From: Niklas Haas <g...@haasn.dev>
Logic ported from libplacebo's AVFrame helpers. The basic idea is to use the
provided MaxRGB/MaxSCL values to infer what the actual luminance would have
been, which HDR10+ metadata does not provide directly. It's worth pointing out
that this gives us an *upper* bound on the true maximum luminance, so any
error in the estimation cannot result in clipping.
---
libswscale/utils.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
diff --git a/libswscale/utils.c b/libswscale/utils.c
index 3d3fcadacc..b097ec51b2 100644
--- a/libswscale/utils.c
+++ b/libswscale/utils.c
@@ -43,6 +43,7 @@
#include "libavutil/cpu.h"
#include "libavutil/csp.h"
#include "libavutil/emms.h"
+#include "libavutil/hdr_dynamic_metadata.h"
#include "libavutil/imgutils.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/libm.h"
@@ -2745,6 +2746,55 @@ SwsFormat ff_fmt_from_frame(const AVFrame *frame, int
field)
}
}
+ if ((sd = av_frame_get_side_data(frame, AV_FRAME_DATA_DYNAMIC_HDR_PLUS))) {
+ const AVDynamicHDRPlus *dhp = (const AVDynamicHDRPlus *) sd->data;
+ const AVHDRPlusColorTransformParams *pars = &dhp->params[0];
+ const AVRational nits = av_make_q(10000, 1);
+ AVRational maxrgb = pars->maxscl[0];
+
+ if (!dhp->num_windows || dhp->application_version > 1)
+ goto skip_hdr10;
+
+ /* Maximum of MaxSCL components */
+ if (av_cmp_q(pars->maxscl[1], maxrgb) > 0)
+ maxrgb = pars->maxscl[1];
+ if (av_cmp_q(pars->maxscl[2], maxrgb) > 0)
+ maxrgb = pars->maxscl[2];
+
+ if (maxrgb.num > 0) {
+ /* Estimate true luminance from MaxSCL */
+ const AVLumaCoefficients *luma =
av_csp_luma_coeffs_from_avcsp(fmt.csp);
+ if (!luma)
+ goto skip_hdr10;
+ fmt.color.frame_peak = av_add_q(av_mul_q(luma->cr,
pars->maxscl[0]),
+ av_add_q(av_mul_q(luma->cg,
pars->maxscl[1]),
+ av_mul_q(luma->cb,
pars->maxscl[2])));
+ /* Scale the scene average brightness by the ratio between the
+ * maximum luminance and the MaxRGB values */
+ fmt.color.frame_avg = av_mul_q(pars->average_maxrgb,
+ av_div_q(fmt.color.frame_peak,
maxrgb));
+ } else {
+ /**
+ * Calculate largest value from histogram to use as fallback for
+ * clips with missing MaxSCL information. Note that this may end
+ * up picking the "reserved" value at the 5% percentile, which in
+ * practice appears to track the brightest pixel in the scene.
+ */
+ for (int i = 0; i < pars->num_distribution_maxrgb_percentiles;
i++) {
+ const AVRational pct = pars->distribution_maxrgb[i].percentile;
+ if (av_cmp_q(pct, maxrgb) > 0)
+ maxrgb = pct;
+ fmt.color.frame_peak = maxrgb;
+ fmt.color.frame_avg = pars->average_maxrgb;
+ }
+ }
+
+ /* Rescale to nits */
+ fmt.color.frame_peak = av_mul_q(nits, fmt.color.frame_peak);
+ fmt.color.frame_avg = av_mul_q(nits, fmt.color.frame_avg);
+ }
+skip_hdr10:
+
/* PQ is always scaled down to absolute zero, so ignore mastering metadata
*/
if (fmt.color.trc == AVCOL_TRC_SMPTE2084)
fmt.color.min_luma = av_make_q(0, 1);
--
2.47.0
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
