video-color: add gamma encode/decode functions

Add functions to encode and decode gamma.
Add unit test to check that encode and decode are eachothers inverse
and that the limits are respected.

gst-libs/gst/video/video-color.c

@@ -25,6 +25,7 @@
 
 #include <string.h>
 #include <stdio.h>
+#include <math.h>
 
 #include "video-color.h"
 
@@ -314,3 +315,160 @@ gst_video_color_matrix_get_Kr_Kb (GstVideoColorMatrix matrix, gdouble * Kr,
 
   return res;
 }
+
+/**
+ * gst_video_color_transfer_encode:
+ * @func: a #GstVideoTransferFunction
+ * @val: a value
+ *
+ * Convert @val to its gamma encoded value.
+ *
+ * For a linear value L in the range [0..1], conversion to the non-linear
+ * (gamma encoded) L' is in general performed with a power function like:
+ *
+ * |[
+ *    L' = L ^ (1 / gamma)
+ * ]|
+ *
+ * Depending on @func, different formulas might be applied. Some formulas
+ * encode a linear segment in the lower range.
+ *
+ * Returns: the gamme encoded value of @val
+ *
+ * Since: 1.6
+ */
+gdouble
+gst_video_color_transfer_encode (GstVideoTransferFunction func, gdouble val)
+{
+  gdouble res;
+
+  switch (func) {
+    case GST_VIDEO_TRANSFER_UNKNOWN:
+    case GST_VIDEO_TRANSFER_GAMMA10:
+    default:
+      res = val;
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA18:
+      res = pow (val, 1.0 / 1.8);
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA20:
+      res = pow (val, 1.0 / 2.0);
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA22:
+      res = pow (val, 1.0 / 2.2);
+      break;
+    case GST_VIDEO_TRANSFER_BT709:
+      if (val < 0.018)
+        res = 4.5 * val;
+      else
+        res = 1.099 * pow (val, 0.45) - 0.099;
+      break;
+    case GST_VIDEO_TRANSFER_SMPTE240M:
+      if (val < 0.0228)
+        res = val * 4.0;
+      else
+        res = 1.1115 * pow (val, 0.45) - 0.1115;
+      break;
+    case GST_VIDEO_TRANSFER_SRGB:
+      if (val <= 0.0031308)
+        res = 12.92 * val;
+      else
+        res = 1.055 * pow (val, 1.0 / 2.4) - 0.055;
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA28:
+      res = pow (val, 1 / 2.8);
+      break;
+    case GST_VIDEO_TRANSFER_LOG100:
+      if (val < 0.01)
+        res = 0.0;
+      else
+        res = 1.0 + log10 (val) / 2.0;
+      break;
+    case GST_VIDEO_TRANSFER_LOG316:
+      if (val < 0.0031622777)
+        res = 0.0;
+      else
+        res = 1.0 + log10 (val) / 2.5;
+      break;
+  }
+  return res;
+}
+
+/**
+ * gst_video_color_transfer_decode:
+ * @func: a #GstVideoTransferFunction
+ * @val: a value
+ *
+ * Convert @val to its gamma decoded value. This is the inverse operation of
+ * @gst_video_color_transfer_encode().
+ *
+ * For a non-linear value L' in the range [0..1], conversion to the linear
+ * L is in general performed with a power function like:
+ *
+ * |[
+ *    L = L' ^ gamma
+ * ]|
+ *
+ * Depending on @func, different formulas might be applied. Some formulas
+ * encode a linear segment in the lower range.
+ *
+ * Returns: the gamme decoded value of @val
+ *
+ * Since: 1.6
+ */
+gdouble
+gst_video_color_transfer_decode (GstVideoTransferFunction func, gdouble val)
+{
+  gdouble res;
+
+  switch (func) {
+    case GST_VIDEO_TRANSFER_UNKNOWN:
+    case GST_VIDEO_TRANSFER_GAMMA10:
+    default:
+      res = val;
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA18:
+      res = pow (val, 1.8);
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA20:
+      res = pow (val, 2.0);
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA22:
+      res = pow (val, 2.2);
+      break;
+    case GST_VIDEO_TRANSFER_BT709:
+      if (val < 0.081)
+        res = val / 4.5;
+      else
+        res = pow ((val + 0.099) / 1.099, 1.0 / 0.45);
+      break;
+    case GST_VIDEO_TRANSFER_SMPTE240M:
+      if (val < 0.0913)
+        res = val / 4.0;
+      else
+        res = pow ((val + 0.1115) / 1.1115, 1.0 / 0.45);
+      break;
+    case GST_VIDEO_TRANSFER_SRGB:
+      if (val <= 0.04045)
+        res = val / 12.92;
+      else
+        res = pow ((val + 0.055) / 1.055, 2.4);
+      break;
+    case GST_VIDEO_TRANSFER_GAMMA28:
+      res = pow (val, 2.8);
+      break;
+    case GST_VIDEO_TRANSFER_LOG100:
+      if (val == 0.0)
+        res = 0.0;
+      else
+        res = pow (10.0, 2.0 * (val - 1.0));
+      break;
+    case GST_VIDEO_TRANSFER_LOG316:
+      if (val == 0.0)
+        res = 0.0;
+      else
+        res = pow (10.0, 2.5 * (val - 1.0));
+      break;
+  }
+  return res;
+}

gst-libs/gst/video/video-color.h

@@ -101,6 +101,9 @@ typedef enum {
   GST_VIDEO_TRANSFER_LOG316
 } GstVideoTransferFunction;
 
+gdouble      gst_video_color_transfer_encode (GstVideoTransferFunction func, gdouble val);
+gdouble      gst_video_color_transfer_decode (GstVideoTransferFunction func, gdouble val);
+
 /**
  * GstVideoColorPrimaries:
  * @GST_VIDEO_COLOR_PRIMARIES_UNKNOWN: unknown color primaries

tests/check/libs/video.c

@@ -2251,6 +2251,32 @@ GST_END_TEST;
 #undef WIDTH
 #undef HEIGHT
 
+GST_START_TEST (test_video_transfer)
+{
+  gint i, j;
+
+  for (j = GST_VIDEO_TRANSFER_GAMMA10; j <= GST_VIDEO_TRANSFER_LOG316; j++) {
+    for (i = 0; i < 256; i++) {
+      gdouble val1, val2;
+
+      val1 = gst_video_color_transfer_encode (j, i / 255.0);
+      fail_if (val1 < 0.0 || val1 > 1.0);
+
+      val2 = gst_video_color_transfer_decode (j, val1);
+      fail_if (val2 < 0.0 || val2 > 1.0);
+
+      GST_DEBUG ("%d: %d %f->%f->%f %d", j, i, i / 255.0, val1, val2,
+          (int) lrint (val2 * 255.0));
+      if (val1 == 0.0)
+        fail_if (val2 != 0.0);
+      else
+        fail_if (lrint (val2 * 255.0) != i);
+    }
+  }
+}
+
+GST_END_TEST;
+
 static Suite *
 video_suite (void)
 {
@@ -2279,6 +2305,7 @@ video_suite (void)
   tcase_add_test (tc_chain, test_video_scaler);
   tcase_add_test (tc_chain, test_video_color_convert);
   tcase_add_test (tc_chain, test_video_size_convert);
+  tcase_add_test (tc_chain, test_video_transfer);
 
   return s;
 }