webp/src/enc/filter.c - nest-cam/4320010/webp - Git at Google

 // Copyright 2011 Google Inc. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the COPYING 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.
 // -----------------------------------------------------------------------------
 //
 // Selecting filter level
 //
 // Author: somnath@google.com (Somnath Banerjee)

 #include <assert.h>
 #include "./vp8enci.h"
 #include "../dsp/dsp.h"

 // This table gives, for a given sharpness, the filtering strength to be
 // used (at least) in order to filter a given edge step delta.
 // This is constructed by brute force inspection: for all delta, we iterate
 // over all possible filtering strength / thresh until needs_filter() returns
 // true.
 #define MAX_DELTA_SIZE 64
 static const uint8_t kLevelsFromDelta[8][MAX_DELTA_SIZE] = {
   { 0,   1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
     16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
     32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
     48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63 },
   { 0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 13, 14, 15, 17, 18,
     20, 21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42,
     44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
   {  0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 13, 14, 16, 17, 19,
     20, 22, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43,
     44, 46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
   {  0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 13, 15, 16, 18, 19,
     21, 22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43,
     45, 46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 61, 63, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
   {  0,  1,  2,  3,  5,  6,  7,  8,  9, 11, 12, 14, 15, 17, 18, 20,
     21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44,
     45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
   {  0,  1,  2,  4,  5,  7,  8,  9, 11, 12, 13, 15, 16, 17, 19, 20,
     22, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43, 44,
     46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 63, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
   {  0,  1,  2,  4,  5,  7,  8,  9, 11, 12, 13, 15, 16, 18, 19, 21,
     22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43, 45,
     46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 61, 63, 63, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
   {  0,  1,  2,  4,  5,  7,  8,  9, 11, 12, 14, 15, 17, 18, 20, 21,
     23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44, 45,
     47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63, 63, 63,
     63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 }
 };

 int VP8FilterStrengthFromDelta(int sharpness, int delta) {
   const int pos = (delta < MAX_DELTA_SIZE) ? delta : MAX_DELTA_SIZE - 1;
   assert(sharpness >= 0 && sharpness <= 7);
   return kLevelsFromDelta[sharpness][pos];
 }

 //------------------------------------------------------------------------------
 // Paragraph 15.4: compute the inner-edge filtering strength

 static int GetILevel(int sharpness, int level) {
   if (sharpness > 0) {
     if (sharpness > 4) {
       level >>= 2;
     } else {
       level >>= 1;
     }
     if (level > 9 - sharpness) {
       level = 9 - sharpness;
     }
   }
   if (level < 1) level = 1;
   return level;
 }

 static void DoFilter(const VP8EncIterator* const it, int level) {
   const VP8Encoder* const enc = it->enc_;
   const int ilevel = GetILevel(enc->config_->filter_sharpness, level);
   const int limit = 2 * level + ilevel;

   uint8_t* const y_dst = it->yuv_out2_ + Y_OFF;
   uint8_t* const u_dst = it->yuv_out2_ + U_OFF;
   uint8_t* const v_dst = it->yuv_out2_ + V_OFF;

   // copy current block to yuv_out2_
   memcpy(y_dst, it->yuv_out_, YUV_SIZE * sizeof(uint8_t));

   if (enc->filter_hdr_.simple_ == 1) {   // simple
     VP8SimpleHFilter16i(y_dst, BPS, limit);
     VP8SimpleVFilter16i(y_dst, BPS, limit);
   } else {    // complex
     const int hev_thresh = (level >= 40) ? 2 : (level >= 15) ? 1 : 0;
     VP8HFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
     VP8HFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
     VP8VFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
     VP8VFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
   }
 }

