+}
+
+void convert_ycbcr()
+{
+ double coeff[3] = { 0.2126, 0.7152, 0.0722 }; // sum = 1.0
+ double cb_fac = 1.0 / (coeff[0] + coeff[1] + 1.0f - coeff[2]); // 0.539
+ double cr_fac = 1.0 / (1.0f - coeff[0] + coeff[1] + coeff[2]); // 0.635
+
+ unique_ptr<float[]> temp_cb(new float[WIDTH * HEIGHT]);
+ unique_ptr<float[]> temp_cr(new float[WIDTH * HEIGHT]);
+ for (unsigned yb = 0; yb < HEIGHT; ++yb) {
+ for (unsigned xb = 0; xb < WIDTH; ++xb) {
+ int r = rgb[((yb * WIDTH) + xb) * 3 + 0];
+ int g = rgb[((yb * WIDTH) + xb) * 3 + 1];
+ int b = rgb[((yb * WIDTH) + xb) * 3 + 2];
+ double y = std::min(std::max(coeff[0] * r + coeff[1] * g + coeff[2] * b, 0.0), 255.0);
+ double cb = (b - y) * cb_fac + 128.0;
+ double cr = (r - y) * cr_fac + 128.0;
+ pix_y[(yb * WIDTH) + xb] = lrint(y);
+ temp_cb[(yb * WIDTH) + xb] = cb;
+ temp_cr[(yb * WIDTH) + xb] = cr;
+ full_pix_cb[(yb * WIDTH) + xb] = lrint(std::min(std::max(cb, 0.0), 255.0));
+ full_pix_cr[(yb * WIDTH) + xb] = lrint(std::min(std::max(cr, 0.0), 255.0));
+ }
+ }
+
+ // Simple 4:2:2 subsampling with left convention.
+ for (unsigned yb = 0; yb < HEIGHT; ++yb) {
+ for (unsigned xb = 0; xb < WIDTH / 2; ++xb) {
+ int c0 = yb * WIDTH + std::max(int(xb) * 2 - 1, 0);
+ int c1 = yb * WIDTH + xb * 2;
+ int c2 = yb * WIDTH + xb * 2 + 1;
+
+ double cb = 0.25 * temp_cb[c0] + 0.5 * temp_cb[c1] + 0.25 * temp_cb[c2];
+ double cr = 0.25 * temp_cr[c0] + 0.5 * temp_cr[c1] + 0.25 * temp_cr[c2];
+ cb = std::min(std::max(cb, 0.0), 255.0);
+ cr = std::min(std::max(cr, 0.0), 255.0);
+ pix_cb[(yb * WIDTH/2) + xb] = lrint(cb);
+ pix_cr[(yb * WIDTH/2) + xb] = lrint(cr);
+ }
+ }
+}
+
+int main(int argc, char **argv)
+{
+ if (argc >= 2)
+ readpix(rgb, argv[1]);
+ else
+ readpix(rgb, "color.pnm");
+ convert_ycbcr();