aom_dsp/ssim.c

/*
 * Copyright (c) 2021, Alliance for Open Media. All rights reserved
 *
 * This source code is subject to the terms of the BSD 3-Clause Clear License
 * and the Alliance for Open Media Patent License 1.0. If the BSD 3-Clause Clear
 * License was not distributed with this source code in the LICENSE file, you
 * can obtain it at aomedia.org/license/software-license/bsd-3-c-c/.  If the
 * Alliance for Open Media Patent License 1.0 was not distributed with this
 * source code in the PATENTS file, you can obtain it at
 * aomedia.org/license/patent-license/.
 */

#include <assert.h>
#include <math.h>

#include "config/aom_dsp_rtcd.h"

#include "aom_dsp/ssim.h"
#include "aom_ports/mem.h"
#include "aom_ports/system_state.h"

void aom_highbd_ssim_parms_8x8_c(const uint16_t *s, int sp, const uint16_t *r,
                                 int rp, uint32_t *sum_s, uint32_t *sum_r,
                                 uint32_t *sum_sq_s, uint32_t *sum_sq_r,
                                 uint32_t *sum_sxr) {
  int i, j;
  for (i = 0; i < 8; i++, s += sp, r += rp) {
    for (j = 0; j < 8; j++) {
      *sum_s += s[j];
      *sum_r += r[j];
      *sum_sq_s += s[j] * s[j];
      *sum_sq_r += r[j] * r[j];
      *sum_sxr += s[j] * r[j];
    }
  }
}

static const int64_t cc1 = 26634;        // (64^2*(.01*255)^2
static const int64_t cc2 = 239708;       // (64^2*(.03*255)^2
static const int64_t cc1_10 = 428658;    // (64^2*(.01*1023)^2
static const int64_t cc2_10 = 3857925;   // (64^2*(.03*1023)^2
static const int64_t cc1_12 = 6868593;   // (64^2*(.01*4095)^2
static const int64_t cc2_12 = 61817334;  // (64^2*(.03*4095)^2

static double similarity(uint32_t sum_s, uint32_t sum_r, uint32_t sum_sq_s,
                         uint32_t sum_sq_r, uint32_t sum_sxr, int count,
                         uint32_t bd) {
  double ssim_n, ssim_d;
  int64_t c1, c2;
  if (bd == 8) {
    // scale the constants by number of pixels
    c1 = (cc1 * count * count) >> 12;
    c2 = (cc2 * count * count) >> 12;
  } else if (bd == 10) {
    c1 = (cc1_10 * count * count) >> 12;
    c2 = (cc2_10 * count * count) >> 12;
  } else if (bd == 12) {
    c1 = (cc1_12 * count * count) >> 12;
    c2 = (cc2_12 * count * count) >> 12;
  } else {
    c1 = c2 = 0;
    assert(0);
  }

  ssim_n = (2.0 * sum_s * sum_r + c1) *
           (2.0 * count * sum_sxr - 2.0 * sum_s * sum_r + c2);

  ssim_d = ((double)sum_s * sum_s + (double)sum_r * sum_r + c1) *
           ((double)count * sum_sq_s - (double)sum_s * sum_s +
            (double)count * sum_sq_r - (double)sum_r * sum_r + c2);

  return ssim_n / ssim_d;
}

static double highbd_ssim_8x8(const uint16_t *s, int sp, const uint16_t *r,
                              int rp, uint32_t bd, uint32_t shift) {
  uint32_t sum_s = 0, sum_r = 0, sum_sq_s = 0, sum_sq_r = 0, sum_sxr = 0;
  aom_highbd_ssim_parms_8x8(s, sp, r, rp, &sum_s, &sum_r, &sum_sq_s, &sum_sq_r,
                            &sum_sxr);
  return similarity(sum_s >> shift, sum_r >> shift, sum_sq_s >> (2 * shift),
                    sum_sq_r >> (2 * shift), sum_sxr >> (2 * shift), 64, bd);
}

// We are using a 8x8 moving window with starting location of each 8x8 window
// on the 4x4 pixel grid. Such arrangement allows the windows to overlap
// block boundaries to penalize blocking artifacts.
static double aom_highbd_ssim2(const uint16_t *img1, const uint16_t *img2,
                               int stride_img1, int stride_img2, int width,
                               int height, uint32_t bd, uint32_t shift) {
  int i, j;
  int samples = 0;
  double ssim_total = 0;

  // sample point start with each 4x4 location
  for (i = 0; i <= height - 8;
       i += 4, img1 += stride_img1 * 4, img2 += stride_img2 * 4) {
    for (j = 0; j <= width - 8; j += 4) {
      double v = highbd_ssim_8x8(img1 + j, stride_img1, img2 + j, stride_img2,
                                 bd, shift);
      ssim_total += v;
      samples++;
    }
  }
  ssim_total /= samples;
  return ssim_total;
}

double aom_highbd_calc_ssim(const YV12_BUFFER_CONFIG *source,
                            const YV12_BUFFER_CONFIG *dest, double *weight,
                            uint32_t bd, uint32_t in_bd) {
  assert(bd >= in_bd);
  const uint32_t shift = bd - in_bd;

  double abc[3];
  for (int i = 0; i < 3; ++i) {
    const int is_uv = i > 0;
    abc[i] = aom_highbd_ssim2(source->buffers[i], dest->buffers[i],
                              source->strides[is_uv], dest->strides[is_uv],
                              source->crop_widths[is_uv],
                              source->crop_heights[is_uv], in_bd, shift);
  }

  *weight = 1;
  return abc[0] * .8 + .1 * (abc[1] + abc[2]);
}