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

[markanini]

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]

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]

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]

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.