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

Signed-off-by: Kevin Wheatley <kevin.j.wheatley@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 52 insertions, 0 deletions

diff --git a/libavutil/color_utils.c b/libavutil/color_utils.c
new file mode 100644
index 0000000000..59146be8c2
--- /dev/null
+++ b/libavutil/color_utils.c
@@ -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;
+}