Re: [FFmpeg-devel] [PATCH v2] avutil/{color_utils, csp}: merge color_utils into csp and expose API

[Paul B Mahol <onemda@gmail.com>]

On 1/30/23, Zhao Zhili <quinkblack@foxmail.com> wrote:
>
>
>> -----Original Message-----
>> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Leo Izen
>> Sent: 2023年1月31日 0:50
>> To: ffmpeg-devel@ffmpeg.org
>> Cc: Leo Izen <leo.izen@gmail.com>
>> Subject: [FFmpeg-devel] [PATCH v2] avutil/{color_utils, csp}: merge
>> color_utils into csp and expose API
>>
>> libavutil/color_utils contains some avpriv_ symbols that map
>> enum AVTransferCharacteristic values to gamma-curve approximations and
>> to the actual transfer functions to invert them (i.e. -> linear).
>>
>> There's two issues with this:
>> (1) avpriv is evil and should be avoided whenever possible
>> (2) libavutil/csp.h exposes a public API for handling color that
>>     already handles primaries and matricies
>>
>> I don't see any reason this API has to be private, so this commit takes
>> the functionality from avutil/color_utils and merges it into avutil/csp
>> with an exposed av_ API rather than the previous avpriv_ API.
>>
>> Every reference to the previous API has been updated to point to the
>> new one. color_utils.h has been deleted as well. This should not break
>> any applications as it only contained avpriv_ symbols in the first
>> place, so nothing in that header could be referenced by other
>> applications.
>
> Isn't it break old libavcodec which linked to the new libavutil?

Yes it is, thats why according to Anton it can not be pushed as is.

>
>>
>> Signed-off-by: Leo Izen <leo.izen@gmail.com>
>> ---
>>  doc/APIchanges                |   4 +
>>  libavcodec/exr.c              |   8 +-
>>  libavcodec/fflcms2.c          |   1 -
>>  libavcodec/pngenc.c           |   3 +-
>>  libavformat/movenc.c          |   7 +-
>>  libavutil/Makefile            |   1 -
>>  libavutil/color_utils.c       | 234 ----------------------------------
>>  libavutil/color_utils.h       |  56 --------
>>  libavutil/csp.c               | 172 +++++++++++++++++++++++++
>>  libavutil/csp.h               |  39 ++++++
>>  libavutil/tests/color_utils.c |   4 +-
>>  11 files changed, 225 insertions(+), 304 deletions(-)
>>  delete mode 100644 libavutil/color_utils.c
>>  delete mode 100644 libavutil/color_utils.h
>>
>> diff --git a/doc/APIchanges b/doc/APIchanges
>> index bc52a07964..f28eb59ed3 100644
>> --- a/doc/APIchanges
>> +++ b/doc/APIchanges
>> @@ -14,6 +14,10 @@ libavutil:     2021-04-27
>>
>>  API changes, most recent first:
>>
>> +2023-01-30 - xxxxxxxxxx - lavu 57.44.100 - csp.h
>> +  Add av_csp_approximate_trc_gamma() and av_csp_trc_func_from_id().
>> +  Add av_csp_trc_function.
>> +
>>  2023-01-29 - xxxxxxxxxx - lavc 59.59.100 - avcodec.h
>>    Add AV_CODEC_FLAG_COPY_OPAQUE and AV_CODEC_FLAG_FRAME_DURATION.