 //------------------------------------------------------------------------------
 // SSIM metric

 enum { KERNEL = 3 };
 static const double kMinValue = 1.e-10;  // minimal threshold

 void VP8SSIMAddStats(const DistoStats* const src, DistoStats* const dst) {
   dst->w   += src->w;
   dst->xm  += src->xm;
   dst->ym  += src->ym;
   dst->xxm += src->xxm;
   dst->xym += src->xym;
   dst->yym += src->yym;
 }

 static void VP8SSIMAccumulate(const uint8_t* src1, int stride1,
                               const uint8_t* src2, int stride2,
                               int xo, int yo, int W, int H,
                               DistoStats* const stats) {
   const int ymin = (yo - KERNEL < 0) ? 0 : yo - KERNEL;
   const int ymax = (yo + KERNEL > H - 1) ? H - 1 : yo + KERNEL;
   const int xmin = (xo - KERNEL < 0) ? 0 : xo - KERNEL;
   const int xmax = (xo + KERNEL > W - 1) ? W - 1 : xo + KERNEL;
   int x, y;
   src1 += ymin * stride1;
   src2 += ymin * stride2;
   for (y = ymin; y <= ymax; ++y, src1 += stride1, src2 += stride2) {
     for (x = xmin; x <= xmax; ++x) {
       const int s1 = src1[x];
       const int s2 = src2[x];
       stats->w   += 1;
       stats->xm  += s1;
       stats->ym  += s2;
       stats->xxm += s1 * s1;
       stats->xym += s1 * s2;
       stats->yym += s2 * s2;
     }
   }
 }

 double VP8SSIMGet(const DistoStats* const stats) {
   const double xmxm = stats->xm * stats->xm;
   const double ymym = stats->ym * stats->ym;
   const double xmym = stats->xm * stats->ym;
   const double w2 = stats->w * stats->w;
   double sxx = stats->xxm * stats->w - xmxm;
   double syy = stats->yym * stats->w - ymym;
   double sxy = stats->xym * stats->w - xmym;
   double C1, C2;
   double fnum;
   double fden;
   // small errors are possible, due to rounding. Clamp to zero.
   if (sxx < 0.) sxx = 0.;
   if (syy < 0.) syy = 0.;
   C1 = 6.5025 * w2;
   C2 = 58.5225 * w2;
   fnum = (2 * xmym + C1) * (2 * sxy + C2);
   fden = (xmxm + ymym + C1) * (sxx + syy + C2);
   return (fden != 0.) ? fnum / fden : kMinValue;
 }

 double VP8SSIMGetSquaredError(const DistoStats* const s) {
   if (s->w > 0.) {
     const double iw2 = 1. / (s->w * s->w);
     const double sxx = s->xxm * s->w - s->xm * s->xm;
     const double syy = s->yym * s->w - s->ym * s->ym;
     const double sxy = s->xym * s->w - s->xm * s->ym;
     const double SSE = iw2 * (sxx + syy - 2. * sxy);
     if (SSE > kMinValue) return SSE;
   }
   return kMinValue;
 }

 void VP8SSIMAccumulatePlane(const uint8_t* src1, int stride1,
                             const uint8_t* src2, int stride2,
                             int W, int H, DistoStats* const stats) {
   int x, y;
   for (y = 0; y < H; ++y) {
     for (x = 0; x < W; ++x) {
       VP8SSIMAccumulate(src1, stride1, src2, stride2, x, y, W, H, stats);
     }
   }
 }

 static double GetMBSSIM(const uint8_t* yuv1, const uint8_t* yuv2) {
   int x, y;
   DistoStats s = { .0, .0, .0, .0, .0, .0 };

   // compute SSIM in a 10 x 10 window
   for (x = 3; x < 13; x++) {
     for (y = 3; y < 13; y++) {
       VP8SSIMAccumulate(yuv1 + Y_OFF, BPS, yuv2 + Y_OFF, BPS, x, y, 16, 16, &s);
     }
   }
   for (x = 1; x < 7; x++) {
     for (y = 1; y < 7; y++) {
       VP8SSIMAccumulate(yuv1 + U_OFF, BPS, yuv2 + U_OFF, BPS, x, y, 8, 8, &s);
       VP8SSIMAccumulate(yuv1 + V_OFF, BPS, yuv2 + V_OFF, BPS, x, y, 8, 8, &s);
     }
   }
   return VP8SSIMGet(&s);
 }

