80 lines
3.0 KiB
C
80 lines
3.0 KiB
C
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/*
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* Copyright (c) 2017 The WebM project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "vpx_dsp/skin_detection.h"
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#define MODEL_MODE 1
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// Fixed-point skin color model parameters.
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static const int skin_mean[5][2] = { { 7463, 9614 },
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{ 6400, 10240 },
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{ 7040, 10240 },
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{ 8320, 9280 },
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{ 6800, 9614 } };
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static const int skin_inv_cov[4] = { 4107, 1663, 1663, 2157 }; // q16
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static const int skin_threshold[6] = { 1570636, 1400000, 800000,
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800000, 800000, 800000 }; // q18
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// Thresholds on luminance.
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static const int y_low = 40;
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static const int y_high = 220;
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// Evaluates the Mahalanobis distance measure for the input CbCr values.
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static int vpx_evaluate_skin_color_difference(const int cb, const int cr,
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const int idx) {
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const int cb_q6 = cb << 6;
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const int cr_q6 = cr << 6;
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const int cb_diff_q12 =
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(cb_q6 - skin_mean[idx][0]) * (cb_q6 - skin_mean[idx][0]);
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const int cbcr_diff_q12 =
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(cb_q6 - skin_mean[idx][0]) * (cr_q6 - skin_mean[idx][1]);
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const int cr_diff_q12 =
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(cr_q6 - skin_mean[idx][1]) * (cr_q6 - skin_mean[idx][1]);
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const int cb_diff_q2 = (cb_diff_q12 + (1 << 9)) >> 10;
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const int cbcr_diff_q2 = (cbcr_diff_q12 + (1 << 9)) >> 10;
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const int cr_diff_q2 = (cr_diff_q12 + (1 << 9)) >> 10;
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const int skin_diff =
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skin_inv_cov[0] * cb_diff_q2 + skin_inv_cov[1] * cbcr_diff_q2 +
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skin_inv_cov[2] * cbcr_diff_q2 + skin_inv_cov[3] * cr_diff_q2;
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return skin_diff;
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}
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// Checks if the input yCbCr values corresponds to skin color.
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int vpx_skin_pixel(const int y, const int cb, const int cr, int motion) {
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if (y < y_low || y > y_high) {
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return 0;
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} else if (MODEL_MODE == 0) {
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return (vpx_evaluate_skin_color_difference(cb, cr, 0) < skin_threshold[0]);
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} else {
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int i = 0;
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// Exit on grey.
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if (cb == 128 && cr == 128) return 0;
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// Exit on very strong cb.
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if (cb > 150 && cr < 110) return 0;
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for (; i < 5; ++i) {
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int skin_color_diff = vpx_evaluate_skin_color_difference(cb, cr, i);
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if (skin_color_diff < skin_threshold[i + 1]) {
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if (y < 60 && skin_color_diff > 3 * (skin_threshold[i + 1] >> 2)) {
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return 0;
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} else if (motion == 0 &&
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skin_color_diff > (skin_threshold[i + 1] >> 1)) {
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return 0;
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} else {
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return 1;
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}
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}
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// Exit if difference is much large than the threshold.
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if (skin_color_diff > (skin_threshold[i + 1] << 3)) {
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return 0;
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}
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}
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return 0;
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}
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}
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