>>
>> diff --git a/libavcodec/exr.c b/libavcodec/exr.c
>> index 6a0af96ce4..2f1766c17b 100644
>> --- a/libavcodec/exr.c
>> +++ b/libavcodec/exr.c
>> @@ -36,11 +36,11 @@
>>
>>  #include "libavutil/avassert.h"
>>  #include "libavutil/common.h"
>> +#include "libavutil/csp.h"
>>  #include "libavutil/imgutils.h"
>>  #include "libavutil/intfloat.h"
>>  #include "libavutil/avstring.h"
>>  #include "libavutil/opt.h"
>> -#include "libavutil/color_utils.h"
>>  #include "libavutil/half2float.h"
>>
>>  #include "avcodec.h"
>> @@ -1189,7 +1189,7 @@ static int decode_block(AVCodecContext *avctx, void
>> *tdata,
>>      int i, x, buf_size = s->buf_size;
>>      int c, rgb_channel_count;
>>      float one_gamma = 1.0f / s->gamma;
>> -    avpriv_trc_function trc_func =
>> avpriv_get_trc_function_from_trc(s->apply_trc_type);
>> +    av_csp_trc_function trc_func =
>> av_csp_trc_func_from_id(s->apply_trc_type);
>>      int ret;
>>
>>      line_offset = AV_RL64(s->gb.buffer + jobnr * 8);
>> @@ -2215,7 +2215,7 @@ static av_cold int decode_init(AVCodecContext
>> *avctx)
>>      uint32_t i;
>>      union av_intfloat32 t;
>>      float one_gamma = 1.0f / s->gamma;
>> -    avpriv_trc_function trc_func = NULL;
>> +    av_csp_trc_function trc_func = NULL;
>>
>>      ff_init_half2float_tables(&s->h2f_tables);
>>
>> @@ -2227,7 +2227,7 @@ static av_cold int decode_init(AVCodecContext
>> *avctx)
>>      ff_bswapdsp_init(&s->bbdsp);
>>  #endif
>>
>> -    trc_func = avpriv_get_trc_function_from_trc(s->apply_trc_type);
>> +    trc_func = av_csp_trc_func_from_id(s->apply_trc_type);
>>      if (trc_func) {
>>          for (i = 0; i < 65536; ++i) {
>>              t.i = half2float(i, &s->h2f_tables);
>> diff --git a/libavcodec/fflcms2.c b/libavcodec/fflcms2.c
>> index fd370fb310..5443f178bc 100644
>> --- a/libavcodec/fflcms2.c
>> +++ b/libavcodec/fflcms2.c
>> @@ -17,7 +17,6 @@
>>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>> 02110-1301 USA
>>   */
>>
>> -#include "libavutil/color_utils.h"
>>  #include "libavutil/csp.h"
>>
>>  #include "fflcms2.h"
>> diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
>> index 2393161c3b..ac27eebf3a 100644
>> --- a/libavcodec/pngenc.c
>> +++ b/libavcodec/pngenc.c
>> @@ -29,7 +29,6 @@
>>  #include "zlib_wrapper.h"
>>
>>  #include "libavutil/avassert.h"
>> -#include "libavutil/color_utils.h"
>>  #include "libavutil/crc.h"
>>  #include "libavutil/csp.h"
>>  #include "libavutil/libm.h"
>> @@ -317,7 +316,7 @@ static int png_get_chrm(enum AVColorPrimaries prim,
>> uint8_t *buf)
>>
>>  static int png_get_gama(enum AVColorTransferCharacteristic trc, uint8_t
>> *buf)
>>  {
>> -    double gamma = avpriv_get_gamma_from_trc(trc);
>> +    double gamma = av_csp_approximate_trc_gamma(trc);
>>      if (gamma <= 1e-6)
>>          return 0;
>>
>> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
>> index 8d31317838..6182dc7f58 100644
>> --- a/libavformat/movenc.c
>> +++ b/libavformat/movenc.c
>> @@ -47,6 +47,7 @@
>>  #include "internal.h"
>>  #include "libavutil/avstring.h"
>>  #include "libavutil/channel_layout.h"
>> +#include "libavutil/csp.h"
>>  #include "libavutil/intfloat.h"
>>  #include "libavutil/mathematics.h"
>>  #include "libavutil/libm.h"
>> @@ -56,7 +57,6 @@
>>  #include "libavutil/stereo3d.h"
>>  #include "libavutil/timecode.h"
>>  #include "libavutil/dovi_meta.h"
>> -#include "libavutil/color_utils.h"
>>  #include "libavutil/uuid.h"
>>  #include "hevc.h"
>>  #include "rtpenc.h"
>> @@ -2011,9 +2011,8 @@ static int mov_write_pasp_tag(AVIOContext *pb,
>> MOVTrack *track)
>>  static int mov_write_gama_tag(AVFormatContext *s, AVIOContext *pb,
>> MOVTrack *track, double gamma)
>>  {
>>      uint32_t gama = 0;
>> -    if (gamma <= 0.0) {
>> -        gamma = avpriv_get_gamma_from_trc(track->par->color_trc);
>> -    }
>> +    if (gamma <= 0.0)
>> +        gamma = av_csp_approximate_trc_gamma(track->par->color_trc);
>>      av_log(s, AV_LOG_DEBUG, "gamma value %g\n", gamma);
>>
>>      if (gamma > 1e-6) {
>> diff --git a/libavutil/Makefile b/libavutil/Makefile
>> index 29b06665f5..dc9012f9a8 100644
>> --- a/libavutil/Makefile
>> +++ b/libavutil/Makefile
>> @@ -114,7 +114,6 @@ OBJS = adler32.o
>>                  \
>>         cast5.o                                                          \
>>         camellia.o                                                       \
>>         channel_layout.o                                                 \
>> -       color_utils.o                                                    \
>>         cpu.o                                                            \
>>         crc.o                                                            \
>>         csp.o                                                            \
>> diff --git a/libavutil/color_utils.c b/libavutil/color_utils.c
>> deleted file mode 100644
>> index 5e221fb798..0000000000
>> --- a/libavutil/color_utils.c
>> +++ /dev/null
>> @@ -1,234 +0,0 @@
>> -/*
>> - * Copyright (c) 2015 Kevin Wheatley <kevin.j.wheatley@gmail.com>
>> - *
>> - * This file is part of FFmpeg.
