On Wed, 28 Apr 2021 13:24:27 +0530 Shashank Sharma <shashank.sharma@xxxxxxx> 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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