Function stbi__compute_y

lite/example/cpp_example/mge/cv/stb_image.h:1782–1784

//  only failure mode is malloc failing

static stbi_uc stbi__compute_y(int r, int g, int b) {
    return (stbi_uc)(((r * 77) + (g * 150) + (29 * b)) >> 8);
}
#endif

#if defined(STBI_NO_PNG) && defined(STBI_NO_BMP) && defined(STBI_NO_PSD) &&     \