>> - *
>> - * FFmpeg is free software; you can redistribute it and/or
>> - * modify it under the terms of the GNU Lesser General Public
>> - * License as published by the Free Software Foundation; either
>> - * version 2.1 of the License, or (at your option) any later version.
>> - *
>> - * FFmpeg is distributed in the hope that it will be useful,
>> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> - * Lesser General Public License for more details.
>> - *
>> - * You should have received a copy of the GNU Lesser General Public
>> - * License along with FFmpeg; if not, write to the Free Software
>> - * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>> 02110-1301 USA
>> - */
>> -
>> -#include <stddef.h>
>> -#include <math.h>
>> -
>> -#include "libavutil/color_utils.h"
>> -#include "libavutil/pixfmt.h"
>> -
>> -double avpriv_get_gamma_from_trc(enum AVColorTransferCharacteristic trc)
>> -{
>> -    double gamma;
>> -    switch (trc) {
>> -        case AVCOL_TRC_BT709:
>> -        case AVCOL_TRC_SMPTE170M:
>> -        case AVCOL_TRC_SMPTE240M:
>> -        case AVCOL_TRC_BT1361_ECG:
>> -        case AVCOL_TRC_BT2020_10:
>> -        case AVCOL_TRC_BT2020_12:
>> -            /* these share a segmented TRC, but gamma 1.961 is a close
>> -              approximation, and also more correct for decoding content
>> */
>> -            gamma = 1.961;
>> -            break;
>> -        case AVCOL_TRC_GAMMA22:
>> -        case AVCOL_TRC_IEC61966_2_1:
>> -            gamma = 2.2;
>> -            break;
>> -        case AVCOL_TRC_GAMMA28:
>> -            gamma = 2.8;
>> -            break;
>> -        case AVCOL_TRC_LINEAR:
>> -            gamma = 1.0;
>> -            break;
>> -        default:
>> -            gamma = 0.0; // Unknown value representation
>> -    }
>> -    return gamma;
>> -}
>> -
>> -#define BT709_alpha 1.099296826809442
>> -#define BT709_beta 0.018053968510807
>> -
>> -static double avpriv_trc_bt709(double Lc)
>> -{
>> -    const double a = BT709_alpha;
>> -    const double b = BT709_beta;
>> -
>> -    return (0.0 > Lc) ? 0.0
>> -         : (  b > Lc) ? 4.500 * Lc
>> -         :              a * pow(Lc, 0.45) - (a - 1.0);
>> -}
>> -
>> -static double avpriv_trc_gamma22(double Lc)
>> -{
>> -    return (0.0 > Lc) ? 0.0 : pow(Lc, 1.0/ 2.2);
>> -}
>> -
>> -static double avpriv_trc_gamma28(double Lc)
>> -{
>> -    return (0.0 > Lc) ? 0.0 : pow(Lc, 1.0/ 2.8);
>> -}
>> -
>> -static double avpriv_trc_smpte240M(double Lc)
>> -{
>> -    const double a = 1.1115;
>> -    const double b = 0.0228;
>> -
>> -    return (0.0 > Lc) ? 0.0
>> -         : (  b > Lc) ? 4.000 * Lc
>> -         :              a * pow(Lc, 0.45) - (a - 1.0);
>> -}
>> -
>> -static double avpriv_trc_linear(double Lc)
>> -{
>> -    return Lc;
>> -}
>> -
>> -static double avpriv_trc_log(double Lc)
>> -{
>> -    return (0.01 > Lc) ? 0.0 : 1.0 + log10(Lc) / 2.0;
>> -}
>> -
>> -static double avpriv_trc_log_sqrt(double Lc)
>> -{
>> -    // sqrt(10) / 1000
>> -    return (0.00316227766 > Lc) ? 0.0 : 1.0 + log10(Lc) / 2.5;
>> -}
>> -
>> -static double avpriv_trc_iec61966_2_4(double Lc)
>> -{
>> -    const double a = BT709_alpha;
>> -    const double b = BT709_beta;
>> -
>> -    return (-b >= Lc) ? -a * pow(-Lc, 0.45) + (a - 1.0)
>> -         : ( b >  Lc) ? 4.500 * Lc
