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

[Harry Wentland]

On 2025-01-17 04:06, Pekka Paalanen wrote:
> On Thu, 16 Jan 2025 10:56:22 +0200
> Pekka Paalanen <pekka.paalanen at haloniitty.fi> wrote:
> 
>> On Thu, 19 Dec 2024 21:33:37 -0700
>> Alex Hung <alex.hung at amd.com> wrote:
>>
>>> From: Harry Wentland <harry.wentland at amd.com>
>>>
>>> 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.
>>>
>>> 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).
>>>
>>> Signed-off-by: Alex Hung <alex.hung at amd.com>
>>> Signed-off-by: Harry Wentland <harry.wentland at amd.com>  
>>
>> Hi,
>>
>> why would a display system ever use BT.2020 or BT.709 OETF or its
>> inverse?
> 
> Sorry, this is more for my own curiosity, not an argument against the
> patch. Since hardware designers decided to incorporate these curves
> explicitly, what use was in mind? It's likely something I have
> overlooked.
> 

I'm not entirely sure myself, but gamescope does use it for displaying
game streaming content.

https://github.com/ValveSoftware/gamescope/blob/2f88849ac9dc7da5c678d5d7d3e9b58f38add1bf/src/Backends/DRMBackend.cpp#L2509

Harry

> 
> Thanks,
> pq