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avutil: Extract gamma determination from PNG encoder for future use. Adds private avpriv_get_gamma_from_trc() function to libavutil.

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Signed-off-by: Kevin Wheatley <kevin.j.wheatley@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Kevin Wheatley 2015-03-05 10:37:51 +00:00 committed by Michael Niedermayer
parent 6db20926c3
commit 86b59e6a50
5 changed files with 97 additions and 26 deletions
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27
libavcodec/pngenc.c
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@ -28,6 +28,7 @@
#include "libavutil/avassert.h"
#include "libavutil/libm.h"
#include "libavutil/opt.h"
#include "libavutil/color_utils.h"
#include <zlib.h>
@ -277,31 +278,9 @@ static int png_get_chrm(enum AVColorPrimaries prim, uint8_t *buf)
static int png_get_gama(enum AVColorTransferCharacteristic trc, uint8_t *buf)
{
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:
double gamma = avpriv_get_gamma_from_trc(trc);
if (gamma <= 1e-6)
return 0;
}
AV_WB32_PNG(buf, 1.0 / gamma);
return 1;

1
libavutil/Makefile
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@ -88,6 +88,7 @@ OBJS = adler32.o \
cast5.o \
camellia.o \
channel_layout.o \
color_utils.o \
cpu.o \
crc.o \
des.o \

52
libavutil/color_utils.c Normal file
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@ -0,0 +1,52 @@
/*
* 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 "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;
}

39
libavutil/color_utils.h Normal file
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@ -0,0 +1,39 @@
/*
* 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);
#endif

2
libavutil/version.h
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@ -56,7 +56,7 @@
*/
#define LIBAVUTIL_VERSION_MAJOR 54
#define LIBAVUTIL_VERSION_MINOR 19
#define LIBAVUTIL_VERSION_MINOR 20
#define LIBAVUTIL_VERSION_MICRO 100
#define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \