From c63beb4581bcd3140e122b7a7c5b4a53ae35ec29 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomas=20H=C3=A4rdin?= <git@haerdin.se>
Date: Fri, 3 Feb 2023 14:00:38 +0100
Subject: [PATCH 2/2] lavfi/vf_colorspace: Add SMPTE ST 2084 support
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Also adds inits and onits options for specifying what 28672
means in terms of nits (cd/m²).
---
doc/filters.texi | 30 ++++++++++++++++++++++++++++
libavfilter/vf_colorspace.c | 39 +++++++++++++++++++++++++++++++++++--
2 files changed, 67 insertions(+), 2 deletions(-)
@@ -9839,6 +9839,10 @@ BT.2020 for 10-bits content
@item bt2020-12
BT.2020 for 12-bits content
+@anchor{smpte2084}
+@item smpte2084
+SMPTE ST 2084 (perceptual quantizer) used by BT.2100. See @ref{inits} and @ref{onits}.
+
@end table
@anchor{primaries}
@@ -9980,6 +9984,32 @@ Override input transfer characteristics. Same accepted values as @ref{trc}.
@item irange
Override input color range. Same accepted values as @ref{range}.
+@anchor{inits}
+@item inits
+Required when input trc is @ref{smpte2084}.
+Specifies what the peak intermediate level should correspond to in nits (cd/m²).
+Perceptually dequantized values get scaled and clipped so that the range [0,inits] fits in the filter's internal psuedo-restricted 15-bit format.
+For inits < 10000 this corresponds to clipping of values outside the [0,inits]³ RGB cube.
+For inits = 10000 values are not clipped, but values in the lower range will get truncated to zero due to the internal format's limited range.
+
+With BT.2100 input basic usage is:
+@example
+colorspace=bt709:inits=100
+@end example
+which clips HDR to SDR in BT.709 colorspace.
+
+A more advanced use case is as follows:
+@example
+colorspace=bt709:inits=10000:trc=linear:format=yuv444p16,tonemap=hable:peak=0.01
+@end example
+which with BT.2100 input performs very basic tonemapping.
+
+@anchor{onits}
+@item onits
+Used in combination with @ref{smpte2084}, defaults to 10000.
+Similar to @ref{inits} but in reverse.
+Specifies how to treat the peak intermediate level in nits (cd/m²) prior to perceptual quantization (PQ) as per SMPTE ST 2084.
+
@end table
The filter converts the transfer characteristics, color space and color
@@ -118,6 +118,7 @@ typedef struct ColorSpaceContext {
enum AVColorTransferCharacteristic in_trc, out_trc, user_trc, user_itrc;
enum AVColorPrimaries in_prm, out_prm, user_prm, user_iprm;
enum AVPixelFormat in_format, user_format;
+ double user_inits, user_onits;
int fast_mode;
enum DitherMode dither;
enum WhitepointAdaptation wp_adapt;
@@ -173,6 +174,7 @@ static const struct TransferCharacteristics transfer_characteristics[AVCOL_TRC_N
[AVCOL_TRC_IEC61966_2_4] = { 1.099, 0.018, 0.45, 4.5 },
[AVCOL_TRC_BT2020_10] = { 1.099, 0.018, 0.45, 4.5 },
[AVCOL_TRC_BT2020_12] = { 1.0993, 0.0181, 0.45, 4.5 },
+ [AVCOL_TRC_SMPTE2084] = { 1.0, 0, 0, 0 }, // fake entry, actual TRC uses entirely separate formula
};
static const struct TransferCharacteristics *
@@ -197,6 +199,9 @@ static int fill_gamma_table(ColorSpaceContext *s)
double in_ialpha = 1.0 / in_alpha, in_igamma = 1.0 / in_gamma, in_idelta = 1.0 / in_delta;
