ref: 6df142e2ab4c10f7f57e76037e68f99ccb789852
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"
#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