vp8: Remove isolated skin & non skin blocks.

Neutral on RTC metrics and speed on Pixel.

Change-Id: I26b907483fe133e6e4c1009d147631f0d0e0f2fb

1 files changed, 25 insertions, 3 deletions

diff --git a/vp8/encoder/onyx_if.c b/vp8/encoder/onyx_if.c
index b018ca61e..2b7f6795b 100644
--- a/vp8/encoder/onyx_if.c
+++ b/vp8/encoder/onyx_if.c
@@ -628,16 +628,15 @@ static void compute_skin_map(VP8_COMP *cpi) {
 
   const SKIN_DETECTION_BLOCK_SIZE bsize =
       (cm->Width * cm->Height <= 352 * 288) ? SKIN_8X8 : SKIN_16X16;
-  int offset = 0;
+
   for (mb_row = 0; mb_row < cm->mb_rows; mb_row++) {
     num_bl = 0;
     for (mb_col = 0; mb_col < cm->mb_cols; mb_col++) {
       const int bl_index = mb_row * cm->mb_cols + mb_col;
-      cpi->skin_map[offset] =
+      cpi->skin_map[bl_index] =
           vp8_compute_skin_block(src_y, src_u, src_v, src_ystride, src_uvstride,
                                  bsize, cpi->consec_zero_last[bl_index], 0);
       num_bl++;
-      offset++;
       src_y += 16;
       src_u += 8;
       src_v += 8;
@@ -646,6 +645,29 @@ static void compute_skin_map(VP8_COMP *cpi) {
     src_u += (src_uvstride << 3) - (num_bl << 3);
     src_v += (src_uvstride << 3) - (num_bl << 3);
   }
+
+  // Remove isolated skin blocks (none of its neighbors are skin) and isolated
+  // non-skin blocks (all of its neighbors are skin). Skip the boundary.
+  for (mb_row = 1; mb_row < cm->mb_rows - 1; mb_row++) {
+    for (mb_col = 1; mb_col < cm->mb_cols - 1; mb_col++) {
+      const int bl_index = mb_row * cm->mb_cols + mb_col;
+      int num_neighbor = 0;
+      int mi, mj;
+      int non_skin_threshold = 8;
+
+      for (mi = -1; mi <= 1; mi += 1) {
+        for (mj = -1; mj <= 1; mj += 1) {
+          int bl_neighbor_index = (mb_row + mi) * cm->mb_cols + mb_col + mj;
+          if (cpi->skin_map[bl_neighbor_index]) num_neighbor++;
+        }
+      }
+
+      if (cpi->skin_map[bl_index] && num_neighbor < 2)
+        cpi->skin_map[bl_index] = 0;
+      if (!cpi->skin_map[bl_index] && num_neighbor == non_skin_threshold)
+        cpi->skin_map[bl_index] = 1;
+    }
+  }
 }
 
 static void set_default_lf_deltas(VP8_COMP *cpi) {