Adds a new temporal consistency metric to libvpx.

Change-Id: Id61699ebf57ae4f8af96a468740c852b2f45f8e1

test/consistency_test.cc

+/*
+ *  Copyright (c) 2012 The WebM 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 <string.h>
+#include <limits.h>
+#include <stdio.h>
+
+#include "./vpx_config.h"
+#if CONFIG_VP9_ENCODER
+#include "./vp9_rtcd.h"
+#endif
+
+#include "test/acm_random.h"
+#include "test/clear_system_state.h"
+#include "test/register_state_check.h"
+#include "test/util.h"
+#include "third_party/googletest/src/include/gtest/gtest.h"
+#include "vp9/encoder/vp9_ssim.h"
+#include "vpx_mem/vpx_mem.h"
+
+extern "C"
+double vp9_get_ssim_metrics(uint8_t *img1, int img1_pitch,
+                            uint8_t *img2, int img2_pitch,
+                            int width, int height,
+                            Ssimv *sv2, Metrics *m,
+                            int do_inconsistency);
+
+using libvpx_test::ACMRandom;
+
+namespace {
+class ConsistencyTestBase : public ::testing::Test {
+ public:
+  ConsistencyTestBase(int width, int height) : width_(width), height_(height) {}
+
+  static void SetUpTestCase() {
+    source_data_[0] = reinterpret_cast<uint8_t*>(
+        vpx_memalign(kDataAlignment, kDataBufferSize));
+    reference_data_[0] = reinterpret_cast<uint8_t*>(
+        vpx_memalign(kDataAlignment, kDataBufferSize));
+    source_data_[1] = reinterpret_cast<uint8_t*>(
+        vpx_memalign(kDataAlignment, kDataBufferSize));
+    reference_data_[1] = reinterpret_cast<uint8_t*>(
+        vpx_memalign(kDataAlignment, kDataBufferSize));
+    ssim_array_ = new Ssimv[kDataBufferSize / 16];
+  }
+
+  static void ClearSsim() {
+    memset(ssim_array_, 0, kDataBufferSize / 16);
+  }
+  static void TearDownTestCase() {
+    vpx_free(source_data_[0]);
+    source_data_[0] = NULL;
+    vpx_free(reference_data_[0]);
+    reference_data_[0] = NULL;
+    vpx_free(source_data_[1]);
+    source_data_[1] = NULL;
+    vpx_free(reference_data_[1]);
+    reference_data_[1] = NULL;
+
+    delete ssim_array_;
+  }
+
+  virtual void TearDown() {
+    libvpx_test::ClearSystemState();
+  }
+
+ protected:
+  // Handle frames up to 640x480
+  static const int kDataAlignment = 16;
+  static const int kDataBufferSize = 640*480;
+
+  virtual void SetUp() {
+    source_stride_ = (width_ + 31) & ~31;
+    reference_stride_ = width_ * 2;
+    rnd_.Reset(ACMRandom::DeterministicSeed());
+  }
+
+  void FillRandom(uint8_t *data, int stride, int width, int height) {
+    for (int h = 0; h < height; ++h) {
+      for (int w = 0; w < width; ++w) {
+        data[h * stride + w] = rnd_.Rand8();
+      }
+    }
+  }
+
+  void FillRandom(uint8_t *data, int stride) {
+    FillRandom(data, stride, width_, height_);
+  }
+
+  void Copy(uint8_t *reference, uint8_t *source) {
+    memcpy(reference, source, kDataBufferSize);
+  }
+
+  void Blur(uint8_t *data, int stride, int taps) {
+    int sum = 0;
+    int half_taps = taps / 2;
+    for (int h = 0; h < height_; ++h) {
+      for (int w = 0; w < taps; ++w) {
+        sum += data[w + h * stride];
+      }
+      for (int w = taps; w < width_; ++w) {
+        sum += data[w + h * stride] - data[w - taps + h * stride];
+        data[w - half_taps + h * stride] = (sum + half_taps) / taps;
+      }
+    }
+    for (int w = 0; w < width_; ++w) {
+      for (int h = 0; h < taps; ++h) {
+        sum += data[h + w * stride];
+      }
+      for (int h = taps; h < height_; ++h) {
+        sum += data[w + h * stride] - data[(h - taps) * stride + w];