>> -         :               a * pow( Lc, 0.45) - (a - 1.0);
>> -}
>> -
>> -static double avpriv_trc_bt1361(double Lc)
>> -{
>> -    const double a = BT709_alpha;
>> -    const double b = BT709_beta;
>> -
>> -    return (-0.0045 >= Lc) ? -(a * pow(-4.0 * Lc, 0.45) + (a - 1.0)) /
>> 4.0
>> -         : ( b >  Lc) ? 4.500 * Lc
>> -         :               a * pow( Lc, 0.45) - (a - 1.0);
>> -}
>> -
>> -static double avpriv_trc_iec61966_2_1(double Lc)
>> -{
>> -    const double a = 1.055;
>> -    const double b = 0.0031308;
>> -
>> -    return (0.0 > Lc) ? 0.0
>> -         : (  b > Lc) ? 12.92 * Lc
>> -         :              a * pow(Lc, 1.0  / 2.4) - (a - 1.0);
>> -}
>> -
>> -static double avpriv_trc_smpte_st2084(double Lc)
>> -{
>> -    const double c1 =         3424.0 / 4096.0; // c3-c2 + 1
>> -    const double c2 =  32.0 * 2413.0 / 4096.0;
>> -    const double c3 =  32.0 * 2392.0 / 4096.0;
>> -    const double m  = 128.0 * 2523.0 / 4096.0;
>> -    const double n  =  0.25 * 2610.0 / 4096.0;
>> -    const double L  = Lc / 10000.0;
>> -    const double Ln = pow(L, n);
>> -
>> -    return (0.0 > Lc) ? 0.0
>> -         :              pow((c1 + c2 * Ln) / (1.0 + c3 * Ln), m);
>> -
>> -}
>> -
>> -static double avpriv_trc_smpte_st428_1(double Lc)
>> -{
>> -    return (0.0 > Lc) ? 0.0
>> -         :              pow(48.0 * Lc / 52.37, 1.0 / 2.6);
>> -}
>> -
>> -
>> -static double avpriv_trc_arib_std_b67(double Lc) {
>> -    // The function uses the definition from HEVC, which assumes that the
>> peak
>> -    // white is input level = 1. (this is equivalent to scaling E = Lc *
>> 12 and
>> -    // using the definition from the ARIB STD-B67 spec)
>> -    const double a = 0.17883277;
>> -    const double b = 0.28466892;
>> -    const double c = 0.55991073;
>> -    return (0.0 > Lc) ? 0.0 :
>> -        (Lc <= 1.0 / 12.0 ? sqrt(3.0 * Lc) : a * log(12.0 * Lc - b) + c);
>> -}
>> -
>> -avpriv_trc_function avpriv_get_trc_function_from_trc(enum
>> AVColorTransferCharacteristic trc)
>> -{
>> -    avpriv_trc_function func = NULL;
>> -    switch (trc) {
>> -        case AVCOL_TRC_BT709:
>> -        case AVCOL_TRC_SMPTE170M:
>> -        case AVCOL_TRC_BT2020_10:
>> -        case AVCOL_TRC_BT2020_12:
>> -            func = avpriv_trc_bt709;
>> -            break;
>> -
>> -        case AVCOL_TRC_GAMMA22:
>> -            func = avpriv_trc_gamma22;
>> -            break;
>> -        case AVCOL_TRC_GAMMA28:
>> -            func = avpriv_trc_gamma28;
>> -            break;
>> -
>> -        case AVCOL_TRC_SMPTE240M:
>> -            func = avpriv_trc_smpte240M;
>> -            break;
>> -
>> -        case AVCOL_TRC_LINEAR:
>> -            func = avpriv_trc_linear;
>> -            break;
>> -
>> -        case AVCOL_TRC_LOG:
>> -            func = avpriv_trc_log;
>> -            break;
>> -
>> -        case AVCOL_TRC_LOG_SQRT:
>> -            func = avpriv_trc_log_sqrt;
>> -            break;
>> -
>> -        case AVCOL_TRC_IEC61966_2_4:
>> -            func = avpriv_trc_iec61966_2_4;
>> -            break;
>> -
>> -        case AVCOL_TRC_BT1361_ECG:
>> -            func = avpriv_trc_bt1361;
>> -            break;
>> -
>> -        case AVCOL_TRC_IEC61966_2_1:
>> -            func = avpriv_trc_iec61966_2_1;
>> -            break;
>> -
