detect and merge similar segments

similar = same quant and filter strength.
This save some bits in the segment map

Change-Id: I6f594474ad82bddf013278d47089e43a02e07e63

src/enc/analysis.c

@@ -68,47 +68,7 @@ static void SmoothSegmentMap(VP8Encoder* const enc) {
 }
 
 //------------------------------------------------------------------------------
-// Finalize Segment probability based on the coding tree
-
-static int GetProba(int a, int b) {
-  int proba;
-  const int total = a + b;
-  if (total == 0) return 255;  // that's the default probability.
-  proba = (255 * a + total / 2) / total;
-  return proba;
-}
-
-static void SetSegmentProbas(VP8Encoder* const enc) {
-  int p[NUM_MB_SEGMENTS] = { 0 };
-  int n;
-
-  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
-    const VP8MBInfo* const mb = &enc->mb_info_[n];
-    p[mb->segment_]++;
-  }
-  if (enc->pic_->stats) {
-    for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
-      enc->pic_->stats->segment_size[n] = p[n];
-    }
-  }
-  if (enc->segment_hdr_.num_segments_ > 1) {
-    uint8_t* const probas = enc->proba_.segments_;
-    probas[0] = GetProba(p[0] + p[1], p[2] + p[3]);
-    probas[1] = GetProba(p[0], p[1]);
-    probas[2] = GetProba(p[2], p[3]);
-
-    enc->segment_hdr_.update_map_ =
-        (probas[0] != 255) || (probas[1] != 255) || (probas[2] != 255);
-    enc->segment_hdr_.size_ =
-      p[0] * (VP8BitCost(0, probas[0]) + VP8BitCost(0, probas[1])) +
-      p[1] * (VP8BitCost(0, probas[0]) + VP8BitCost(1, probas[1])) +
-      p[2] * (VP8BitCost(1, probas[0]) + VP8BitCost(0, probas[2])) +
-      p[3] * (VP8BitCost(1, probas[0]) + VP8BitCost(1, probas[2]));
-  } else {
-    enc->segment_hdr_.update_map_ = 0;
-    enc->segment_hdr_.size_ = 0;
-  }
-}
+// set segment susceptibility alpha_ / beta_
 
 static WEBP_INLINE int clip(int v, int m, int M) {
   return (v < m) ? m : (v > M) ? M : v;
@@ -255,7 +215,6 @@ static void AssignSegments(VP8Encoder* const enc,
     if (smooth) SmoothSegmentMap(enc);
   }
 
-  SetSegmentProbas(enc);                             // Assign final proba
   SetSegmentAlphas(enc, centers, weighted_average);  // pick some alphas.
 }
 

src/enc/frame.c

@@ -211,6 +211,49 @@ static int FinalizeTokenProbas(VP8Encoder* const enc) {
   return size;
 }
 
+//------------------------------------------------------------------------------
+// Finalize Segment probability based on the coding tree
+
+static int GetProba(int a, int b) {
+  int proba;
+  const int total = a + b;
+  if (total == 0) return 255;  // that's the default probability.
+  proba = (255 * a + total / 2) / total;
+  return proba;
+}
+
+static void SetSegmentProbas(VP8Encoder* const enc) {
+  int p[NUM_MB_SEGMENTS] = { 0 };
+  int n;
+
+  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
+    const VP8MBInfo* const mb = &enc->mb_info_[n];
+    p[mb->segment_]++;
+  }
+  if (enc->pic_->stats != NULL) {
+    for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
+      enc->pic_->stats->segment_size[n] = p[n];
+    }
+  }
+  if (enc->segment_hdr_.num_segments_ > 1) {
+    uint8_t* const probas = enc->proba_.segments_;
+    probas[0] = GetProba(p[0] + p[1], p[2] + p[3]);
+    probas[1] = GetProba(p[0], p[1]);
+    probas[2] = GetProba(p[2], p[3]);
+
+    enc->segment_hdr_.update_map_ =
+        (probas[0] != 255) || (probas[1] != 255) || (probas[2] != 255);
+    enc->segment_hdr_.size_ =
+      p[0] * (VP8BitCost(0, probas[0]) + VP8BitCost(0, probas[1])) +
+      p[1] * (VP8BitCost(0, probas[0]) + VP8BitCost(1, probas[1])) +
+      p[2] * (VP8BitCost(1, probas[0]) + VP8BitCost(0, probas[2])) +
+      p[3] * (VP8BitCost(1, probas[0]) + VP8BitCost(1, probas[2]));
+  } else {
+    enc->segment_hdr_.update_map_ = 0;
+    enc->segment_hdr_.size_ = 0;
+  }
+}
+
 //------------------------------------------------------------------------------
 // helper functions for residuals struct VP8Residual.
 