double out_alpha = s->out_txchr->alpha, out_beta = s->out_txchr->beta;
double out_gamma = s->out_txchr->gamma, out_delta = s->out_txchr->delta;
+ double m1 = 1305.0/8192, m2 = 2523.0/32, c2 = 2413.0/128, c3 = 2392.0/128, c1 = c3 - c2 + 1;
+ double im1 = 1.0 / m1, im2 = 1.0 / m2;
+ double iscale = 10000.0 / s->user_inits, ioscale = s->user_onits / 10000.0;
s->lin_lut = av_malloc(sizeof(*s->lin_lut) * 32768 * 2);
if (!s->lin_lut)
@@ -206,7 +211,15 @@ static int fill_gamma_table(ColorSpaceContext *s)
double v = (n - 2048.0) / 28672.0, d, l;
// delinearize
- if (v <= -out_beta) {
+ if (s->out_trc == AVCOL_TRC_SMPTE2084) {
+ // see BT.2100-2
+ if (v >= 0) {
+ double vm1 = pow(v * ioscale, m1);
+ d = pow((c1 + c2 * vm1)/(1 + c3 * vm1), m2);
+ } else {
+ d = 0;
+ }
+ } else if (v <= -out_beta) {
d = -out_alpha * pow(-v, out_gamma) + (out_alpha - 1.0);
} else if (v < out_beta) {
d = out_delta * v;
@@ -216,7 +229,19 @@ static int fill_gamma_table(ColorSpaceContext *s)
s->delin_lut[n] = av_clip_int16(lrint(d * 28672.0));
// linearize
- if (v <= -in_beta * in_delta) {
+ if (s->in_trc == AVCOL_TRC_SMPTE2084) {
+ // see BT.2100-2
+ if (v >= 0) {
+ double vim2 = pow(v, im2);
+ // for inits < 10000 this will tonemap by clipping in RGB
+ // for inits = 10000 this makes unclipped linear values accessible when trc=linear
+ // note that precision will be lost in the lower end of PQ values, for example with
+ // 12-bit PQ and 16-bit output the first 422 values all get truncated to zero
+ l = iscale * pow((vim2 - c1 > 0 ? vim2 - c1 : 0) / (c2 - c3 * vim2), im1);
+ } else {
+ l = 0;
+ }
+ } else if (v <= -in_beta * in_delta) {
l = -pow((1.0 - in_alpha - v) * in_ialpha, in_igamma);
} else if (v < in_beta * in_delta) {
l = v * in_idelta;
@@ -514,6 +539,11 @@ static int create_filtergraph(AVFilterContext *ctx,
}
}
+ if (s->in_trc == AVCOL_TRC_SMPTE2084 && s->user_inits <= 0) {
+ av_log(ctx, AV_LOG_ERROR, "smpte2084 requires inits\n");
+ return AVERROR(EINVAL);
+ }
+
if (!s->out_txchr) {
av_freep(&s->lin_lut);
s->out_trc = out->color_trc;
@@ -956,6 +986,7 @@ static const AVOption colorspace_options[] = {
ENUM("iec61966-2-4", AVCOL_TRC_IEC61966_2_4, "trc"),
ENUM("bt2020-10", AVCOL_TRC_BT2020_10, "trc"),
ENUM("bt2020-12", AVCOL_TRC_BT2020_12, "trc"),
+ ENUM("smpte2084", AVCOL_TRC_SMPTE2084, "trc"),
{ "format", "Output pixel format",
OFFSET(user_format), AV_OPT_TYPE_INT, { .i64 = AV_PIX_FMT_NONE },
@@ -1008,6 +1039,10 @@ static const AVOption colorspace_options[] = {
{ "itrc", "Input transfer characteristics",
OFFSET(user_itrc), AV_OPT_TYPE_INT, { .i64 = AVCOL_TRC_UNSPECIFIED },
AVCOL_TRC_RESERVED0, AVCOL_TRC_NB - 1, FLAGS, "trc" },
+ { "inits", "Input nits. Specifies how PQ (SMPTE ST 2084) values are to be mapped to intermediate/output linear RGB",
+ OFFSET(user_inits), AV_OPT_TYPE_DOUBLE, {.dbl = 0}, 0, 10000, FLAGS },
+ { "onits", "Output nits. Specifies how input/intermediate linear RGB is scaled for output PQ (SMPTE ST 2084) values",
+ OFFSET(user_onits), AV_OPT_TYPE_DOUBLE, {.dbl = 10000}, 1, 10000, FLAGS },
{ NULL }
};
--
2.30.2