>> -        case AVCOL_TRC_SMPTEST2084:
>> -            func = avpriv_trc_smpte_st2084;
>> -            break;
>> -
>> -        case AVCOL_TRC_SMPTEST428_1:
>> -            func = avpriv_trc_smpte_st428_1;
>> -            break;
>> -
>> -        case AVCOL_TRC_ARIB_STD_B67:
>> -            func = avpriv_trc_arib_std_b67;
>> -            break;
>> -
>> -        case AVCOL_TRC_RESERVED0:
>> -        case AVCOL_TRC_UNSPECIFIED:
>> -        case AVCOL_TRC_RESERVED:
>> -        default:
>> -            break;
>> -    }
>> -    return func;
>> -}
>> diff --git a/libavutil/color_utils.h b/libavutil/color_utils.h
>> deleted file mode 100644
>> index 9529006452..0000000000
>> --- a/libavutil/color_utils.h
>> +++ /dev/null
>> @@ -1,56 +0,0 @@
>> -/*
>> - * Copyright (c) 2015 Kevin Wheatley <kevin.j.wheatley@gmail.com>
>> - *
>> - * This file is part of FFmpeg.
>> - *
>> - * FFmpeg is free software; you can redistribute it and/or
>> - * modify it under the terms of the GNU Lesser General Public
>> - * License as published by the Free Software Foundation; either
>> - * version 2.1 of the License, or (at your option) any later version.
>> - *
>> - * FFmpeg is distributed in the hope that it will be useful,
>> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> - * Lesser General Public License for more details.
>> - *
>> - * You should have received a copy of the GNU Lesser General Public
>> - * License along with FFmpeg; if not, write to the Free Software
>> - * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>> 02110-1301 USA
>> - */
>> -
>> -#ifndef AVUTIL_COLOR_UTILS_H
>> -#define AVUTIL_COLOR_UTILS_H
>> -
>> -
>> -#include "libavutil/pixfmt.h"
>> -
>> -/**
>> - * Determine a suitable 'gamma' value to match the supplied
>> - * AVColorTransferCharacteristic.
>> - *
>> - * See Apple Technical Note TN2257
>> (https://developer.apple.com/library/mac/technotes/tn2257/_index.html)
>> - *
>> - * @return Will return an approximation to the simple gamma function
>> matching
>> - *         the supplied Transfer Characteristic, Will return 0.0 for any
>> - *         we cannot reasonably match against.
>> - */
>> -double avpriv_get_gamma_from_trc(enum AVColorTransferCharacteristic trc);
>> -
>> -
>> -typedef double (*avpriv_trc_function)(double);
>> -
>> -/**
>> - * Determine the function needed to apply the given
>> - * AVColorTransferCharacteristic to linear input.
>> - *
>> - * The function returned should expect a nominal domain and range of
>> [0.0-1.0]
>> - * values outside of this range maybe valid depending on the chosen
>> - * characteristic function.
>> - *
>> - * @return Will return pointer to the function matching the
>> - *         supplied Transfer Characteristic. If unspecified will
>> - *         return NULL:
>> - */
>> -avpriv_trc_function avpriv_get_trc_function_from_trc(enum
>> AVColorTransferCharacteristic trc);
>> -
>> -#endif
>> diff --git a/libavutil/csp.c b/libavutil/csp.c
>> index 98fc83c1da..7ef822c60b 100644
>> --- a/libavutil/csp.c
>> +++ b/libavutil/csp.c
>> @@ -1,5 +1,8 @@
>>  /*
>> + * Copyright (c) 2015 Kevin Wheatley <kevin.j.wheatley@gmail.com>
>>   * Copyright (c) 2016 Ronald S. Bultje <rsbultje@gmail.com>
>> + * Copyright (c) 2023 Leo Izen <leo.izen@gmail.com>
>> + *
>>   * This file is part of FFmpeg.
>>   *
>>   * FFmpeg is free software; you can redistribute it and/or
>> @@ -21,9 +24,11 @@
>>   * @file Colorspace functions for libavutil
>>   * @author Ronald S. Bultje <rsbultje@gmail.com>
>>   * @author Leo Izen <leo.izen@gmail.com>
>> + * @author Kevin Wheatley <kevin.j.wheatley@gmail.com>
>>   */
>>
>>  #include <stdlib.h>
>> +#include <math.h>
>>
>>  #include "attributes.h"
>>  #include "csp.h"
>> @@ -126,3 +131,170 @@ enum AVColorPrimaries
>> av_csp_primaries_id_from_desc(const AVColorPrimariesDesc *
>>
>>      return AVCOL_PRI_UNSPECIFIED;
>>  }
>> +
>> +static const double approximate_gamma[AVCOL_TRC_NB] = {
>> +    [AVCOL_TRC_BT709] = 1.961,
>> +    [AVCOL_TRC_SMPTE170M] = 1.961,
>> +    [AVCOL_TRC_SMPTE240M] = 1.961,
>> +    [AVCOL_TRC_BT1361_ECG] = 1.961,
>> +    [AVCOL_TRC_BT2020_10] = 1.961,
>> +    [AVCOL_TRC_BT2020_12] = 1.961,
>> +    [AVCOL_TRC_GAMMA22] = 2.2,
>> +    [AVCOL_TRC_IEC61966_2_1] = 2.2,
>> +    [AVCOL_TRC_GAMMA28] = 2.8,
>> +    [AVCOL_TRC_LINEAR] = 1.0,
>> +    [AVCOL_TRC_SMPTE428] = 2.6,
>> +};
>> +
>> +double av_csp_approximate_trc_gamma(enum AVColorTransferCharacteristic
>> trc)
>> +{
>> +    double gamma;
>> +    if (trc >= AVCOL_TRC_NB)
>> +        return 0.0;
>> +    gamma = approximate_gamma[trc];
>> +    if (gamma > 0)
>> +        return gamma;
>> +    return 0.0;
>> +}
>> +
>> +#define BT709_alpha 1.099296826809442
>> +#define BT709_beta 0.018053968510807
>> +
>> +static double trc_bt709(double Lc)
>> +{
>> +    const double a = BT709_alpha;
>> +    const double b = BT709_beta;
>> +
>> +    return (0.0 > Lc) ? 0.0
>> +         : (  b > Lc) ? 4.500 * Lc
>> +         :              a * pow(Lc, 0.45) - (a - 1.0);
>> +}
>> +
>> +static double trc_gamma22(double Lc)
>> +{
>> +    return (0.0 > Lc) ? 0.0 : pow(Lc, 1.0/ 2.2);
>> +}
>> +
>> +static double trc_gamma28(double Lc)
>> +{
>> +    return (0.0 > Lc) ? 0.0 : pow(Lc, 1.0/ 2.8);
>> +}
>> +
>> +static double trc_smpte240M(double Lc)
>> +{
>> +    const double a = 1.1115;
>> +    const double b = 0.0228;
>> +
>> +    return (0.0 > Lc) ? 0.0
>> +         : (  b > Lc) ? 4.000 * Lc
>> +         :              a * pow(Lc, 0.45) - (a - 1.0);
>> +}
>> +
>> +static double trc_linear(double Lc)
>> +{
>> +    return Lc;
>> +}
>> +
>> +static double trc_log(double Lc)
>> +{
>> +    return (0.01 > Lc) ? 0.0 : 1.0 + log10(Lc) / 2.0;
>> +}
>> +
>> +static double trc_log_sqrt(double Lc)
>> +{
>> +    // sqrt(10) / 1000
>> +    return (0.00316227766 > Lc) ? 0.0 : 1.0 + log10(Lc) / 2.5;
>> +}
>> +
>> +static double trc_iec61966_2_4(double Lc)
>> +{
>> +    const double a = BT709_alpha;
>> +    const double b = BT709_beta;
>> +
>> +    return (-b >= Lc) ? -a * pow(-Lc, 0.45) + (a - 1.0)
>> +         : ( b >  Lc) ? 4.500 * Lc
>> +         :               a * pow( Lc, 0.45) - (a - 1.0);
>> +}
>> +
>> +static double trc_bt1361(double Lc)
>> +{
>> +    const double a = BT709_alpha;
>> +    const double b = BT709_beta;
>> +
>> +    return (-0.0045 >= Lc) ? -(a * pow(-4.0 * Lc, 0.45) + (a - 1.0)) /
>> 4.0
>> +         : ( b >  Lc) ? 4.500 * Lc