 //------------------------------------------------------------------------------
 // Exposed APIs: Encoder should call the following 3 functions to adjust
 // loop filter strength

 void VP8InitFilter(VP8EncIterator* const it) {
   if (it->lf_stats_ != NULL) {
     int s, i;
     for (s = 0; s < NUM_MB_SEGMENTS; s++) {
       for (i = 0; i < MAX_LF_LEVELS; i++) {
         (*it->lf_stats_)[s][i] = 0;
       }
     }
   }
 }

 void VP8StoreFilterStats(VP8EncIterator* const it) {
   int d;
   VP8Encoder* const enc = it->enc_;
   const int s = it->mb_->segment_;
   const int level0 = enc->dqm_[s].fstrength_;  // TODO: ref_lf_delta[]

   // explore +/-quant range of values around level0
   const int delta_min = -enc->dqm_[s].quant_;
   const int delta_max = enc->dqm_[s].quant_;
   const int step_size = (delta_max - delta_min >= 4) ? 4 : 1;

   if (it->lf_stats_ == NULL) return;

   // NOTE: Currently we are applying filter only across the sublock edges
   // There are two reasons for that.
   // 1. Applying filter on macro block edges will change the pixels in
   // the left and top macro blocks. That will be hard to restore
   // 2. Macro Blocks on the bottom and right are not yet compressed. So we
   // cannot apply filter on the right and bottom macro block edges.
   if (it->mb_->type_ == 1 && it->mb_->skip_) return;

   // Always try filter level  zero
   (*it->lf_stats_)[s][0] += GetMBSSIM(it->yuv_in_, it->yuv_out_);

   for (d = delta_min; d <= delta_max; d += step_size) {
     const int level = level0 + d;
     if (level <= 0 || level >= MAX_LF_LEVELS) {
       continue;
     }
     DoFilter(it, level);
     (*it->lf_stats_)[s][level] += GetMBSSIM(it->yuv_in_, it->yuv_out2_);
   }
 }

 void VP8AdjustFilterStrength(VP8EncIterator* const it) {
   VP8Encoder* const enc = it->enc_;
   if (it->lf_stats_ != NULL) {
     int s;
     for (s = 0; s < NUM_MB_SEGMENTS; s++) {
       int i, best_level = 0;
       // Improvement over filter level 0 should be at least 1e-5 (relatively)
       double best_v = 1.00001 * (*it->lf_stats_)[s][0];
       for (i = 1; i < MAX_LF_LEVELS; i++) {
         const double v = (*it->lf_stats_)[s][i];
         if (v > best_v) {
           best_v = v;
           best_level = i;
         }
       }
       enc->dqm_[s].fstrength_ = best_level;
     }
   } else if (enc->config_->filter_strength > 0) {
     int max_level = 0;
     int s;
     for (s = 0; s < NUM_MB_SEGMENTS; s++) {
       VP8SegmentInfo* const dqm = &enc->dqm_[s];
       // this '>> 3' accounts for some inverse WHT scaling
       const int delta = (dqm->max_edge_ * dqm->y2_.q_[1]) >> 3;
       const int level =
           VP8FilterStrengthFromDelta(enc->filter_hdr_.sharpness_, delta);
       if (level > dqm->fstrength_) {
         dqm->fstrength_ = level;
       }
       if (max_level < dqm->fstrength_) {
         max_level = dqm->fstrength_;
       }
     }
     enc->filter_hdr_.level_ = max_level;
   }
 }

