44 lines
1.7 KiB
C
44 lines
1.7 KiB
C
#include "robot36.h"
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#include "sstv.h"
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#include <stdint.h>
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// From Dayton Paper Appendix B - ITU BT.601
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// http://www.barberdsp.com/downloads/Dayton%20Paper.pdf
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static void rgb_to_ycbcr(uint8_t r, uint8_t g, uint8_t b,
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double *Y, double *RY, double *BY) {
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*Y = 16.0 + .003906 * ((65.738 * r) + (129.057 * g) + (25.064 * b));
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*RY = 128.0 + .003906 * ((112.439 * r) + (-94.154 * g) + (-18.285 * b));
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*BY = 128.0 + .003906 * ((-37.945 * r) + (-74.494 * g) + (112.439 * b));
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}
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static void scan_line_y(wav_t *wav, uint8_t *line) {
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for (int x = 0; x < ROBOT36_WIDTH; x++) {
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double Y, RY, BY;
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rgb_to_ycbcr(line[x*3+0], line[x*3+1], line[x*3+2], &Y, &RY, &BY);
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sstv_tone(wav, 1500.0 + Y * 3.1372549, 88.0 / ROBOT36_WIDTH);
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}
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}
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static void scan_line_chroma(wav_t *wav, uint8_t *line, int is_ry) {
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for (int x = 0; x < ROBOT36_WIDTH; x++) {
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double Y, RY, BY;
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rgb_to_ycbcr(line[x*3+0], line[x*3+1], line[x*3+2], &Y, &RY, &BY);
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double c = is_ry ? RY : BY;
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sstv_tone(wav, 1500.0 + c * 3.1372549, 44.0 / ROBOT36_WIDTH);
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}
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}
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void robot36_encode_image(wav_t *wav, uint8_t *rgb) {
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for (int y = 0; y < ROBOT36_HEIGHT; y++) {
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uint8_t *line = &rgb[y * ROBOT36_WIDTH * 3];
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int even = (y % 2 == 0);
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sstv_tone(wav, 1200, 9.0); // sync
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sstv_tone(wav, 1500, 3.0); // sync porch
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scan_line_y(wav, line);
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sstv_tone(wav, even ? 1500 : 2300, 4.5); // separator - tells decoder Cr vs Cb!
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sstv_tone(wav, 1900, 1.5); // porch before chroma
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scan_line_chroma(wav, line, even); // Cr on even, Cb on odd
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}
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}
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