got answers that both of these 2 profiles use P3 gamma but with different transport curve. PQ usually for Dolby encoded/decoded materials while HGL has a hybrid curve with sRGB like lower luminous intensity ‘half’ and logarithmic like upper luminous intensity ‘half’. This latter is also for compatibility reasons (as Apple does with Display P3). Until here seems I understand the background (at least I hoped). As my goal with the sRGB transport curve was to reach something Display/HLG like results I tried to check it under Darktable with soft-proof with the available PQ and HLG P3 profiles.

    Soft-proofing my sRGB curved P3 display profile to PQ P3 gave me a slightly darker colors in dark parts of images.
    Soft-proofing my sRGB curved P3 display profile to HLG P3 gave me almost no difference.

    Ok. If HLG P3 also uses sRGB like curve in the dark areas seems these 2 soft-proof examples confirm (I mean the results of them) that my calibration is fine. Ok., so in the future I could use this HLG P3 profile (as an almost standard profile) on my exported images (if I want to ‘limit’ all further image viewings to my desired settings). Fine.

    And at this point in Darktable I simply checked some simply sRGB color profile soft-proof on the same images and the results scared me. With sRGB soft-proof I got almost the same slightly dark colors in the dark areas of the images as I saw with PQ P3 soft-proofing. If the HLG P3 uses sRGB curves in dark areas, and my monitor calibrated to sRGB curve and the standard sRGB color profile of course uses also sRGB transport curve how could be the soft-proof result on sRGB color profile different as my own (and what based on the above informations seems the same as HLG P3)?

    How the standard sRGB color profile has different luminance dynamic as my sRGB transport curve calibrated (P3) monitor? If the answer is that maybe my monitor could not totally reproduce the sRGB tone curve (as this is an LCD monitor while sRGB color space birthed in CRT world) how could be the same as HLG P3? And at this point my question also that how could calibrate my monitor to get same results handling luminance as almost the whole world with standard sRGB monitors? The difference is not huge, really slightly but visible and I totally lost in the whole background logic also. iF my monitor calibrated to sRGB curve why PQ P3 soft-proofing give a same results as soft-proof of standard sRGB color profile (and why not HLG P3 is the same as the standard sRGB color profile)?

    Thank you very much in advance if you have some time to explain me my misunderstand!


    (Ps.: As the spec of the monitor tells: Color Gamut (Typ.) DCI-P3 98% (CIE1976) Is it mention in theory that I could use gamma 2.6 on it? As DCI-P3 has gamma 2.6 transport curve.)

    SpyderX Pro on Amazon  
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    Tamas Toth (ebola)
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    Hi! I made some more tests so here are the results:

    As I found that Argyll ‘install’ one Display P3 profile into it’s references/profiles dir, I checked that also. That Display P3 behave the same as PQ P3 what is based on my informations interesting as Display P3 could behave like HLG P3.

    So Argyll’s Display P3 profile give me slightly darker dark ares on my test image.

    But now I check lot more images then I did on weekend and I got that the difference is really just very slight. On the most of my images I could not bring up it and if my eyes not wrong the difference usually visible just in very dark green areas. On dark reds, or blues not, just on greens.

    I also got as result that on some images the HLG, PQ, and Display P3 soft-proofing give me a slightly brighter result on turquoise areas, and some coral like color areas. But just on that colors just some very saturated areas and all 3 profiles behave same like… unlike my another test image where I got darker dark areas with soft-proofed PQ, and Display P3 profiles.

    I simply not understand the background and logic now but I’m know that usually I can notice lot more barely visible differences/problems than usual people do so I really need to drop my perfectionism to live a normal and problemless life:)

    Anyway if Florian, you could explain what happens around me I would be more than happy about it.

    Thanks in advance!


    Tamas Toth (ebola)
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    Dear @fhoech!

    Do you have any opinions on my question? Or anybody who can see any problems in my thoughts and/or have lot more deep technology informations as I have?

    Really not a critical problem but I’m very sad that I do not know the background of the problem.

    Very lot of thanks in advance for any type of answer!

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