 // -----------------------------------------------------------------------------
	// Copyright 2011 Google Inc. All Rights Reserved.
	//
	// Use of this source code is governed by a BSD-style license
	// that can be found in the COPYING 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.
	// -----------------------------------------------------------------------------
	//
	// Selecting filter level
	//
	// Author: somnath@google.com (Somnath Banerjee)

	#include <assert.h>
	#include "./vp8enci.h"
	#include "../dsp/dsp.h"

	// This table gives, for a given sharpness, the filtering strength to be
	// used (at least) in order to filter a given edge step delta.
	// This is constructed by brute force inspection: for all delta, we iterate
	// over all possible filtering strength / thresh until needs_filter() returns
	// true.
	#define MAX_DELTA_SIZE 64
	static const uint8_t kLevelsFromDelta[8][MAX_DELTA_SIZE] = {
	{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
	16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
	32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
	48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63 },
	{ 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 17, 18,
	20, 21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42,
	44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
	{ 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 19,
	20, 22, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43,
	44, 46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
	{ 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13, 15, 16, 18, 19,
	21, 22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43,
	45, 46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 61, 63, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
	{ 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 14, 15, 17, 18, 20,
	21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44,
	45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
	{ 0, 1, 2, 4, 5, 7, 8, 9, 11, 12, 13, 15, 16, 17, 19, 20,
	22, 23, 25, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43, 44,
	46, 47, 49, 50, 52, 53, 55, 56, 58, 59, 61, 62, 63, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
	{ 0, 1, 2, 4, 5, 7, 8, 9, 11, 12, 13, 15, 16, 18, 19, 21,
	22, 24, 25, 27, 28, 30, 31, 33, 34, 36, 37, 39, 40, 42, 43, 45,
	46, 48, 49, 51, 52, 54, 55, 57, 58, 60, 61, 63, 63, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 },
	{ 0, 1, 2, 4, 5, 7, 8, 9, 11, 12, 14, 15, 17, 18, 20, 21,
	23, 24, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44, 45,
	47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 63, 63, 63, 63,
	63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63 }
	};

	int VP8FilterStrengthFromDelta(int sharpness, int delta) {
	const int pos = (delta < MAX_DELTA_SIZE) ? delta : MAX_DELTA_SIZE - 1;
	assert(sharpness >= 0 && sharpness <= 7);
	return kLevelsFromDelta[sharpness][pos];
	}

	//------------------------------------------------------------------------------
	// Paragraph 15.4: compute the inner-edge filtering strength

	static int GetILevel(int sharpness, int level) {
	if (sharpness > 0) {
	if (sharpness > 4) {
	level >>= 2;
	} else {
	level >>= 1;
	}
	if (level > 9 - sharpness) {
	level = 9 - sharpness;
	}
	}
	if (level < 1) level = 1;
	return level;
	}

	static void DoFilter(const VP8EncIterator* const it, int level) {
	const VP8Encoder* const enc = it->enc_;
	const int ilevel = GetILevel(enc->config_->filter_sharpness, level);
	const int limit = 2 * level + ilevel;

	uint8_t* const y_dst = it->yuv_out2_ + Y_OFF;
	uint8_t* const u_dst = it->yuv_out2_ + U_OFF;
	uint8_t* const v_dst = it->yuv_out2_ + V_OFF;

	// copy current block to yuv_out2_
	memcpy(y_dst, it->yuv_out_, YUV_SIZE * sizeof(uint8_t));

	if (enc->filter_hdr_.simple_ == 1) { // simple
	VP8SimpleHFilter16i(y_dst, BPS, limit);
	VP8SimpleVFilter16i(y_dst, BPS, limit);
	} else { // complex
	const int hev_thresh = (level >= 40) ? 2 : (level >= 15) ? 1 : 0;
	VP8HFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
	VP8HFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
	VP8VFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
	VP8VFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
	}
	}

