Following on from my previous email, this adds some functions to
actually convert from linear to non-linear encoding. I have another
that changes the OpenEXR codec to actually use these.
Kevin
From 59299c23489fadeb11330b51f83b152194f0810e Mon Sep 17 00:00:00 2001
From: Kevin Wheatley <kevin.j.wheat...@gmail.com>
Date: Tue, 1 Sep 2015 11:41:38 +0100
Subject: [PATCH 4/5] Add basic transfer functions for each AVColorTransferCharacteristic
Most functions are valid over a domain and range of [0.0-1.0] but
some are defined over greater. This patch does not deal with
AVColorRange and assumes AVCOL_RANGE_JPEG for the returned values.
Signed-off-by: Kevin Wheatley <kevin.j.wheat...@gmail.com>
---
libavutil/color_utils.c | 166 +++++++++++++++++++++++++++++++++++++++++++++++
libavutil/color_utils.h | 17 +++++
2 files changed, 183 insertions(+), 0 deletions(-)
diff --git a/libavutil/color_utils.c b/libavutil/color_utils.c
index 59146be..f84b5f5 100644
--- a/libavutil/color_utils.c
+++ b/libavutil/color_utils.c
@@ -18,6 +18,9 @@
* 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"
@@ -50,3 +53,166 @@ double avpriv_get_gamma_from_trc(enum AVColorTransferCharacteristic trc)
}
return gamma;
}
+
+#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);
+}
+
+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 = _trc_bt709;
+ break;
+
+ case AVCOL_TRC_GAMMA22:
+ func = _trc_gamma22;
+ break;
+ case AVCOL_TRC_GAMMA28:
+ func = _trc_gamma28;
+ break;
+
+ case AVCOL_TRC_SMPTE240M:
+ func = _trc_smpte240M;
+ break;
+
+ case AVCOL_TRC_LINEAR:
+ func = _trc_linear;
+ break;
+
+ case AVCOL_TRC_LOG:
+ func = _trc_log;
+ break;
+
+ case AVCOL_TRC_LOG_SQRT:
+ func = _trc_log_sqrt;
+ break;
+
+ case AVCOL_TRC_IEC61966_2_4:
+ func = _trc_iec61966_2_4;
+ break;
+
+ case AVCOL_TRC_BT1361_ECG:
+ func = _trc_bt1361;
+ break;
+
+ case AVCOL_TRC_IEC61966_2_1:
+ func = _trc_iec61966_2_1;
+ break;
+
+ case AVCOL_TRC_SMPTEST2084:
+ func = _trc_smpte_st2084;
+ break;
+
+ case AVCOL_TRC_SMPTEST428_1:
+ func = _trc_smpte_st428_1;
+ 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
index 3600a72..9529006 100644
--- a/libavutil/color_utils.h
+++ b/libavutil/color_utils.h
@@ -36,4 +36,21 @@
*/
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
--
1.7.1
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