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

["Zhao Zhili" <quinkblack@foxmail.com>]

> -----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?

> 
> 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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> 
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