avutil/color_utils: 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.wheatley@gmail.com>

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 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);
+}
+
+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_RESERVED0:
+        case AVCOL_TRC_UNSPECIFIED:
+        case AVCOL_TRC_RESERVED:
+        default:
+            break;
+    }
+    return func;
+}

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