[RFC PATCH 0/3] A drm_plane API to support HDR planes
Pekka Paalanen
ppaalanen at gmail.com
Fri Apr 30 09:43:58 UTC 2021
On Wed, 28 Apr 2021 13:24:27 +0530
Shashank Sharma <shashank.sharma at amd.com> wrote:
> Assuming these details, A compositor will look for DRM color properties like these:
>
> 1. Degamma plane property : To make buffers linear for Gamut mapping
>
> 2. Gamut mapping plane property: To gamut map SRGB buffer to BT2020 colorspace
>
> 3. Color space conversion plane property: To convert from YCBCR->RGB
>
> 4. Tone mapping plane property: To tone map SDR buffer S2H and HDR buffer H2H
>
> 5. Gamma plane/CRTC property: to re-apply the output ST2084 curve
>
>
...
> *
> *
> *
> * ┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐ ┌────────────────┐
> * HDR 600 Nits│ │HDR 600 Nits │ │HDR600 │ │HDR500 │ │ HDR500
> * ────────► │ Degamma ├────────────►│ Color space ├──────────►│ Tone mapping ├──────►│ Gamma │
> * BT2020 │ OETF ST2084 │ BT2020 │ conversion │BT2020 │ H2H │BT2020 │ ST2084 │ BT2020
> * YCBCR420 │ │ YCBCR420 │ YCBCR->RGB │RGB88 │ 600->500 │RGB888 │ │ RGB888
> * Non Linear └─────────────────┘ Linear └─────────────────┘Linear └─────────────────┘Linear └────────────────┘ ST2084
> */
Hi Shashank,
I think you might have degamma and color model conversion reversed, or
is that a new thing in the HDR specs?
Usually the YCbCr/RGB conversion matrix applies to non-linear values
AFAIU.
There is also confusion with OETF vs. EOTF. I got that initially wrong
too. OETF is not just a name for inverse-EOTF but it is used in a
different context. Though here it seems to be just a typo.
OETF is inherent to a camera when it converts light into
electrical signals. EOTF is inherent to a monitor when it converts
electrical signals to light. Depending on what the electrical signals
have been defined to be in each step of a broadcasting chain, you might
need OETF or EOTF or their inverse or a different OETF or EOTF or their
inverse.
As we are talking about displays and likely assuming display-referred
content (not scene-referred content), we probably have no use for OETF,
but we could have several different EOTFs.
Thanks,
pq
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