	//------------------------------------------------------------------------------
	// SSIM metric

	enum { KERNEL = 3 };
	static const double kMinValue = 1.e-10; // minimal threshold

	void VP8SSIMAddStats(const DistoStats* const src, DistoStats* const dst) {
	dst->w += src->w;
	dst->xm += src->xm;
	dst->ym += src->ym;
	dst->xxm += src->xxm;
	dst->xym += src->xym;
	dst->yym += src->yym;
	}

	static void VP8SSIMAccumulate(const uint8_t* src1, int stride1,
	const uint8_t* src2, int stride2,
	int xo, int yo, int W, int H,
	DistoStats* const stats) {
	const int ymin = (yo - KERNEL < 0) ? 0 : yo - KERNEL;
	const int ymax = (yo + KERNEL > H - 1) ? H - 1 : yo + KERNEL;
	const int xmin = (xo - KERNEL < 0) ? 0 : xo - KERNEL;
	const int xmax = (xo + KERNEL > W - 1) ? W - 1 : xo + KERNEL;
	int x, y;
	src1 += ymin * stride1;
	src2 += ymin * stride2;
	for (y = ymin; y <= ymax; ++y, src1 += stride1, src2 += stride2) {
	for (x = xmin; x <= xmax; ++x) {
	const int s1 = src1[x];
	const int s2 = src2[x];
	stats->w += 1;
	stats->xm += s1;
	stats->ym += s2;
	stats->xxm += s1 * s1;
	stats->xym += s1 * s2;
	stats->yym += s2 * s2;
	}
	}
	}

	double VP8SSIMGet(const DistoStats* const stats) {
	const double xmxm = stats->xm * stats->xm;
	const double ymym = stats->ym * stats->ym;
	const double xmym = stats->xm * stats->ym;
	const double w2 = stats->w * stats->w;
	double sxx = stats->xxm * stats->w - xmxm;
	double syy = stats->yym * stats->w - ymym;
	double sxy = stats->xym * stats->w - xmym;
	double C1, C2;
	double fnum;
	double fden;
	// small errors are possible, due to rounding. Clamp to zero.
	if (sxx < 0.) sxx = 0.;
	if (syy < 0.) syy = 0.;
	C1 = 6.5025 * w2;
	C2 = 58.5225 * w2;
	fnum = (2 * xmym + C1) * (2 * sxy + C2);
	fden = (xmxm + ymym + C1) * (sxx + syy + C2);
	return (fden != 0.) ? fnum / fden : kMinValue;
	}

	double VP8SSIMGetSquaredError(const DistoStats* const s) {
	if (s->w > 0.) {
	const double iw2 = 1. / (s->w * s->w);
	const double sxx = s->xxm * s->w - s->xm * s->xm;
	const double syy = s->yym * s->w - s->ym * s->ym;
	const double sxy = s->xym * s->w - s->xm * s->ym;
	const double SSE = iw2 * (sxx + syy - 2. * sxy);
	if (SSE > kMinValue) return SSE;
	}
	return kMinValue;
	}

	void VP8SSIMAccumulatePlane(const uint8_t* src1, int stride1,
	const uint8_t* src2, int stride2,
	int W, int H, DistoStats* const stats) {
	int x, y;
	for (y = 0; y < H; ++y) {
	for (x = 0; x < W; ++x) {
	VP8SSIMAccumulate(src1, stride1, src2, stride2, x, y, W, H, stats);
	}
	}
	}

	static double GetMBSSIM(const uint8_t* yuv1, const uint8_t* yuv2) {
	int x, y;
	DistoStats s = { .0, .0, .0, .0, .0, .0 };