>> +         :               a * pow( Lc, 0.45) - (a - 1.0);
>> +}
>> +
>> +static double trc_iec61966_2_1(double Lc)
>> +{
>> +    const double a = 1.055;
>> +    const double b = 0.0031308;
>> +
>> +    return (0.0 > Lc) ? 0.0
>> +         : (  b > Lc) ? 12.92 * Lc
>> +         :              a * pow(Lc, 1.0  / 2.4) - (a - 1.0);
>> +}
>> +
>> +static double trc_smpte_st2084(double Lc)
>> +{
>> +    const double c1 =         3424.0 / 4096.0; // c3-c2 + 1
>> +    const double c2 =  32.0 * 2413.0 / 4096.0;
>> +    const double c3 =  32.0 * 2392.0 / 4096.0;
>> +    const double m  = 128.0 * 2523.0 / 4096.0;
>> +    const double n  =  0.25 * 2610.0 / 4096.0;
>> +    const double L  = Lc / 10000.0;
>> +    const double Ln = pow(L, n);
>> +
>> +    return (0.0 > Lc) ? 0.0
>> +         :              pow((c1 + c2 * Ln) / (1.0 + c3 * Ln), m);
>> +
>> +}
>> +
>> +static double trc_smpte_st428_1(double Lc)
>> +{
>> +    return (0.0 > Lc) ? 0.0
>> +         :              pow(48.0 * Lc / 52.37, 1.0 / 2.6);
>> +}
>> +
>> +
>> +static double trc_arib_std_b67(double Lc) {
>> +    // The function uses the definition from HEVC, which assumes that the
>> peak
>> +    // white is input level = 1. (this is equivalent to scaling E = Lc *
>> 12 and
>> +    // using the definition from the ARIB STD-B67 spec)
>> +    const double a = 0.17883277;
>> +    const double b = 0.28466892;
>> +    const double c = 0.55991073;
>> +    return (0.0 > Lc) ? 0.0 :
>> +        (Lc <= 1.0 / 12.0 ? sqrt(3.0 * Lc) : a * log(12.0 * Lc - b) + c);
>> +}
>> +
>> +static const av_csp_trc_function trc_funcs[AVCOL_TRC_NB] = {
>> +    [AVCOL_TRC_BT709] = trc_bt709,
>> +    [AVCOL_TRC_GAMMA22] = trc_gamma22,
>> +    [AVCOL_TRC_GAMMA28] = trc_gamma28,
>> +    [AVCOL_TRC_SMPTE170M] = trc_bt709,
>> +    [AVCOL_TRC_SMPTE240M] = trc_smpte240M,
>> +    [AVCOL_TRC_LINEAR] = trc_linear,
>> +    [AVCOL_TRC_LOG] = trc_log,
>> +    [AVCOL_TRC_LOG_SQRT] = trc_log_sqrt,
>> +    [AVCOL_TRC_IEC61966_2_4] = trc_iec61966_2_4,
>> +    [AVCOL_TRC_BT1361_ECG] = trc_bt1361,
>> +    [AVCOL_TRC_IEC61966_2_1] = trc_iec61966_2_1,
>> +    [AVCOL_TRC_BT2020_10] = trc_bt709,
>> +    [AVCOL_TRC_BT2020_12] = trc_bt709,
>> +    [AVCOL_TRC_SMPTE2084] = trc_smpte_st2084,
>> +    [AVCOL_TRC_SMPTE428] = trc_smpte_st428_1,
>> +    [AVCOL_TRC_ARIB_STD_B67] = trc_arib_std_b67,
>> +};
>> +
>> +av_csp_trc_function av_csp_trc_func_from_id(enum
>> AVColorTransferCharacteristic trc)
>> +{
>> +    av_csp_trc_function func;
>> +    if (trc >= AVCOL_TRC_NB)
>> +        return NULL;
>> +    func = trc_funcs[trc];
>> +    if (!func)
>> +        return NULL;
>> +    return func;
>> +}
>> diff --git a/libavutil/csp.h b/libavutil/csp.h
>> index 18ef208adf..73bce52bc0 100644
>> --- a/libavutil/csp.h
>> +++ b/libavutil/csp.h
>> @@ -1,5 +1,8 @@
>>  /*
>> + * Copyright (c) 2015 Kevin Wheatley <kevin.j.wheatley@gmail.com>
>>   * Copyright (c) 2016 Ronald S. Bultje <rsbultje@gmail.com>
>> + * Copyright (c) 2023 Leo Izen <leo.izen@gmail.com>
>> + *
>>   * This file is part of FFmpeg.
