[CSC-SDR]Source TRC can't be changed

dantmnf / MHC2

information about next generation color management in Windows

The Unlicense

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[CSC-SDR]Source TRC can't be changed #6

Open markanini opened 1 year ago

markanini commented 1 year ago

SDR-CSC generation yields an output that matches sRGB TRC with default settings. When I desired a gamma 2.2 TRC* I tried the --source-gamut-icc command and sprovided a synthetic profile with sRGB primaries and gamma 2.2 TRC. My expectation was that the resulting output would change from default, but it didn't.

(*) or something close what I got when selecting gamma 2.2 in novideo_srgb https://hub-assets.displaycal.net/wp-content/uploads/users/mark-wilhelmsson/2022/03/24/Measurement-Report-3.8.9.3-%E2%80%94-24G2W1G4-@-0-0-1920x1080-%E2%80%94-2022-03-24-10-13.html

Source sRGB-2.2v2.zip CSC sRGB3.zip

dantmnf commented 1 year ago

I do have some tests on gamma 2.2 source TRC and it turns out that source TRC in the pipeline is fixed to sRGB and is not programmable by the user^1.

Think of this scenario:

a random ICC-aware app outputs content encoded in gamma 2.2 (as per ICC profile)
Windows applies sRGB degamma function
attempts to do some linear transform
... everything messes up

markanini commented 1 year ago

Thanks for the info. Do you think that line of thinking breaks down when viewing it as retroactively forcing compliance for a vast amount of untagged content based on a standard created with CRT tech in mind?

Assuming sRGB TRC

Handles the condition of sRGB content that's not properly tagged or embedded with the correct profile. Relatively rare.
Not fully accurate or visually pleasing on current flat panel tech with non-zero blacks.
Remains non-compliant to the original spec of 80 cdm2 white level(for good reason it's unrestricted. Gamma 2.2 is the logical next step).

Assuming gamma 2.2 TRC

Matches the default target of most calibrator software.
Represents native output of current display tech better, therefor less rounding errors as a result and closer to conditions of content created on non-color managed setups.

dantmnf commented 1 year ago

Do you think that line of thinking breaks down when viewing it as retroactively forcing compliance for a vast amount of untagged content based on a standard created with CRT tech in mind?

Yes but … I can't control it. ¯\_(ツ)_/¯

Unlike novideo_srgb which has full control over the degamma-matrix-regamma pipeline, the MHC2 pipeline only has access to the matrix and regamma part. The only thing we can do is to make ICC-aware apps match the fixed degamma behavior.