videoconvert: tweak the scoring algorithm

Make a little table of conversions and manually score them. Use this
info to define better weights for the scoring algorithm.
give separate scores for doing changes and the impact of the change,
This allows us to avoid conversion when we can but still allow fairly
lossless changes.
The old code did not penalize GRAY conversions, PAL conversions were
punished too low and depth conversions too high.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=722656

1 files changed, 74 insertions, 24 deletions

diff --git a/gst/videoconvert/gstvideoconvert.c b/gst/videoconvert/gstvideoconvert.c
index f9b4495e4..34e353539 100644
--- a/gst/videoconvert/gstvideoconvert.c
+++ b/gst/videoconvert/gstvideoconvert.c
@@ -143,17 +143,49 @@ gst_video_convert_caps_remove_format_info (GstCaps * caps)
   return res;
 }
 
-#define SCORE_PALETTE_LOSS        1
-#define SCORE_COLOR_LOSS          2
-#define SCORE_ALPHA_LOSS          4
-#define SCORE_CHROMA_W_LOSS       8
-#define SCORE_CHROMA_H_LOSS      16
-#define SCORE_DEPTH_LOSS         32
-
-#define COLOR_MASK   (GST_VIDEO_FORMAT_FLAG_YUV | \
-                      GST_VIDEO_FORMAT_FLAG_RGB | GST_VIDEO_FORMAT_FLAG_GRAY)
-#define ALPHA_MASK   (GST_VIDEO_FORMAT_FLAG_ALPHA)
-#define PALETTE_MASK (GST_VIDEO_FORMAT_FLAG_PALETTE)
+/*
+ * This is an incomplete matrix of in formats and a score for the prefered output
+ * format.
+ *
+ *         out: RGB24   RGB16  ARGB  AYUV  YUV444  YUV422 YUV420 YUV411 YUV410  PAL  GRAY
+ *  in
+ * RGB24          0      2       1     2     2       3      4      5      6      7    8
+ * RGB16          1      0       1     2     2       3      4      5      6      7    8
+ * ARGB           2      3       0     1     4       5      6      7      8      9    10
+ * AYUV           3      4       1     0     2       5      6      7      8      9    10
+ * YUV444         2      4       3     1     0       5      6      7      8      9    10
+ * YUV422         3      5       4     2     1       0      6      7      8      9    10
+ * YUV420         4      6       5     3     2       1      0      7      8      9    10
+ * YUV411         4      6       5     3     2       1      7      0      8      9    10
+ * YUV410         6      8       7     5     4       3      2      1      0      9    10
+ * PAL            1      3       2     6     4       6      7      8      9      0    10
+ * GRAY           1      4       3     2     1       5      6      7      8      9    0
+ *
+ * PAL or GRAY are never prefered, if we can we would convert to PAL instead
+ * of GRAY, though
+ * less subsampling is prefered and if any, preferably horizontal
+ * We would like to keep the alpha, even if we would need to to colorspace conversion
+ * or lose depth.
+ */
+#define SCORE_FORMAT_CHANGE       1
+#define SCORE_DEPTH_CHANGE        1
+#define SCORE_ALPHA_CHANGE        1
+#define SCORE_CHROMA_W_CHANGE     1
+#define SCORE_CHROMA_H_CHANGE     1
+#define SCORE_PALETTE_CHANGE      1
+
+#define SCORE_COLORSPACE_LOSS     2     /* RGB <-> YUV */
+#define SCORE_DEPTH_LOSS          4     /* change bit depth */
+#define SCORE_ALPHA_LOSS          8     /* lose the alpha channel */
+#define SCORE_CHROMA_W_LOSS      16     /* vertical subsample */
+#define SCORE_CHROMA_H_LOSS      32     /* horizontal subsample */
+#define SCORE_PALETTE_LOSS       64     /* convert to palette format */
+#define SCORE_COLOR_LOSS        128     /* convert to GRAY */
+
+#define COLORSPACE_MASK (GST_VIDEO_FORMAT_FLAG_YUV | \
+                         GST_VIDEO_FORMAT_FLAG_RGB | GST_VIDEO_FORMAT_FLAG_GRAY)
+#define ALPHA_MASK      (GST_VIDEO_FORMAT_FLAG_ALPHA)
+#define PALETTE_MASK    (GST_VIDEO_FORMAT_FLAG_PALETTE)
 
