Simplify Segment Coding

Remove top node optimization.
The improvement this gives is not sufficient to justify
the extra complexity.

Change-Id: I2bb4a12a50ffd52cacfa4a3e8acbb2e522066905

vp9/common/vp9_blockd.h

@@ -399,7 +399,6 @@ typedef struct macroblockd {
 
   // Probability Tree used to code Segment number
   vp9_prob mb_segment_tree_probs[MB_FEATURE_TREE_PROBS];
-  vp9_prob mb_segment_mispred_tree_probs[MAX_MB_SEGMENTS];
 
   // Segment features
   signed char segment_feature_data[MAX_MB_SEGMENTS][SEG_LVL_MAX];

vp9/decoder/vp9_decodemv.c

@@ -79,21 +79,6 @@ static int read_mb_segid(vp9_reader *r, MACROBLOCKD *xd) {
                            :     vp9_read(r, p[1]);
 }
 
-// This function reads the current macro block's segnent id from the bitstream
-// It should only be called if a segment map update is indicated.
-static int read_mb_segid_except(vp9_reader *r,
-                                VP9_COMMON *cm, MACROBLOCKD *xd,
-                                int mb_row, int mb_col) {
-  const BLOCK_SIZE_TYPE sb_type = xd->mode_info_context->mbmi.sb_type;
-  const int pred_seg_id = vp9_get_pred_mb_segid(cm, sb_type, mb_row, mb_col);
-  const vp9_prob *const p = xd->mb_segment_tree_probs;
-  const vp9_prob prob = xd->mb_segment_mispred_tree_probs[pred_seg_id];
-
-  return vp9_read(r, prob)
-             ? 2 + (pred_seg_id  < 2 ? vp9_read(r, p[2]) : (pred_seg_id == 2))
-             :     (pred_seg_id >= 2 ? vp9_read(r, p[1]) : (pred_seg_id == 0));
-}
-
 static void set_segment_id(VP9_COMMON *cm, MB_MODE_INFO *mbmi,
                            int mb_row, int mb_col, int segment_id) {
   const int mb_index = mb_row * cm->mb_cols + mb_col;
@@ -551,7 +536,7 @@ static int read_mb_segment_id(VP9D_COMP *pbi, int mb_row, int mb_col,
       // then use the predicted value, otherwise decode it explicitly
       segment_id = pred_flag ? vp9_get_pred_mb_segid(cm, mbmi->sb_type,
                                                      mb_row, mb_col)
-                             : read_mb_segid_except(r, cm, xd, mb_row, mb_col);
+                             : read_mb_segid(r, xd);
     } else {
       segment_id = read_mb_segid(r, xd);  // Normal unpredicted coding mode
     }

vp9/decoder/vp9_decodframe.c

@@ -1113,19 +1113,6 @@ static void setup_segmentation(VP9_COMMON *pc, MACROBLOCKD *xd, vp9_reader *r) {
 
     pc->temporal_update = vp9_read_bit(r);
     if (pc->temporal_update) {
-      const vp9_prob *p = xd->mb_segment_tree_probs;
-      vp9_prob *mispred_p = xd->mb_segment_mispred_tree_probs;
-
-      const int c0 =        p[0]  *        p[1];
-      const int c1 =        p[0]  * (256 - p[1]);
-      const int c2 = (256 - p[0]) *        p[2];
-      const int c3 = (256 - p[0]) * (256 - p[2]);
-
-      mispred_p[0] = get_binary_prob(c1, c2 + c3);
-      mispred_p[1] = get_binary_prob(c0, c2 + c3);
-      mispred_p[2] = get_binary_prob(c0 + c1, c3);
-      mispred_p[3] = get_binary_prob(c0 + c1, c2);
-
       for (i = 0; i < PREDICTION_PROBS; i++)
         pc->segment_pred_probs[i] = vp9_read_bit(r) ? vp9_read_prob(r)
                                                     : MAX_PROB;

vp9/encoder/vp9_bitstream.c

@@ -560,28 +560,6 @@ static void write_mb_segid(vp9_writer *bc,
   }
 }
 
-static void write_mb_segid_except(VP9_COMMON *cm,
-                                  vp9_writer *bc,
-                                  const MB_MODE_INFO *mi,
-                                  const MACROBLOCKD *xd,
-                                  int mb_row, int mb_col) {
-  // Encode the MB segment id.
-  const int seg_id = mi->segment_id;
-  const BLOCK_SIZE_TYPE sb_type = xd->mode_info_context->mbmi.sb_type;
-  const int pred_seg_id = vp9_get_pred_mb_segid(cm, sb_type, mb_row, mb_col);
-  const vp9_prob *p = xd->mb_segment_tree_probs;
-  const vp9_prob p1 = xd->mb_segment_mispred_tree_probs[pred_seg_id];
-
-  if (xd->segmentation_enabled && xd->update_mb_segmentation_map) {
-    vp9_write(bc, seg_id >= 2, p1);
-    if (pred_seg_id >= 2 && seg_id < 2) {
-      vp9_write(bc, seg_id == 1, p[1]);
-    } else if (pred_seg_id < 2 && seg_id >= 2) {
-      vp9_write(bc, seg_id == 3, p[2]);
-    }
-  }
-}
-
 // This function encodes the reference frame
 static void encode_ref_frame(vp9_writer *const bc,
                              VP9_COMMON *const cm,
@@ -725,7 +703,7 @@ static void pack_inter_mode_mvs(VP9_COMP *cpi, MODE_INFO *m,
 
