1/*
2 *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10
11#include <limits.h>
12#include <math.h>
13
14#include "webrtc/modules/video_processing/util/skin_detection.h"
15
16namespace webrtc {
17
18// Fixed-point skin color model parameters.
19static const int skin_mean[2] = {7463, 9614};                 // q6
20static const int skin_inv_cov[4] = {4107, 1663, 1663, 2157};  // q16
21static const int skin_threshold = 1570636;                    // q18
22
23// Thresholds on luminance.
24static const int y_low = 20;
25static const int y_high = 220;
26
27// Evaluates the Mahalanobis distance measure for the input CbCr values.
28static int EvaluateSkinColorDifference(int cb, int cr) {
29  const int cb_q6 = cb << 6;
30  const int cr_q6 = cr << 6;
31  const int cb_diff_q12 = (cb_q6 - skin_mean[0]) * (cb_q6 - skin_mean[0]);
32  const int cbcr_diff_q12 = (cb_q6 - skin_mean[0]) * (cr_q6 - skin_mean[1]);
33  const int cr_diff_q12 = (cr_q6 - skin_mean[1]) * (cr_q6 - skin_mean[1]);
34  const int cb_diff_q2 = (cb_diff_q12 + (1 << 9)) >> 10;
35  const int cbcr_diff_q2 = (cbcr_diff_q12 + (1 << 9)) >> 10;
36  const int cr_diff_q2 = (cr_diff_q12 + (1 << 9)) >> 10;
37  const int skin_diff =
38      skin_inv_cov[0] * cb_diff_q2 + skin_inv_cov[1] * cbcr_diff_q2 +
39      skin_inv_cov[2] * cbcr_diff_q2 + skin_inv_cov[3] * cr_diff_q2;
40  return skin_diff;
41}
42
43bool MbHasSkinColor(const uint8_t* y_src,
44                    const uint8_t* u_src,
45                    const uint8_t* v_src,
46                    const int stride_y,
47                    const int stride_u,
48                    const int stride_v,
49                    const int mb_row,
50                    const int mb_col) {
51  const uint8_t* y = y_src + ((mb_row << 4) + 8) * stride_y + (mb_col << 4) + 8;
52  const uint8_t* u = u_src + ((mb_row << 3) + 4) * stride_u + (mb_col << 3) + 4;
53  const uint8_t* v = v_src + ((mb_row << 3) + 4) * stride_v + (mb_col << 3) + 4;
54  // Use 2x2 average of center pixel to compute skin area.
55  uint8_t y_avg = (*y + *(y + 1) + *(y + stride_y) + *(y + stride_y + 1)) >> 2;
56  uint8_t u_avg = (*u + *(u + 1) + *(u + stride_u) + *(u + stride_u + 1)) >> 2;
57  uint8_t v_avg = (*v + *(v + 1) + *(v + stride_v) + *(v + stride_v + 1)) >> 2;
58  // Ignore MB with too high or low brightness.
59  if (y_avg < y_low || y_avg > y_high)
60    return false;
61  else
62    return (EvaluateSkinColorDifference(u_avg, v_avg) < skin_threshold);
63}
64
65}  // namespace webrtc
66