text: /*
   *  Copyright (c) 2014 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 <stdlib.h>
  
  #include "vpx/vpx_integer.h"
  #include "vpx_ports/system_state.h"
  
  static int horizontal_filter(const uint8_t *s) {
    return (s[1] - s[-2]) * 2 + (s[-1] - s[0]) * 6;
  }
  
  static int vertical_filter(const uint8_t *s, int p) {
    return (s[p] - s[-2 * p]) * 2 + (s[-p] - s[0]) * 6;
  }
  
  static int variance(int sum, int sum_squared, int size) {
    return sum_squared / size - (sum / size) * (sum / size);
  }
  // Calculate a blockiness level for a vertical block edge.
  // This function returns a new blockiness metric that's defined as
  
  //              p0 p1 p2 p3
  //              q0 q1 q2 q3
  // block edge ->
  //              r0 r1 r2 r3
  //              s0 s1 s2 s3
  
  // blockiness =  p0*-2+q0*6+r0*-6+s0*2 +
  //               p1*-2+q1*6+r1*-6+s1*2 +
  //               p2*-2+q2*6+r2*-6+s2*2 +
  //               p3*-2+q3*6+r3*-6+s3*2 ;
  
  // reconstructed_blockiness = abs(blockiness from reconstructed buffer -
  //                                blockiness from source buffer,0)
  //
  // I make the assumption that flat blocks are much more visible than high
  // contrast blocks. As such, I scale the result of the blockiness calc
  // by dividing the blockiness by the variance of the pixels on either side
  // of the edge as follows:
  // var_0 = (q0^2+q1^2+q2^2+q3^2) - ((q0 + q1 + q2 + q3) / 4 )^2
  // var_1 = (r0^2+r1^2+r2^2+r3^2) - ((r0 + r1 + r2 + r3) / 4 )^2
  // The returned blockiness is the scaled value
  // Reconstructed blockiness / ( 1 + var_0 + var_1 ) ;
  static int blockiness_vertical(const uint8_t *s, int sp, const uint8_t *r,
                                 int rp, int size) {
    int s_blockiness = 0;
    int r_blockiness = 0;
    int sum_0 = 0;
    int sum_sq_0 = 0;
    int sum_1 = 0;
    int sum_sq_1 = 0;
    int i;
    int var_0;
    int var_1;
    for (i = 0; i < size; ++i, s += sp, r += rp) {
      s_blockiness += horizontal_filter(s);
      r_blockiness += horizontal_filter(r);
      sum_0 += s[0];
      sum_sq_0 += s[0] * s[0];
      sum_1 += s[-1];
      sum_sq_1 += s[-1] * s[-1];
    }
    var_0 = variance(sum_0, sum_sq_0, size);
    var_1 = variance(sum_1, sum_sq_1, size);
    r_blockiness = abs(r_blockiness);
    s_blockiness = abs(s_blockiness);
  
    if (r_blockiness > s_blockiness)
      return (r_blockiness - s_blockiness) / (1 + var_0 + var_1);
    else
      return 0;
  }
  
  // Calculate a blockiness level for a horizontal block edge
  // same as above.
  static int blockiness_horizontal(const uint8_t *s, int sp, const uint8_t *r,
                                   int rp, int size) {
    int s_blockiness = 0;
    int r_blockiness = 0;
    int sum_0 = 0;
    int sum_sq_0 = 0;
    int sum_1 = 0;
    int sum_sq_1 = 0;
    int i;
    int var_0;
    int var_1;
    for (i = 0; i < size; ++i, ++s, ++r) {
      s_blockiness += vertical_filter(s, sp);
      r_blockiness += vertical_filter(r, rp);
      sum_0 += s[0];
      sum_sq_0 += s[0] * s[0];
      sum_1 += s[-sp];
      sum_sq_1 += s[-sp] * s[-sp];
    }
    var_0 = variance(sum_0, sum_sq_0, size);
    var_1 = variance(sum_1, sum_sq_1, size);
    r_blockiness = abs(r_blockiness);
    s_blockiness = abs(s_blockiness);
  
    if (r_blockiness > s_blockiness)
      return (r_blockiness - s_blockiness) / (1 + var_0 + var_1);
    else
      return 0;
  }
  
  // This function returns the blockiness for the entire frame currently by
  // looking at all borders in steps of 4.
  double vp9_get_blockiness(const uint8_t *img1, int img1_pitch,
                            const uint8_t *img2, int img2_pitch, int width,
                            int height) {
    double blockiness = 0;
    int i, j;
    vpx_clear_system_state();
    for (i = 0; i < height;
         i += 4, img1 += img1_pitch * 4, img2 += img2_pitch * 4) {
      for (j = 0; j < width; j += 4) {
        if (i > 0 && i < height && j > 0 && j < width) {
          blockiness +=
              blockiness_vertical(img1 + j, img1_pitch, img2 + j, img2_pitch, 4);
          blockiness += blockiness_horizontal(img1 + j, img1_pitch, img2 + j,
                                              img2_pitch, 4);
        }
      }
    }
    blockiness /= width * height / 16;
    return blockiness;
  }
  