       // If the mb segment id wasn't predicted code explicitly
       if (!prediction_flag)
-        write_mb_segid_except(pc, bc, mi, &cpi->mb.e_mbd, mb_row, mb_col);
+        write_mb_segid(bc, mi, &cpi->mb.e_mbd);
     } else {
       // Normal unpredicted coding
       write_mb_segid(bc, mi, &cpi->mb.e_mbd);

vp9/encoder/vp9_segmentation.c

@@ -103,8 +103,7 @@ static int cost_segmap(MACROBLOCKD *xd,
 // Based on set of segment counts calculate a probability tree
 static void calc_segtree_probs_pred(MACROBLOCKD *xd,
                                     int (*segcounts)[MAX_MB_SEGMENTS],
-                                    vp9_prob *segment_tree_probs,
+                                    vp9_prob *segment_tree_probs) {
-                                    vp9_prob *mod_probs) {
   int count[4];
 
   assert(!segcounts[0][0] && !segcounts[1][1] &&
@@ -121,24 +120,12 @@ static void calc_segtree_probs_pred(MACROBLOCKD *xd,
                                           count[2] + count[3]);
   segment_tree_probs[1] = get_binary_prob(count[0], count[1]);
   segment_tree_probs[2] = get_binary_prob(count[2], count[3]);
-
-  // now work out modified counts that the decoder would have
-  count[0] =        segment_tree_probs[0]  *        segment_tree_probs[1];
-  count[1] =        segment_tree_probs[0]  * (256 - segment_tree_probs[1]);
-  count[2] = (256 - segment_tree_probs[0]) *        segment_tree_probs[2];
-  count[3] = (256 - segment_tree_probs[0]) * (256 - segment_tree_probs[2]);
-
-  // Work out modified probabilties depending on what segment was predicted
-  mod_probs[0] = get_binary_prob(count[1], count[2] + count[3]);
-  mod_probs[1] = get_binary_prob(count[0], count[2] + count[3]);
-  mod_probs[2] = get_binary_prob(count[0] + count[1], count[3]);
-  mod_probs[3] = get_binary_prob(count[0] + count[1], count[2]);
 }
 
 // Based on set of segment counts and probabilities calculate a cost estimate
 static int cost_segmap_pred(MACROBLOCKD *xd,
                             int (*segcounts)[MAX_MB_SEGMENTS],
-                            vp9_prob *probs, vp9_prob *mod_probs) {
+                            vp9_prob *probs) {
   int pred_seg, cost = 0;
 
   for (pred_seg = 0; pred_seg < MAX_MB_SEGMENTS; pred_seg++) {
@@ -147,8 +134,8 @@ static int cost_segmap_pred(MACROBLOCKD *xd,
     // Cost the top node of the tree
     count1 = segcounts[pred_seg][0] + segcounts[pred_seg][1];
     count2 = segcounts[pred_seg][2] + segcounts[pred_seg][3];
-    cost += count1 * vp9_cost_zero(mod_probs[pred_seg]) +
+    cost += count1 * vp9_cost_zero(probs[0]) +
-            count2 * vp9_cost_one(mod_probs[pred_seg]);
+            count2 * vp9_cost_one(probs[0]);
 
     // Now add the cost of each individual segment branch
     if (pred_seg >= 2 && count1) {
@@ -217,7 +204,6 @@ void vp9_choose_segmap_coding_method(VP9_COMP *cpi) {
 
   vp9_prob no_pred_tree[MB_FEATURE_TREE_PROBS];
   vp9_prob t_pred_tree[MB_FEATURE_TREE_PROBS];
-  vp9_prob t_pred_tree_mod[MAX_MB_SEGMENTS];
   vp9_prob t_nopred_prob[PREDICTION_PROBS];
 
   const int mis = cm->mode_info_stride;
@@ -332,10 +318,8 @@ void vp9_choose_segmap_coding_method(VP9_COMP *cpi) {
   if (cm->frame_type != KEY_FRAME) {
     // Work out probability tree for coding those segments not
     // predicted using the temporal method and the cost.
-    calc_segtree_probs_pred(xd, t_unpred_seg_counts, t_pred_tree,
+    calc_segtree_probs_pred(xd, t_unpred_seg_counts, t_pred_tree);
-                            t_pred_tree_mod);
+    t_pred_cost = cost_segmap_pred(xd, t_unpred_seg_counts, t_pred_tree);
-    t_pred_cost = cost_segmap_pred(xd, t_unpred_seg_counts, t_pred_tree,
-                                   t_pred_tree_mod);
 
     // Add in the cost of the signalling for each prediction context
     for (i = 0; i < PREDICTION_PROBS; i++) {
@@ -355,8 +339,6 @@ void vp9_choose_segmap_coding_method(VP9_COMP *cpi) {
     cm->temporal_update = 1;
     vpx_memcpy(xd->mb_segment_tree_probs,
                t_pred_tree, sizeof(t_pred_tree));
-    vpx_memcpy(xd->mb_segment_mispred_tree_probs,
-               t_pred_tree_mod, sizeof(t_pred_tree_mod));
     vpx_memcpy(&cm->segment_pred_probs,
                t_nopred_prob, sizeof(t_nopred_prob));
   } else {