 /* calculate how much loss a conversion would be */
 static void
@@ -177,7 +209,7 @@ score_value (GstBaseTransform * base, const GstVideoFormatInfo * in_info,
     return;
   }
 
-  loss = 1;
+  loss = SCORE_FORMAT_CHANGE;
 
   in_flags = GST_VIDEO_FORMAT_INFO_FLAGS (in_info);
   in_flags &= ~GST_VIDEO_FORMAT_FLAG_LE;
@@ -189,22 +221,40 @@ score_value (GstBaseTransform * base, const GstVideoFormatInfo * in_info,
   t_flags &= ~GST_VIDEO_FORMAT_FLAG_COMPLEX;
   t_flags &= ~GST_VIDEO_FORMAT_FLAG_UNPACK;
 
-  if ((t_flags & PALETTE_MASK) != (in_flags & PALETTE_MASK))
-    loss += SCORE_PALETTE_LOSS;
+  if ((t_flags & PALETTE_MASK) != (in_flags & PALETTE_MASK)) {
+    loss += SCORE_PALETTE_CHANGE;
+    if (t_flags & PALETTE_MASK)
+      loss += SCORE_PALETTE_LOSS;
+  }
 
-  if ((t_flags & COLOR_MASK) != (in_flags & COLOR_MASK))
-    loss += SCORE_COLOR_LOSS;
+  if ((t_flags & COLORSPACE_MASK) != (in_flags & COLORSPACE_MASK)) {
+    loss += SCORE_COLORSPACE_LOSS;
+    if (t_flags & GST_VIDEO_FORMAT_FLAG_GRAY)
+      loss += SCORE_COLOR_LOSS;
+  }
 
-  if ((t_flags & ALPHA_MASK) != (in_flags & ALPHA_MASK))
-    loss += SCORE_ALPHA_LOSS;
+  if ((t_flags & ALPHA_MASK) != (in_flags & ALPHA_MASK)) {
+    loss += SCORE_ALPHA_CHANGE;
+    if (in_flags & ALPHA_MASK)
+      loss += SCORE_ALPHA_LOSS;
+  }
 
-  if ((in_info->h_sub[1]) < (t_info->h_sub[1]))
-    loss += SCORE_CHROMA_H_LOSS;
-  if ((in_info->w_sub[1]) < (t_info->w_sub[1]))
-    loss += SCORE_CHROMA_W_LOSS;
+  if ((in_info->h_sub[1]) != (t_info->h_sub[1])) {
+    loss += SCORE_CHROMA_H_CHANGE;
+    if ((in_info->h_sub[1]) < (t_info->h_sub[1]))
+      loss += SCORE_CHROMA_H_LOSS;
+  }
+  if ((in_info->w_sub[1]) != (t_info->w_sub[1])) {
+    loss += SCORE_CHROMA_W_CHANGE;
+    if ((in_info->w_sub[1]) < (t_info->w_sub[1]))
+      loss += SCORE_CHROMA_W_LOSS;
+  }
 
-  if ((in_info->bits) > (t_info->bits))
-    loss += SCORE_DEPTH_LOSS;
+  if ((in_info->bits) != (t_info->bits)) {
+    loss += SCORE_DEPTH_CHANGE;
+    if ((in_info->bits) > (t_info->bits))
+      loss += SCORE_DEPTH_LOSS;
+  }
 
   GST_DEBUG_OBJECT (base, "score %s -> %s = %d",
       GST_VIDEO_FORMAT_INFO_NAME (in_info),