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[obs] hdr: use BT.2020 gamut for PQ decoding

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Mastering display primaries do not define the pixel encoding gamut.
This commit is contained in:
Geoffrey McRae
2026-07-17 18:35:05 +10:00
parent 2006fb640f
commit af47e7c1e9
1 changed files with 11 additions and 18 deletions
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29
obs/lg.c
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@@ -677,10 +677,6 @@ static DMAFrameInfo * dmabufOpenDMAFrameInfo(LGPlugin * this, LGMPMessage * msg,
}
#endif
/* chromaticity coordinates are transported in SMPTE ST 2086 units of
* 0.00002 */
#define LG_ST2086_UNIT 0.00002
static bool mat3Inverse(const double m[9], double out[9])
{
const double det =
@@ -748,10 +744,10 @@ static bool primariesToXYZ(double xr, double yr, double xg, double yg,
return true;
}
/* compute the linear-light matrix that converts the frame's source display
* primaries to BT.709. Falls back to identity (assume BT.709) if the metadata
* is missing or degenerate. */
static void lgComputeColorMatrix(LGPlugin * this, const KVMFRFrame * frame)
/* Compute the linear-light matrix that converts BT.2020 to BT.709. HDR10
* mastering-display primaries describe the display used to master the
* content; they do not change the BT.2020 encoding gamut of the pixels. */
static void lgComputeColorMatrix(LGPlugin * this)
{
static const double bt709[9] =
{
@@ -762,14 +758,11 @@ static void lgComputeColorMatrix(LGPlugin * this, const KVMFRFrame * frame)
const double * result = bt709;
double src[9], dst709[9], dst709inv[9], conv[9];
const double xr = frame->hdrDisplayPrimary[0][0] * LG_ST2086_UNIT;
const double yr = frame->hdrDisplayPrimary[0][1] * LG_ST2086_UNIT;
const double xg = frame->hdrDisplayPrimary[1][0] * LG_ST2086_UNIT;
const double yg = frame->hdrDisplayPrimary[1][1] * LG_ST2086_UNIT;
const double xb = frame->hdrDisplayPrimary[2][0] * LG_ST2086_UNIT;
const double yb = frame->hdrDisplayPrimary[2][1] * LG_ST2086_UNIT;
const double xw = frame->hdrWhitePoint[0] * LG_ST2086_UNIT;
const double yw = frame->hdrWhitePoint[1] * LG_ST2086_UNIT;
/* BT.2020 / D65 source */
const double xr = 0.7080, yr = 0.2920;
const double xg = 0.1700, yg = 0.7970;
const double xb = 0.1310, yb = 0.0460;
const double xw = 0.3127, yw = 0.3290;
/* BT.709 / D65 target */
if (primariesToXYZ(xr, yr, xg, yg, xb, yb, xw, yw, src) &&
@@ -781,7 +774,7 @@ static void lgComputeColorMatrix(LGPlugin * this, const KVMFRFrame * frame)
result = conv;
}
else
printf("HDR metadata missing or invalid, assuming BT.709 primaries\n");
printf("Failed to compute BT.2020 to BT.709 color matrix\n");
for (int r = 0; r < 3; ++r)
vec3_set(&this->colorMatrix[r],
@@ -831,7 +824,7 @@ static void lgFormatInit(LGPlugin * this, const KVMFRFrame * frame,
(float)frame->sdrWhiteLevel : (float)KVMFR_SDR_WHITE_LEVEL_DEFAULT;
if (this->hdr && this->hdrPQ)
lgComputeColorMatrix(this, frame);
lgComputeColorMatrix(this);
this->bpp = 4;
switch(this->type)