+        data[(h - half_taps) * stride + w] = (sum + half_taps) / taps;
+      }
+    }
+  }
+  int width_, height_;
+  static uint8_t* source_data_[2];
+  int source_stride_;
+  static uint8_t* reference_data_[2];
+  int reference_stride_;
+  static Ssimv *ssim_array_;
+  Metrics metrics_;
+
+  ACMRandom rnd_;
+};
+
+#if CONFIG_VP9_ENCODER
+typedef std::tr1::tuple<int, int> ConsistencyParam;
+class ConsistencyVP9Test
+    : public ConsistencyTestBase,
+      public ::testing::WithParamInterface<ConsistencyParam> {
+ public:
+  ConsistencyVP9Test() : ConsistencyTestBase(GET_PARAM(0), GET_PARAM(1)) {}
+
+ protected:
+  double CheckConsistency(int frame) {
+    EXPECT_LT(frame, 2)<< "Frame to check has to be less than 2.";
+    return
+        vp9_get_ssim_metrics(source_data_[frame], source_stride_,
+                             reference_data_[frame], reference_stride_,
+                             width_, height_, ssim_array_, &metrics_, 1);
+  }
+};
+#endif  // CONFIG_VP9_ENCODER
+
+uint8_t* ConsistencyTestBase::source_data_[2] = {NULL, NULL};
+uint8_t* ConsistencyTestBase::reference_data_[2] = {NULL, NULL};
+Ssimv* ConsistencyTestBase::ssim_array_ = NULL;
+
+#if CONFIG_VP9_ENCODER
+TEST_P(ConsistencyVP9Test, ConsistencyIsZero) {
+  FillRandom(source_data_[0], source_stride_);
+  Copy(source_data_[1], source_data_[0]);
+  Copy(reference_data_[0], source_data_[0]);
+  Blur(reference_data_[0], reference_stride_, 3);
+  Copy(reference_data_[1], source_data_[0]);
+  Blur(reference_data_[1], reference_stride_, 3);
+
+  double inconsistency = CheckConsistency(1);
+  inconsistency = CheckConsistency(0);
+  EXPECT_EQ(inconsistency, 0.0)
+      << "Should have 0 inconsistency if they are exactly the same.";
+
+  // If sources are not consistent reference frames inconsistency should
+  // be less than if the source is consistent.
+  FillRandom(source_data_[0], source_stride_);
+  FillRandom(source_data_[1], source_stride_);
+  FillRandom(reference_data_[0], reference_stride_);
+  FillRandom(reference_data_[1], reference_stride_);
+  CheckConsistency(0);
+  inconsistency = CheckConsistency(1);
+
+  Copy(source_data_[1], source_data_[0]);
+  CheckConsistency(0);
+  double inconsistency2 = CheckConsistency(1);
+  EXPECT_LT(inconsistency, inconsistency2)
+      << "Should have less inconsistency if source itself is inconsistent.";
+
+  // Less of a blur should be less inconsistent than more blur coming off a
+  // a frame with no blur.
+  ClearSsim();
+  FillRandom(source_data_[0], source_stride_);
+  Copy(source_data_[1], source_data_[0]);
+  Copy(reference_data_[0], source_data_[0]);
+  Copy(reference_data_[1], source_data_[0]);
+  Blur(reference_data_[1], reference_stride_, 4);
+  CheckConsistency(0);
+  inconsistency = CheckConsistency(1);
+  ClearSsim();
+  Copy(reference_data_[1], source_data_[0]);
+  Blur(reference_data_[1], reference_stride_, 8);
+  CheckConsistency(0);
+  inconsistency2 = CheckConsistency(1);
+
+  EXPECT_LT(inconsistency, inconsistency2)
+      << "Stronger Blur should produce more inconsistency.";
+}
+#endif  // CONFIG_VP9_ENCODER
+
+
+using std::tr1::make_tuple;
+
+//------------------------------------------------------------------------------
+// C functions
+
+#if CONFIG_VP9_ENCODER
+const ConsistencyParam c_vp9_tests[] = {
+  make_tuple(320, 240),
+  make_tuple(318, 242),
+  make_tuple(318, 238),
+};
+INSTANTIATE_TEST_CASE_P(C, ConsistencyVP9Test,
+                        ::testing::ValuesIn(c_vp9_tests));
+#endif
+
+}  // namespace

test/test.mk

@@ -151,6 +151,8 @@ LIBVPX_TEST_SRCS-$(CONFIG_VP9)         += vp9_intrapred_test.cc
 ifeq ($(CONFIG_VP9_ENCODER),yes)
 LIBVPX_TEST_SRCS-$(CONFIG_SPATIAL_SVC) += svc_test.cc
 LIBVPX_TEST_SRCS-$(CONFIG_INTERNAL_STATS) += blockiness_test.cc
+LIBVPX_TEST_SRCS-$(CONFIG_INTERNAL_STATS) += consistency_test.cc
+
 endif
 
 ifeq ($(CONFIG_VP9_ENCODER)$(CONFIG_VP9_TEMPORAL_DENOISING),yesyes)

vp9/encoder/vp9_encoder.c

@@ -1618,7 +1618,8 @@ VP9_COMP *vp9_create_compressor(VP9EncoderConfig *oxcf,
 #if CONFIG_INTERNAL_STATS
   cpi->b_calculate_ssimg = 0;
   cpi->b_calculate_blockiness = 1;
-
+  cpi->b_calculate_consistency = 1;
+  cpi->total_inconsistency = 0;
 
   cpi->count = 0;
   cpi->bytes = 0;
@@ -1669,6 +1670,10 @@ VP9_COMP *vp9_create_compressor(VP9EncoderConfig *oxcf,
     cpi->total_blockiness = 0;
   }
 
+  if (cpi->b_calculate_consistency) {
+    cpi->ssim_vars = vpx_malloc(sizeof(*cpi->ssim_vars)*720*480);
+  }
+
 #endif
 
   cpi->first_time_stamp_ever = INT64_MAX;
@@ -1865,6 +1870,12 @@ VP9_COMP *vp9_create_compressor(VP9EncoderConfig *oxcf,
 
   return cpi;
 }
+#define SNPRINT(H, T) \
+  snprintf((H) + strlen(H), sizeof(H) - strlen(H), (T))
+
+#define SNPRINT2(H, T, V) \
+  snprintf((H) + strlen(H), sizeof(H) - strlen(H), (T), (V))
+
 
 void vp9_remove_compressor(VP9_COMP *cpi) {
   VP9_COMMON *const cm = &cpi->common;
@@ -1878,8 +1889,9 @@ void vp9_remove_compressor(VP9_COMP *cpi) {
 #if CONFIG_INTERNAL_STATS
     vp9_clear_system_state();
 
-    // printf("\n8x8-4x4:%d-%d\n", cpi->t8x8_count, cpi->t4x4_count);
     if (cpi->oxcf.pass != 1) {
+      char headings[512] = {0};
+      char results[512] = {0};
       FILE *f = fopen("opsnr.stt", "a");
       double time_encoded = (cpi->last_end_time_stamp_seen
                              - cpi->first_time_stamp_ever) / 10000000.000;
@@ -1897,39 +1909,39 @@ void vp9_remove_compressor(VP9_COMP *cpi) {
             vpx_sse_to_psnr((double)cpi->totalp_samples, peak,
                             (double)cpi->totalp_sq_error);
         const double total_ssim = 100 * pow(cpi->summed_quality /
-                                                cpi->summed_weights, 8.0);
+                                            cpi->summed_weights, 8.0);
+
+        snprintf(headings, sizeof(headings),
+                 "Bitrate\tAVGPsnr\tGLBPsnr\tAVPsnrP\tGLPsnrP\t"
+                 "VPXSSIM\tFASTSIM\tPSNRHVS");
+        snprintf(results, sizeof(results),
+                 "%7.2f\t%7.3f\t%7.3f\t%7.3f\t%7.3f\t"
+                 "%7.3f\t%7.3f\t%7.3f", dr,
+                 cpi->total / cpi->count, total_psnr,
+                 cpi->totalp / cpi->count, totalp_psnr, total_ssim,
+                 cpi->total_fastssim_all / cpi->count,
+                 cpi->total_psnrhvs_all / cpi->count);
         if (cpi->b_calculate_blockiness) {
-          fprintf(f, "Bitrate\tAVGPsnr\tGLBPsnr\tAVPsnrP\tGLPsnrP\t"
-                "VPXSSIM\tVPSSIMP\tFASTSSIM\tPSNRHVS\tTime(ms)\n");
-          fprintf(f, "%7.2f\t%7.3f\t%7.3f\t%7.3f\t%7.3f\t%7.3f\t"
-                "%7.3f\t%7.3f\t%8.0f\n",
-                  dr, cpi->total / cpi->count, total_psnr,
-                  cpi->totalp / cpi->count, totalp_psnr, total_ssim,
-                cpi->total_fastssim_all / cpi->count,
-                cpi->total_psnrhvs_all / cpi->count,
-                total_encode_time);
-        } else {
-          fprintf(f, "Bitrate\tAVGPsnr\tGLBPsnr\tAVPsnrP\tGLPsnrP\t"
-                "VPXSSIM\tVPSSIMP\tBlockiness\tFASTSSIM\tPSNRHVS\tTime(ms)\n");
-          fprintf(f, "%7.2f\t%7.3f\t%7.3f\t%7.3f\t%7.3f\t%7.3f\t"
-                  "%7.3f\t%7.3f\t%7.3f\t%8.0f\n",
-                  dr, cpi->total / cpi->count, total_psnr,
-                  cpi->totalp / cpi->count, totalp_psnr, total_ssim,
-                  cpi->total_blockiness / cpi->count,
-                  cpi->total_fastssim_all / cpi->count,
-                  cpi->total_psnrhvs_all / cpi->count,
-                  total_encode_time);
+          SNPRINT(headings, "\t  Block");
+          SNPRINT2(results, "\t%7.3f", cpi->total_blockiness / cpi->count);
         }
-      }
 
+        if (cpi->b_calculate_consistency) {
+          double consistency =
+              vpx_sse_to_psnr((double)cpi->totalp_samples, peak,
+                              (double)cpi->total_inconsistency);
 
-      if (cpi->b_calculate_ssimg) {
-        fprintf(f, "BitRate\tSSIM_Y\tSSIM_U\tSSIM_V\tSSIM_A\t  Time(ms)\n");
-        fprintf(f, "%7.2f\t%6.4f\t%6.4f\t%6.4f\t%6.4f\t%8.0f\n", dr,
-                cpi->total_ssimg_y / cpi->count,
-                cpi->total_ssimg_u / cpi->count,
-                cpi->total_ssimg_v / cpi->count,
-                cpi->total_ssimg_all / cpi->count, total_encode_time);
+          SNPRINT(headings, "\tConsist");
+          SNPRINT2(results, "\t%7.3f", consistency);
+        }
+
+        if (cpi->b_calculate_ssimg) {
+          SNPRINT(headings, "\t  SSIMG");
+          SNPRINT2(results, "\t%7.3f", cpi->total_ssimg_all / cpi->count);
+        }
+
+        fprintf(f, "%s\t    Time\n", headings);
+        fprintf(f, "%s\t%8.0f\n", results, total_encode_time);
       }
 
       fclose(f);
@@ -4201,6 +4213,16 @@ int vp9_get_compressed_data(VP9_COMP *cpi, unsigned int *frame_flags,
                                cm->frame_to_show->y_stride,
                                cpi->Source->y_width, cpi->Source->y_height);
 
+      if (cpi->b_calculate_consistency)
+        cpi->total_inconsistency += vp9_get_ssim_metrics(cpi->Source->y_buffer,
+                                                   cpi->Source->y_stride,
+                                                   cm->frame_to_show->y_buffer,
+                                                   cm->frame_to_show->y_stride,
+                                                   cpi->Source->y_width,
+                                                   cpi->Source->y_height,
+                                                   cpi->ssim_vars,
+                                                   &cpi->metrics, 1);
+
       if (cpi->b_calculate_ssimg) {
         double y, u, v, frame_all;
 #if CONFIG_VP9_HIGHBITDEPTH

vp9/encoder/vp9_encoder.h

@@ -34,6 +34,9 @@
 #include "vp9/encoder/vp9_quantize.h"
 #include "vp9/encoder/vp9_ratectrl.h"
 #include "vp9/encoder/vp9_rd.h"
+#if CONFIG_INTERNAL_STATS
+#include "vp9/encoder/vp9_ssim.h"
+#endif
 #include "vp9/encoder/vp9_speed_features.h"
 #include "vp9/encoder/vp9_svc_layercontext.h"
 #include "vp9/encoder/vp9_tokenize.h"
@@ -429,6 +432,10 @@ typedef struct VP9_COMP {
 
   int b_calculate_ssimg;
   int b_calculate_blockiness;
+  int b_calculate_consistency;
+  double total_inconsistency;
+  Ssimv *ssim_vars;
+  Metrics metrics;
 #endif
   int b_calculate_psnr;
 

vp9/encoder/vp9_ssim.c

@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <math.h>
 #include "./vp9_rtcd.h"
-
 #include "vp9/encoder/vp9_ssim.h"
 
 void vp9_ssim_parms_16x16_c(uint8_t *s, int sp, uint8_t *r,
@@ -201,6 +201,251 @@ double vp9_calc_ssimg(YV12_BUFFER_CONFIG *source, YV12_BUFFER_CONFIG *dest,
   return ssim_all;
 }
 
+// traditional ssim as per: http://en.wikipedia.org/wiki/Structural_similarity
+//
+// Re working out the math ->
+//
+// ssim(x,y) =  (2*mean(x)*mean(y) + c1)*(2*cov(x,y)+c2) /
+//   ((mean(x)^2+mean(y)^2+c1)*(var(x)+var(y)+c2))
+//
+// mean(x) = sum(x) / n
+//
+// cov(x,y) = (n*sum(xi*yi)-sum(x)*sum(y))/(n*n)
+//
+// var(x) = (n*sum(xi*xi)-sum(xi)*sum(xi))/(n*n)
+//
+// ssim(x,y) =
+//   (2*sum(x)*sum(y)/(n*n) + c1)*(2*(n*sum(xi*yi)-sum(x)*sum(y))/(n*n)+c2) /
+//   (((sum(x)*sum(x)+sum(y)*sum(y))/(n*n) +c1) *
+//    ((n*sum(xi*xi) - sum(xi)*sum(xi))/(n*n)+
+//     (n*sum(yi*yi) - sum(yi)*sum(yi))/(n*n)+c2)))
+//
+// factoring out n*n
+//
+// ssim(x,y) =
+//   (2*sum(x)*sum(y) + n*n*c1)*(2*(n*sum(xi*yi)-sum(x)*sum(y))+n*n*c2) /
+//   (((sum(x)*sum(x)+sum(y)*sum(y)) + n*n*c1) *
+//    (n*sum(xi*xi)-sum(xi)*sum(xi)+n*sum(yi*yi)-sum(yi)*sum(yi)+n*n*c2))
+//
+// Replace c1 with n*n * c1 for the final step that leads to this code:
+// The final step scales by 12 bits so we don't lose precision in the constants.
+
+double ssimv_similarity(Ssimv *sv, int64_t n) {
+  // Scale the constants by number of pixels.
+  const int64_t c1 = (cc1 * n * n) >> 12;
+  const int64_t c2 = (cc2 * n * n) >> 12;
+
+  const double l = 1.0 * (2 * sv->sum_s * sv->sum_r + c1) /
+      (sv->sum_s * sv->sum_s + sv->sum_r * sv->sum_r + c1);
+
+  // Since these variables are unsigned sums, convert to double so
+  // math is done in double arithmetic.
+  const double v = (2.0 * n * sv->sum_sxr - 2 * sv->sum_s * sv->sum_r + c2)
+      / (n * sv->sum_sq_s - sv->sum_s * sv->sum_s + n * sv->sum_sq_r
+         - sv->sum_r * sv->sum_r + c2);
+
+  return l * v;
+}
+
+// The first term of the ssim metric is a luminance factor.
+//
+// (2*mean(x)*mean(y) + c1)/ (mean(x)^2+mean(y)^2+c1)
+//
+// This luminance factor is super sensitive to the dark side of luminance
+// values and completely insensitive on the white side.  check out 2 sets
+// (1,3) and (250,252) the term gives ( 2*1*3/(1+9) = .60
+// 2*250*252/ (250^2+252^2) => .99999997
+//
+// As a result in this tweaked version of the calculation in which the
+// luminance is taken as percentage off from peak possible.
+//
+// 255 * 255 - (sum_s - sum_r) / count * (sum_s - sum_r) / count
+//
+double ssimv_similarity2(Ssimv *sv, int64_t n) {
+  // Scale the constants by number of pixels.
+  const int64_t c1 = (cc1 * n * n) >> 12;
+  const int64_t c2 = (cc2 * n * n) >> 12;
+
+  const double mean_diff = (1.0 * sv->sum_s - sv->sum_r) / n;
+  const double l = (255 * 255 - mean_diff * mean_diff + c1) / (255 * 255 + c1);
+
+  // Since these variables are unsigned, sums convert to double so
+  // math is done in double arithmetic.
+  const double v = (2.0 * n * sv->sum_sxr - 2 * sv->sum_s * sv->sum_r + c2)
+      / (n * sv->sum_sq_s - sv->sum_s * sv->sum_s +
+         n * sv->sum_sq_r - sv->sum_r * sv->sum_r + c2);
+
+  return l * v;
+}
+void ssimv_parms(uint8_t *img1, int img1_pitch, uint8_t *img2, int img2_pitch,
+                 Ssimv *sv) {
+  vp9_ssim_parms_8x8(img1, img1_pitch, img2, img2_pitch,
+                     &sv->sum_s, &sv->sum_r, &sv->sum_sq_s, &sv->sum_sq_r,
+                     &sv->sum_sxr);
+}
+
+double vp9_get_ssim_metrics(uint8_t *img1, int img1_pitch,
+                            uint8_t *img2, int img2_pitch,
+                            int width, int height,
+                            Ssimv *sv2, Metrics *m,
+                            int do_inconsistency) {
+  double dssim_total = 0;
+  double ssim_total = 0;
+  double ssim2_total = 0;
+  double inconsistency_total = 0;
+  int i, j;
+  int c = 0;
+  double norm;
+  double old_ssim_total = 0;
+  vp9_clear_system_state();
+  // We can sample points as frequently as we like start with 1 per 4x4.
+  for (i = 0; i < height; i += 4,
+       img1 += img1_pitch * 4, img2 += img2_pitch * 4) {
+    for (j = 0; j < width; j += 4, ++c) {
+      Ssimv sv = {0};
+      double ssim;
+      double ssim2;
+      double dssim;
+      uint32_t var_new;
+      uint32_t var_old;
+      uint32_t mean_new;
+      uint32_t mean_old;
+      double ssim_new;
+      double ssim_old;
+
+      // Not sure there's a great way to handle the edge pixels
+      // in ssim when using a window. Seems biased against edge pixels
+      // however you handle this. This uses only samples that are
+      // fully in the frame.
+      if (j + 8 <= width && i + 8 <= height) {
+        ssimv_parms(img1 + j, img1_pitch, img2 + j, img2_pitch, &sv);
+      }
+
+      ssim = ssimv_similarity(&sv, 64);
+      ssim2 = ssimv_similarity2(&sv, 64);
+
+      sv.ssim = ssim2;
+
+      // dssim is calculated to use as an actual error metric and
+      // is scaled up to the same range as sum square error.
+      // Since we are subsampling every 16th point maybe this should be
+      // *16 ?
+      dssim = 255 * 255 * (1 - ssim2) / 2;
+
+      // Here I introduce a new error metric: consistency-weighted
+      // SSIM-inconsistency.  This metric isolates frames where the
+      // SSIM 'suddenly' changes, e.g. if one frame in every 8 is much
+      // sharper or blurrier than the others. Higher values indicate a
+      // temporally inconsistent SSIM. There are two ideas at work:
+      //
+      // 1) 'SSIM-inconsistency': the total inconsistency value
+      // reflects how much SSIM values are changing between this
+      // source / reference frame pair and the previous pair.
+      //
+      // 2) 'consistency-weighted': weights de-emphasize areas in the
+      // frame where the scene content has changed. Changes in scene
+      // content are detected via changes in local variance and local
+      // mean.
+      //
+      // Thus the overall measure reflects how inconsistent the SSIM
+      // values are, over consistent regions of the frame.
+      //
+      // The metric has three terms:
+      //
+      // term 1 -> uses change in scene Variance to weight error score
+      //  2 * var(Fi)*var(Fi-1) / (var(Fi)^2+var(Fi-1)^2)
+      //  larger changes from one frame to the next mean we care
+      //  less about consistency.
+      //
+      // term 2 -> uses change in local scene luminance to weight error
+      //  2 * avg(Fi)*avg(Fi-1) / (avg(Fi)^2+avg(Fi-1)^2)
+      //  larger changes from one frame to the next mean we care
+      //  less about consistency.
+      //
+      // term3 -> measures inconsistency in ssim scores between frames
+      //   1 - ( 2 * ssim(Fi)*ssim(Fi-1)/(ssim(Fi)^2+sssim(Fi-1)^2).
+      //
+      // This term compares the ssim score for the same location in 2
+      // subsequent frames.
+      var_new = sv.sum_sq_s - sv.sum_s * sv.sum_s / 64;
+      var_old = sv2[c].sum_sq_s - sv2[c].sum_s * sv2[c].sum_s / 64;
+      mean_new = sv.sum_s;
+      mean_old = sv2[c].sum_s;
+      ssim_new = sv.ssim;
+      ssim_old = sv2[c].ssim;
+
+      if (do_inconsistency) {
+        // We do the metric once for every 4x4 block in the image. Since
+        // we are scaling the error to SSE for use in a psnr calculation
+        // 1.0 = 4x4x255x255 the worst error we can possibly have.
+        static const double kScaling = 4. * 4 * 255 * 255;
+
+        // The constants have to be non 0 to avoid potential divide by 0
+        // issues other than that they affect kind of a weighting between
+        // the terms.  No testing of what the right terms should be has been
+        // done.
+        static const double c1 = 1, c2 = 1, c3 = 1;
+
+        // This measures how much consistent variance is in two consecutive
+        // source frames. 1.0 means they have exactly the same variance.
+        const double variance_term = (2.0 * var_old * var_new + c1) /
+            (1.0 * var_old * var_old + 1.0 * var_new * var_new + c1);
+
+        // This measures how consistent the local mean are between two
+        // consecutive frames. 1.0 means they have exactly the same mean.
+        const double mean_term = (2.0 * mean_old * mean_new + c2) /
+            (1.0 * mean_old * mean_old + 1.0 * mean_new * mean_new + c2);
+
+        // This measures how consistent the ssims of two
+        // consecutive frames is. 1.0 means they are exactly the same.
+        double ssim_term = pow((2.0 * ssim_old * ssim_new + c3) /
+                               (ssim_old * ssim_old + ssim_new * ssim_new + c3),
+                               5);
+
+        double this_inconsistency;
+
+        // Floating point math sometimes makes this > 1 by a tiny bit.
+        // We want the metric to scale between 0 and 1.0 so we can convert
+        // it to an snr scaled value.
+        if (ssim_term > 1)
+          ssim_term = 1;
+
+        // This converts the consistency metric to an inconsistency metric
+        // ( so we can scale it like psnr to something like sum square error.