External denoiser based on noise estimation and moving object detection.

webrtc/modules/video_processing/util/noise_estimation.cc

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/video_processing/util/noise_estimation.h"
+
+namespace webrtc {
+
+void NoiseEstimation::Init(int width, int height, CpuType cpu_type) {
+  int mb_cols = width >> 4;
+  int mb_rows = height >> 4;
+  consec_low_var_.reset(new uint32_t[mb_cols * mb_rows]());
+  width_ = width;
+  height_ = height;
+  mb_cols_ = width_ >> 4;
+  mb_rows_ = height_ >> 4;
+  cpu_type_ = cpu_type;
+}
+
+void NoiseEstimation::GetNoise(int mb_index, uint32_t var, uint32_t luma) {
+  consec_low_var_[mb_index]++;
+  num_static_block_++;
+  if (consec_low_var_[mb_index] >= kConsecLowVarFrame &&
+      (luma >> 8) < kAverageLumaMax && (luma >> 8) > kAverageLumaMin) {
+    // Normalized var by the average luma value, this gives more credit to

[marpan, 2016/03/31 18:36:47]

weight?

[jackychen_, 2016/04/01 00:05:06]

Done.

+    // darker blocks.
+    int nor_var = var / (luma >> 12);
+    noise_var_ +=
+        nor_var > kBlockSelectionVarMax ? kBlockSelectionVarMax : nor_var;
+    num_noisy_block_++;
+  }
+}
+
+void NoiseEstimation::ResetConsecLowVar(int mb_index) {
+  consec_low_var_[mb_index] = 0;
+}
+
+void NoiseEstimation::UpdateNoiseLevel() {
+  // No enough samples implies the motion of the camera or too many moving
+  // objects in the frame.
+  if (num_static_block_ < (0.65 * mb_cols_ * mb_rows_) || !num_noisy_block_) {

[marpan, 2016/03/31 18:36:47]

look into why not "num_noisy_block_ < T"

[jackychen_, 2016/04/01 00:05:06]

Done.

+    noise_var_ = 0;
+    noise_var_accum_ = 0;
+    num_static_block_ = 0;
+    num_noisy_block_ = 0;
+#if DISPLAY
+    printf("Not enough samples.\n");
+#endif
+    return;
+  } else {
+    // Normalized by the number of noisy blocks.
+    noise_var_ /= num_noisy_block_;
+    // Get the percentage of static blocks.
+    percent_static_block_ =
+        static_cast<double>(num_static_block_) / (mb_cols_ * mb_rows_);
+#if DISPLAY
+    printf("%d %d fraction = %.3f\n", num_static_block_, mb_cols_ * mb_rows_,
+           percent_static_block_);
+#endif
+    num_noisy_block_ = 0;
+    num_static_block_ = 0;
+  }
+  // For the first frame just update the value with current noise_var_,
+  // otherwise, use the averaging window.
+  if (noise_var_accum_ == 0) {
+    noise_var_accum_ = noise_var_;
+  } else {
+    noise_var_accum_ = (noise_var_accum_ * 15 + noise_var_) / 16;
+  }
+  // Reset noise_var_ for the next frame.
+  noise_var_ = 0;
+#if DISPLAY
+  printf("noise_var_accum_ = %.1f, noise_var_ = %d.\n", noise_var_accum_,
+         noise_var_);
+#endif
+}
+
+uint8_t NoiseEstimation::GetNoiseLevel() {
+  int noise_thr = cpu_type_ ? kNoiseThreshold : kNoiseThresholdNeon;
+  UpdateNoiseLevel();
+  if (noise_var_accum_ > noise_thr) {
+    return 1;
+  }
+  return 0;
+}
+
+}  // namespace webrtc