	// compute SSIM in a 10 x 10 window
	for (x = 3; x < 13; x++) {
	for (y = 3; y < 13; y++) {
	VP8SSIMAccumulate(yuv1 + Y_OFF, BPS, yuv2 + Y_OFF, BPS, x, y, 16, 16, &s);
	}
	}
	for (x = 1; x < 7; x++) {
	for (y = 1; y < 7; y++) {
	VP8SSIMAccumulate(yuv1 + U_OFF, BPS, yuv2 + U_OFF, BPS, x, y, 8, 8, &s);
	VP8SSIMAccumulate(yuv1 + V_OFF, BPS, yuv2 + V_OFF, BPS, x, y, 8, 8, &s);
	}
	}
	return VP8SSIMGet(&s);
	}

	//------------------------------------------------------------------------------
	// Exposed APIs: Encoder should call the following 3 functions to adjust
	// loop filter strength

	void VP8InitFilter(VP8EncIterator* const it) {
	if (it->lf_stats_ != NULL) {
	int s, i;
	for (s = 0; s < NUM_MB_SEGMENTS; s++) {
	for (i = 0; i < MAX_LF_LEVELS; i++) {
	(*it->lf_stats_)[s][i] = 0;
	}
	}
	}
	}

	void VP8StoreFilterStats(VP8EncIterator* const it) {
	int d;
	VP8Encoder* const enc = it->enc_;
	const int s = it->mb_->segment_;
	const int level0 = enc->dqm_[s].fstrength_; // TODO: ref_lf_delta[]

	// explore +/-quant range of values around level0
	const int delta_min = -enc->dqm_[s].quant_;
	const int delta_max = enc->dqm_[s].quant_;
	const int step_size = (delta_max - delta_min >= 4) ? 4 : 1;

	if (it->lf_stats_ == NULL) return;

	// NOTE: Currently we are applying filter only across the sublock edges
	// There are two reasons for that.
	// 1. Applying filter on macro block edges will change the pixels in
	// the left and top macro blocks. That will be hard to restore
	// 2. Macro Blocks on the bottom and right are not yet compressed. So we
	// cannot apply filter on the right and bottom macro block edges.
	if (it->mb_->type_ == 1 && it->mb_->skip_) return;

	// Always try filter level zero
	(*it->lf_stats_)[s][0] += GetMBSSIM(it->yuv_in_, it->yuv_out_);

	for (d = delta_min; d <= delta_max; d += step_size) {
	const int level = level0 + d;
	if (level <= 0 \|\| level >= MAX_LF_LEVELS) {
	continue;
	}
	DoFilter(it, level);
	(*it->lf_stats_)[s][level] += GetMBSSIM(it->yuv_in_, it->yuv_out2_);
	}
	}

	void VP8AdjustFilterStrength(VP8EncIterator* const it) {
	VP8Encoder* const enc = it->enc_;
	if (it->lf_stats_ != NULL) {
	int s;
	for (s = 0; s < NUM_MB_SEGMENTS; s++) {
	int i, best_level = 0;
	// Improvement over filter level 0 should be at least 1e-5 (relatively)
	double best_v = 1.00001 * (*it->lf_stats_)[s][0];
	for (i = 1; i < MAX_LF_LEVELS; i++) {
	const double v = (*it->lf_stats_)[s][i];
	if (v > best_v) {
	best_v = v;
	best_level = i;
	}
	}
	enc->dqm_[s].fstrength_ = best_level;
	}
	} else if (enc->config_->filter_strength > 0) {
	int max_level = 0;
	int s;
	for (s = 0; s < NUM_MB_SEGMENTS; s++) {
	VP8SegmentInfo* const dqm = &enc->dqm_[s];
	// this '>> 3' accounts for some inverse WHT scaling
	const int delta = (dqm->max_edge_ * dqm->y2_.q_[1]) >> 3;
	const int level =
	VP8FilterStrengthFromDelta(enc->filter_hdr_.sharpness_, delta);
	if (level > dqm->fstrength_) {
	dqm->fstrength_ = level;
	}
	if (max_level < dqm->fstrength_) {
	max_level = dqm->fstrength_;
	}
	}
	enc->filter_hdr_.level_ = max_level;
	}
	}

	// -----------------------------------------------------------------------------