External denoiser based on noise estimation and moving object detection.

webrtc/modules/video_processing/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/noise_estimation.h"
+
+namespace webrtc {
+
+void NoiseEstimation::SetResolution(int width, int height) {
+  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;
+}
+
+void NoiseEstimation::GetNoise(int mb_index, uint32_t var, uint32_t luma) {
+  consec_low_var_[mb_index]++;
+  num_stationary_block_++;
+  if (consec_low_var_[mb_index] >= 6 && (luma >> 8) < 220 && (luma >> 8) > 20) {

[marpan, 2016/03/24 20:56:16]

i would prefer to expose these thresholds (6, 229, 290, 384) as parameters
of model, with name that explains its meaning.

[jackychen_, 2016/03/25 18:45:44]

Done.

+    noise_var_ += ((var / (luma >> 12)) > 384) ? 384 : (var / (luma >> 12));
+    num_noisy_block_++;
+  }
+}
+
+void NoiseEstimation::ResetConsecLowVar(int mb_index) {
+  consec_low_var_[mb_index] = 0;
+}
+
+uint8_t NoiseEstimation::GetNoiseLevel() {
+  int mb_cols = width_ >> 4;
+  int mb_rows = height_ >> 4;
+  // No enough samples implies the motion of the camera.

[marpan, 2016/03/24 20:56:16]

...or too much of object in frame

[jackychen_, 2016/03/25 18:45:44]

Done.

+  if (num_stationary_block_ < 0.75 * mb_cols * mb_rows || !num_noisy_block_) {
+    noise_var_ = 0;
+    noise_var_accum_ = 0;
+    num_stationary_block_ = 0;
+    num_noisy_block_ = 0;
+#if DISPLAY
+    printf("Not enough samples.\n");
+#endif
+    return 0;
+  } else {
+    noise_var_ /= num_noisy_block_;
+    percent_non_montion_block_ =
+        static_cast<double>(num_stationary_block_) / (mb_cols * mb_rows);
+#if DISPLAY
+    printf("%d %d fraction = %.3f\n", num_stationary_block_, mb_cols * mb_rows,
+           percent_non_montion_block_);
+#endif
+    num_noisy_block_ = 0;
+    num_stationary_block_ = 0;
+  }
+  // For the first frame get the noise value, just use the value as accumulated
+  // one, 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;

[marpan, 2016/03/24 20:56:16]

better to expose this (15) as parameter too?

[jackychen_, 2016/03/25 18:45:44]

Acknowledged.

+  }
+#if DISPLAY
+  printf("noise_var_accum_ = %.1f, noise_var_ = %d.\n", noise_var_accum_,
+         noise_var_);
+#endif
+  // Reset noise_var_ for the next frame.
+  noise_var_ = 0;
+  if (noise_var_accum_ > kNoiseThresholdHigh) {
+    return 2;
+  } else if (noise_var_accum_ > kNoiseThreshold) {
+    return 1;
+  }
+  return 0;
+}
+
+}  // namespace webrtc