On 2023-09-29 03:35, Pekka Paalanen wrote: > On Thu, 28 Sep 2023 16:16:57 -0400 > Harry Wentland <harry.wentland@xxxxxxx> wrote: > >> On 2023-09-25 15:49, Melissa Wen wrote: >>> Brief documentation about pre-defined transfer function usage on AMD >>> display driver and standardized EOTFs and inverse EOTFs. >>> >>> v3: >>> - Document BT709 OETF (Pekka) >>> - Fix description of sRGB and pure power funcs (Pekka) >>> >>> Co-developed-by: Harry Wentland <harry.wentland@xxxxxxx> >>> Signed-off-by: Harry Wentland <harry.wentland@xxxxxxx> >>> Signed-off-by: Melissa Wen <mwen@xxxxxxxxxx> >>> --- >>> .../amd/display/amdgpu_dm/amdgpu_dm_color.c | 39 +++++++++++++++++++ >>> 1 file changed, 39 insertions(+) >>> >>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c >>> index d03bdb010e8b..14f9c02539c6 100644 >>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c >>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c >>> @@ -85,6 +85,45 @@ void amdgpu_dm_init_color_mod(void) >>> } >>> >>> #ifdef AMD_PRIVATE_COLOR >>> +/* Pre-defined Transfer Functions (TF) >>> + * >>> + * AMD driver supports pre-defined mathematical functions for transferring >>> + * between encoded values and optical/linear space. Depending on HW color caps, >>> + * ROMs and curves built by the AMD color module support these transforms. >>> + * >>> + * The driver-specific color implementation exposes properties for pre-blending >>> + * degamma TF, shaper TF (before 3D LUT), and blend(dpp.ogam) TF and >>> + * post-blending regamma (mpc.ogam) TF. However, only pre-blending degamma >>> + * supports ROM curves. AMD color module uses pre-defined coefficients to build >>> + * curves for the other blocks. What can be done by each color block is >>> + * described by struct dpp_color_capsand struct mpc_color_caps. >>> + * >>> + * AMD driver-specific color API exposes the following pre-defined transfer >>> + * functions: >>> + * >>> + * - Linear/Unity: linear/identity relationship between pixel value and >>> + * luminance value; >>> + * - Gamma 2.2, Gamma 2.4, Gamma 2.6: pure power functions; >>> + * - sRGB: 2.4: The piece-wise transfer function from IEC 61966-2-1:1999; >>> + * - BT.709: has a linear segment in the bottom part and then a power function >>> + * with a 0.45 (~1/2.22) gamma for the rest of the range; standardized by >>> + * ITU-R BT.709-6; >>> + * - PQ (Perceptual Quantizer): used for HDR display, allows luminance range >>> + * capability of 0 to 10,000 nits; standardized by SMPTE ST 2084. >>> + * >> >> I think it's important to highlight that the AMD color model is >> designed with an assumption that SDR (sRGB, BT.709, G2.2, etc.) >> peak white maps (normalized to 1.0 FP) to 80 nits in the PQ system. >> This has the implication that PQ EOTF (NL-to-L) maps to [0.0..125.0]. >> 125.0 = 10,000 nits / 80 nits >> >> I think we'll want table or some other way describing this: >> >> (Using L to mean linear and NL to mean non-linear.) >> >> == sRGB, BT709, Gamma 2.x == >> NL form is either UNORM or [0.0, 1.0] >> L form is [0.0, 1.0] >> >> Note that HDR multiplier can wide range beyond [0.0, 1.0]. >> In practice this means that PQ TF is needed for any subsequent >> L-to-NL transforms. >> >> == PQ == >> NL form is either UNORM or FP16 CCCS (Windows canonical composition color space, see [1]) >> L form is [0.0, 125.0] > > Hi, > > what is [1]? > Oops. [1] https://learn.microsoft.com/en-us/windows/win32/direct3darticles/high-dynamic-range Harry > > Thanks, > pq > >> == Unity, Default == >> NL form is either UNORM or FP16 CCCS >> L form is either [0.0, 1.0] (mapping from UNORM) or CCCS (mapping from CCCS FP16) >> >> Harry >> >>> + * In the driver-specific API, color block names attached to TF properties >>> + * suggest the intention regarding non-linear encoding pixel's luminance >>> + * values. As some newer encodings don't use gamma curve, we make encoding and >>> + * decoding explicit by defining an enum list of transfer functions supported >>> + * in terms of EOTF and inverse EOTF, where: >>> + * >>> + * - EOTF (electro-optical transfer function): is the transfer function to go >>> + * from the encoded value to an optical (linear) value. De-gamma functions >>> + * traditionally do this. >>> + * - Inverse EOTF (simply the inverse of the EOTF): is usually intended to go >>> + * from an optical/linear space (which might have been used for blending) >>> + * back to the encoded values. Gamma functions traditionally do this. >>> + */ >>> static const char * const >>> amdgpu_transfer_function_names[] = { >>> [AMDGPU_TRANSFER_FUNCTION_DEFAULT] = "Default", >> >> >