>>   *
>>   * FFmpeg is free software; you can redistribute it and/or
>> @@ -29,6 +32,7 @@
>>   * @ingroup lavu_math_csp
>>   * @author Ronald S. Bultje <rsbultje@gmail.com>
>>   * @author Leo Izen <leo.izen@gmail.com>
>> + * @author Kevin Wheatley <kevin.j.wheatley@gmail.com>
>>   */
>>
>>  /**
>> @@ -76,6 +80,12 @@ typedef struct AVColorPrimariesDesc {
>>      AVPrimaryCoefficients prim;
>>  } AVColorPrimariesDesc;
>>
>> +/**
>> + * Function pointer representing a double -> double transfer function
>> that performs
>> + * an EOTF transfer inversion. This function outputs linear light.
>> + */
>> +typedef double (*av_csp_trc_function)(double);
>> +
>>  /**
>>   * Retrieves the Luma coefficients necessary to construct a conversion
>> matrix
>>   * from an enum constant describing the colorspace.
>> @@ -104,6 +114,35 @@ const AVColorPrimariesDesc
>> *av_csp_primaries_desc_from_id(enum AVColorPrimaries
>>   */
>>  enum AVColorPrimaries av_csp_primaries_id_from_desc(const
>> AVColorPrimariesDesc *prm);
>>
>> +/**
>> + * Determine a suitable 'gamma' value to match the supplied
>> + * AVColorTransferCharacteristic.
>> + *
>> + * See Apple Technical Note TN2257
>> (https://developer.apple.com/library/mac/technotes/tn2257/_index.html)
>> + *
>> + * This function returns the gamma exponent for the OETF. For example,
>> sRGB is approximated
>> + * by gamma 2.2, not by gamma 0.45455.
>> + *
>> + * @return Will return an approximation to the simple gamma function
>> matching
>> + *         the supplied Transfer Characteristic, Will return 0.0 for any
>> + *         we cannot reasonably match against.
>> + */
>> +double av_csp_approximate_trc_gamma(enum AVColorTransferCharacteristic
>> trc);
>> +
>> +/**
>> + * Determine the function needed to apply the given
>> + * AVColorTransferCharacteristic to linear input.
>> + *
>> + * The function returned should expect a nominal domain and range of
>> [0.0-1.0]
>> + * values outside of this range maybe valid depending on the chosen
>> + * characteristic function.
>> + *
>> + * @return Will return pointer to the function matching the
>> + *         supplied Transfer Characteristic. If unspecified will
>> + *         return NULL:
>> + */
>> +av_csp_trc_function av_csp_trc_func_from_id(enum
>> AVColorTransferCharacteristic trc);
>> +
>>  /**
>>   * @}
>>   */
>> diff --git a/libavutil/tests/color_utils.c b/libavutil/tests/color_utils.c
>> index 4bdc550330..95fb3c1d56 100644
>> --- a/libavutil/tests/color_utils.c
>> +++ b/libavutil/tests/color_utils.c
>> @@ -19,7 +19,7 @@
>>   */
>>
>>  #include <stdio.h>
>> -#include "libavutil/color_utils.c"
>> +#include "libavutil/csp.h"
>>  #include "libavutil/macros.h"
>>
>>  int main(int argc, char *argv[])
>> @@ -32,7 +32,7 @@ int main(int argc, char *argv[])
>>    };
>>
>>    for(i = 0; i < AVCOL_TRC_NB; i++) {
>> -      avpriv_trc_function func = avpriv_get_trc_function_from_trc(i);
>> +      av_csp_trc_function func = av_csp_trc_func_from_id(i);
>>        for(j = 0; j < FF_ARRAY_ELEMS(test_data); j++) {
>>            if(func != NULL) {
>>                double result = func(test_data[j]);
>> --
>> 2.39.1
>>
>> _______________________________________________
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>> ffmpeg-devel@ffmpeg.org
>> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>
>> To unsubscribe, visit link above, or email
>> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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