ref: ea8b4a450d98726cee5ee6ab443ea85ed0309cb0
dir: /vp8/common/skin_detection.c/
/*
* 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"
#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(int cb, int cr, 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 center pixel in block to determine is_skin.
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);
}
}