video-color: add gst_video_color_matrix_get_Kr_Kb()

Move the function to get the color matrix coefficients from
videoconvert to the video library.

docs/libs/gst-plugins-base-libs-sections.txt

@@ -2299,6 +2299,7 @@ gst_video_colorimetry_matches
 gst_video_colorimetry_from_string
 gst_video_colorimetry_to_string
 gst_video_color_range_offsets
+gst_video_color_matrix_get_Kr_Kb
 <SUBSECTION Standard>
 gst_video_color_range_get_type
 GST_TYPE_VIDEO_COLOR_RANGE

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

@@ -243,3 +243,74 @@ static const PrimariesInfo primaries[] = {
       0.049}
 };
 #endif
+
+/**
+ * gst_video_color_matrix_get_Kr_Kb:
+ * @matrix: a #GstVideoColorMatrix
+ * @Kr: result red channel coefficient
+ * @Kb: result blue channel coefficient
+ *
+ * Get the coefficients used to convert between Y'PbPr and R'G'B' using @matrix.
+ *
+ * When:
+ *
+ * |[
+ *   0.0 <= [Y',R',G',B'] <= 1.0)
+ *   (-0.5 <= [Pb,Pr] <= 0.5)
+ * ]|
+ *
+ * the general conversion is given by:
+ *
+ * |[
+ *   Y' = Kr*R' + (1-Kr-Kb)*G' + Kb*B'
+ *   Pb = (B'-Y')/(2*(1-Kb))
+ *   Pr = (R'-Y')/(2*(1-Kr))
+ * ]|
+ *
+ * and the other way around:
+ *
+ * |[
+ *   R' = Y' + Cr*2*(1-Kr)
+ *   G' = Y' - Cb*2*(1-Kb)*Kb/(1-Kr-Kb) - Cr*2*(1-Kr)*Kr/(1-Kr-Kb)
+ *   B' = Y' + Cb*2*(1-Kb)
+ * ]|
+ *
+ * Returns: TRUE if @matrix was a YUV color format and @Kr and @Kb contain valid
+ *    values.
+ *
+ * Since: 1.6
+ */
+gboolean
+gst_video_color_matrix_get_Kr_Kb (GstVideoColorMatrix matrix, gdouble * Kr,
+    gdouble * Kb)
+{
+  gboolean res = TRUE;
+
+  switch (matrix) {
+      /* RGB */
+    default:
+    case GST_VIDEO_COLOR_MATRIX_RGB:
+      res = FALSE;
+      break;
+      /* YUV */
+    case GST_VIDEO_COLOR_MATRIX_FCC:
+      *Kr = 0.30;
+      *Kb = 0.11;
+      break;
+    case GST_VIDEO_COLOR_MATRIX_BT709:
+      *Kr = 0.2126;
+      *Kb = 0.0722;
+      break;
+    case GST_VIDEO_COLOR_MATRIX_BT601:
+      *Kr = 0.2990;
+      *Kb = 0.1140;
+      break;
+    case GST_VIDEO_COLOR_MATRIX_SMPTE240M:
+      *Kr = 0.212;
+      *Kb = 0.087;
+      break;
+  }
+  GST_DEBUG ("matrix: %d, Kr %f, Kb %f", matrix, *Kr, *Kb);
+
+  return res;
+}

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

@@ -63,6 +63,8 @@ typedef enum {
   GST_VIDEO_COLOR_MATRIX_SMPTE240M
 } GstVideoColorMatrix;
 
+gboolean gst_video_color_matrix_get_Kr_Kb (GstVideoColorMatrix matrix, gdouble * Kr, gdouble * Kb);
+
 /**
  * GstVideoTransferFunction:
  * @GST_VIDEO_TRANSFER_UNKNOWN: unknown transfer function

gst/videoconvert/videoconvert.c

@@ -182,39 +182,6 @@ videoconvert_convert_matrix16 (VideoConvert * convert, gpointer pixels)
   }
 }
 
-static gboolean
-get_Kr_Kb (GstVideoColorMatrix matrix, gdouble * Kr, gdouble * Kb)
-{
-  gboolean res = TRUE;
-
-  switch (matrix) {
-      /* RGB */
-    default:
-    case GST_VIDEO_COLOR_MATRIX_RGB:
-      res = FALSE;
-      break;
-      /* YUV */
-    case GST_VIDEO_COLOR_MATRIX_FCC:
-      *Kr = 0.30;
-      *Kb = 0.11;
-      break;
-    case GST_VIDEO_COLOR_MATRIX_BT709:
-      *Kr = 0.2126;
-      *Kb = 0.0722;
-      break;
-    case GST_VIDEO_COLOR_MATRIX_BT601:
-      *Kr = 0.2990;
-      *Kb = 0.1140;
-      break;
-    case GST_VIDEO_COLOR_MATRIX_SMPTE240M:
-      *Kr = 0.212;
-      *Kb = 0.087;
-      break;
-  }
-  GST_DEBUG ("matrix: %d, Kr %f, Kb %f", matrix, *Kr, *Kb);
-  return res;
-}
-
 static gboolean
 videoconvert_convert_compute_matrix (VideoConvert * convert)
 {
@@ -283,7 +250,7 @@ videoconvert_convert_compute_matrix (VideoConvert * convert)
       1 / ((float) scale[1]), 1 / ((float) scale[2]));
 
   /* 2. bring components to R'G'B' space */
-  if (get_Kr_Kb (in_info->colorimetry.matrix, &Kr, &Kb))
+  if (gst_video_color_matrix_get_Kr_Kb (in_info->colorimetry.matrix, &Kr, &Kb))
     color_matrix_YCbCr_to_RGB (&dst, Kr, Kb);
 
   /* 3. inverse transfer function. R'G'B' to linear RGB */
@@ -295,7 +262,7 @@ videoconvert_convert_compute_matrix (VideoConvert * convert)
   /* 6. transfer function. linear RGB to R'G'B' */
 
   /* 7. bring components to YCbCr space */
-  if (get_Kr_Kb (out_info->colorimetry.matrix, &Kr, &Kb))
+  if (gst_video_color_matrix_get_Kr_Kb (out_info->colorimetry.matrix, &Kr, &Kb))
     color_matrix_RGB_to_YCbCr (&dst, Kr, Kb);
 
   /* 8, bring color components to nominal range */

win32/common/libgstvideo.def

@@ -71,6 +71,7 @@ EXPORTS
 	gst_video_codec_state_get_type
 	gst_video_codec_state_ref
 	gst_video_codec_state_unref
+	gst_video_color_matrix_get_Kr_Kb
 	gst_video_color_matrix_get_type
 	gst_video_color_primaries_get_type
 	gst_video_color_range_get_type