Re: [V7 31/45] drm/colorop: add BT2020/BT709 OETF and Inverse OETF

[Harry Wentland]

On 2025-01-15 03:04, Simon Ser wrote:
>> The BT.709 and BT.2020 OETFs are the same, the only difference
>> being that the BT.2020 variant is defined with more precision
>> for 10 and 12-bit per color encodings.
> 
> Just to make sure, the spec defines this precision, correct? It's
> not an AMD-specific thing?
> 

Yes, see [1]

>> Both are used as encoding functions for video content, and are
>> therefore defined as OETF (opto-electronic transfer function)
>> instead of as EOTF (electro-optical transfer function).
> 
> Ah, and IIRC the OETF is not the mathematical inverse of the EOTF,
> right? So it makes sense to have separate entries for EOTF and OETF
> and their mathematical inverses.
> 

Correct. EOTF and OETF are used for reciprocal purposes but they're
not necessarily inverses of each other. Some curves are defined as
EOTF and others as OETF.

> Again, I am no HDR expert.

No worries. One would think this isn't rocket science but when
looking at it closely it doesn't seem too far off. Granted, I'm
neither a rocket scientist nor an HDR expert, so what do I know. :D

[1] https://en.wikipedia.org/wiki/Rec._2020#Transfer_characteristics

Harry