@@ -849,6 +892,7 @@ static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
   }
 
   VP8SetSegmentParams(enc, q);      // setup segment quantizations and filters
+  SetSegmentProbas(enc);            // compute segment probabilities
 
   ResetStats(enc);
   ResetTokenStats(enc);

src/enc/quant.c

@@ -229,10 +229,50 @@ static double QualityToCompression(double q) {
   return (c < 0.75) ? c * (2. / 3.) : 2. * c - 1.;
 }
 
+static int SegmentsAreEquivalent(const VP8SegmentInfo* const S1,
+                                 const VP8SegmentInfo* const S2) {
+  return (S1->quant_ == S2->quant_) && (S1->fstrength_ == S2->fstrength_);
+}
+
+static void SimplifySegments(VP8Encoder* const enc) {
+  int map[NUM_MB_SEGMENTS] = { 0, 1, 2, 3 };
+  const int num_segments = enc->segment_hdr_.num_segments_;
+  int num_final_segments = 1;
+  int s1, s2;
+  for (s1 = 1; s1 < num_segments; ++s1) {    // find similar segments
+    const VP8SegmentInfo* const S1 = &enc->dqm_[s1];
+    int found = 0;
+    // check if we already have similar segment
+    for (s2 = 0; s2 < num_final_segments; ++s2) {
+      const VP8SegmentInfo* const S2 = &enc->dqm_[s2];
+      if (SegmentsAreEquivalent(S1, S2)) {
+        found = 1;
+        break;
+      }
+    }
+    map[s1] = s2;
+    if (!found) {
+      if (num_final_segments != s1) {
+        enc->dqm_[num_final_segments] = enc->dqm_[s1];
+      }
+      ++num_final_segments;
+    }
+  }
+  if (num_final_segments < num_segments) {  // Remap
+    int i = enc->mb_w_* enc->mb_h_;
+    while (i-- > 0) enc->mb_info_[i].segment_ = map[enc->mb_info_[i].segment_];
+    enc->segment_hdr_.num_segments_ = num_final_segments;
+    // Replicate the trailing segment infos (it's mostly cosmetics)
+    for (i = num_final_segments; i < num_segments; ++i) {
+      enc->dqm_[i] = enc->dqm_[num_final_segments - 1];
+    }
+  }
+}
+
 void VP8SetSegmentParams(VP8Encoder* const enc, float quality) {
   int i;
   int dq_uv_ac, dq_uv_dc;
-  const int num_segments = enc->config_->segments;
+  const int num_segments = enc->segment_hdr_.num_segments_;
   const double amp = SNS_TO_DQ * enc->config_->sns_strength / 100. / 128.;
   const double c_base = QualityToCompression(quality);
   for (i = 0; i < num_segments; ++i) {
@@ -281,9 +321,11 @@ void VP8SetSegmentParams(VP8Encoder* const enc, float quality) {
   enc->dq_uv_dc_ = dq_uv_dc;
   enc->dq_uv_ac_ = dq_uv_ac;
 
-  SetupMatrices(enc);
-
   SetupFilterStrength(enc);   // initialize segments' filtering, eventually
+
+  if (num_segments > 1) SimplifySegments(enc);
+
+  SetupMatrices(enc);         // finalize quantization matrices
 }
 
 //------------------------------------------------------------------------------