shithub: libvpx

ref: c12d1d9b982e8717d2d7cabe3230105948bd3b7a
dir: /vp8/common/skin_detection.c/

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/*
 *  Copyright (c) 2015 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 "vp8/common/skin_detection.h"
#include "vp8/common/alloccommon.h"
#include "vpx_dsp/vpx_dsp_common.h"
#include "vpx_mem/vpx_mem.h"

#define MODEL_MODE 1

// Fixed-point skin color model parameters.
static const int skin_mean[5][2] = { { 7463, 9614 },
                                     { 6400, 10240 },
                                     { 7040, 10240 },
                                     { 8320, 9280 },
                                     { 6800, 9614 } };
static const int skin_inv_cov[4] = { 4107, 1663, 1663, 2157 };  // q16
static const int skin_threshold[6] = { 1570636, 1400000, 800000,
                                       800000,  800000,  800000 };  // q18

// Thresholds on luminance.
static const int y_low = 40;
static const int y_high = 220;

// Evaluates the Mahalanobis distance measure for the input CbCr values.
static int evaluate_skin_color_difference(const int cb, const int cr,
                                          const int idx) {
  const int cb_q6 = cb << 6;
  const int cr_q6 = cr << 6;
  const int cb_diff_q12 =
      (cb_q6 - skin_mean[idx][0]) * (cb_q6 - skin_mean[idx][0]);
  const int cbcr_diff_q12 =
      (cb_q6 - skin_mean[idx][0]) * (cr_q6 - skin_mean[idx][1]);
  const int cr_diff_q12 =
      (cr_q6 - skin_mean[idx][1]) * (cr_q6 - skin_mean[idx][1]);
  const int cb_diff_q2 = (cb_diff_q12 + (1 << 9)) >> 10;
  const int cbcr_diff_q2 = (cbcr_diff_q12 + (1 << 9)) >> 10;
  const int cr_diff_q2 = (cr_diff_q12 + (1 << 9)) >> 10;
  const int skin_diff =
      skin_inv_cov[0] * cb_diff_q2 + skin_inv_cov[1] * cbcr_diff_q2 +
      skin_inv_cov[2] * cbcr_diff_q2 + skin_inv_cov[3] * cr_diff_q2;
  return skin_diff;
}

// Checks if the input yCbCr values corresponds to skin color.
int skin_pixel(int y, int cb, int cr, int motion) {
  if (y < y_low || y > y_high) {
    return 0;
  } else {
    if (MODEL_MODE == 0) {
      return (evaluate_skin_color_difference(cb, cr, 0) < skin_threshold[0]);
    } else {
      int i = 0;
      // Exit on grey.
      if (cb == 128 && cr == 128) return 0;
      // Exit on very strong cb.
      if (cb > 150 && cr < 110) return 0;
      for (; i < 5; ++i) {
        int skin_color_diff = evaluate_skin_color_difference(cb, cr, i);
        if (skin_color_diff < skin_threshold[i + 1]) {
          if (y < 60 && skin_color_diff > 3 * (skin_threshold[i + 1] >> 2)) {
            return 0;
          } else if (motion == 0 &&
                     skin_color_diff > (skin_threshold[i + 1] >> 1)) {
            return 0;
          } else {
            return 1;
          }
        }
        // Exit if difference is much large than the threshold.
        if (skin_color_diff > (skin_threshold[i + 1] << 3)) {
          return 0;
        }
      }
      return 0;
    }
  }
}

int compute_skin_block(const uint8_t *y, const uint8_t *u, const uint8_t *v,
                       int stride, int strideuv, int consec_zeromv,
                       int curr_motion_magn) {
  // No skin if block has been zero/small motion for long consecutive time.
  if (consec_zeromv > 60 && curr_motion_magn == 0) {
    return 0;
  } else {
    int motion = 1;
    // Take the average of center 2x2 pixels.
    const int ysource = (y[7 * stride + 7] + y[7 * stride + 8] +
                         y[8 * stride + 7] + y[8 * stride + 8]) >>
                        2;
    const int usource = (u[3 * strideuv + 3] + u[3 * strideuv + 4] +
                         u[4 * strideuv + 3] + u[4 * strideuv + 4]) >>
                        2;
    const int vsource = (v[3 * strideuv + 3] + v[3 * strideuv + 4] +
                         v[4 * strideuv + 3] + v[4 * strideuv + 4]) >>
                        2;
    if (consec_zeromv > 25 && curr_motion_magn == 0) motion = 0;
    return skin_pixel(ysource, usource, vsource, motion);
  }
}

#ifdef OUTPUT_YUV_SKINMAP
// For viewing skin map on input source.
void compute_skin_map(VP8_COMP *const cpi, FILE *yuv_skinmap_file) {
  int i, j, mb_row, mb_col, num_bl;
  VP8_COMMON *const cm = &cpi->common;
  uint8_t *y;
  const uint8_t *src_y = cpi->Source->y_buffer;
  const uint8_t *src_u = cpi->Source->u_buffer;
  const uint8_t *src_v = cpi->Source->v_buffer;
  const int src_ystride = cpi->Source->y_stride;
  const int src_uvstride = cpi->Source->uv_stride;

  YV12_BUFFER_CONFIG skinmap;
  memset(&skinmap, 0, sizeof(skinmap));
  if (vp8_yv12_alloc_frame_buffer(&skinmap, cm->Width, cm->Height,
                                  VP8BORDERINPIXELS) < 0) {
    vpx_free_frame_buffer(&skinmap);
    return;
  }
  memset(skinmap.buffer_alloc, 128, skinmap.frame_size);
  y = skinmap.y_buffer;
  // Loop through blocks and set skin map based on center pixel of block.
  // Set y to white for skin block, otherwise set to source with gray scale.
  // Ignore rightmost/bottom boundary blocks.
  for (mb_row = 0; mb_row < cm->mb_rows; mb_row += 1) {
    num_bl = 0;
    for (mb_col = 0; mb_col < cm->mb_cols; mb_col += 1) {
      int is_skin = 0;
      int consec_zeromv = 0;
      const int bl_index = mb_row * cm->mb_cols + mb_col;
      const int bl_index1 = bl_index + 1;
      const int bl_index2 = bl_index + cm->mb_cols;
      const int bl_index3 = bl_index2 + 1;
      consec_zeromv = VPXMIN(cpi->consec_zero_last[bl_index],
                             VPXMIN(cpi->consec_zero_last[bl_index1],
                                    VPXMIN(cpi->consec_zero_last[bl_index2],
                                           cpi->consec_zero_last[bl_index3])));
      is_skin = compute_skin_block(src_y, src_u, src_v, src_ystride,
                                   src_uvstride, consec_zeromv, 0);
      for (i = 0; i < 16; i++) {
        for (j = 0; j < 16; j++) {
          if (is_skin)
            y[i * src_ystride + j] = 255;
          else
            y[i * src_ystride + j] = src_y[i * src_ystride + j];
        }
      }
      num_bl++;
      y += 16;
      src_y += 16;
      src_u += 8;
      src_v += 8;
    }
    y += (src_ystride << 4) - (num_bl << 4);
    src_y += (src_ystride << 4) - (num_bl << 4);
    src_u += (src_uvstride << 3) - (num_bl << 3);
    src_v += (src_uvstride << 3) - (num_bl << 3);
  }
  vp8_write_yuv_frame(yuv_skinmap_file, &skinmap);
  vpx_free_frame_buffer(&skinmap);
}
#endif  // OUTPUT_YUV_SKINMAP