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
16 namespace webrtc {
17
18 // Fixed-point skin color model parameters.
19 static const int skin_mean[2] = {7463, 9614}; // q6
20 static const int skin_inv_cov[4] = {4107, 1663, 1663, 2157}; // q16
21 static const int skin_threshold = 1570636; // q18
22
23 // Thresholds on luminance.
24 static const int y_low = 20;
25 static const int y_high = 220;
26
27 // Evaluates the Mahalanobis distance measure for the input CbCr values.
EvaluateSkinColorDifference(int cb,int cr)28 static 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
MbHasSkinColor(const uint8_t * y_src,const uint8_t * u_src,const uint8_t * v_src,const int stride_y,const int stride_u,const int stride_v,const int mb_row,const int mb_col)43 bool 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