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Updated RGBtoYUV() to use the full YCbCr conversion formula

main
Sam Lantinga 2024-02-28 16:58:30 -08:00
parent 4513c32bb3
commit b30ba1c5d4
1 changed files with 43 additions and 35 deletions
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78
test/testyuv_cvt.c
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@ -48,46 +48,54 @@ static float clip3(float x, float y, float z)
static void RGBtoYUV(const Uint8 *rgb, int *yuv, YUV_CONVERSION_MODE mode, int monochrome, int luminance)
{
if (mode == YUV_CONVERSION_JPEG) {
/* Full range YUV */
yuv[0] = (int)(0.299 * rgb[0] + 0.587 * rgb[1] + 0.114 * rgb[2]);
yuv[1] = (int)((rgb[2] - yuv[0]) * 0.565 + 128);
yuv[2] = (int)((rgb[0] - yuv[0]) * 0.713 + 128);
/**
* This formula is from Microsoft's documentation:
* https://msdn.microsoft.com/en-us/library/windows/desktop/dd206750(v=vs.85).aspx
* L = Kr * R + Kb * B + (1 - Kr - Kb) * G
* Y = floor(2^(M-8) * (219*(L-Z)/S + 16) + 0.5);
* U = clip3(0, (2^M)-1, floor(2^(M-8) * (112*(B-L) / ((1-Kb)*S) + 128) + 0.5));
* V = clip3(0, (2^M)-1, floor(2^(M-8) * (112*(R-L) / ((1-Kr)*S) + 128) + 0.5));
*/
SDL_bool studio_RGB = SDL_FALSE;
SDL_bool studio_YUV = SDL_FALSE;
float N, M, S, Z, R, G, B, L, Kr, Kb, Y, U, V;
N = 8.0f; /* 8 bit RGB */
M = 8.0f; /* 8 bit YUV */
if (mode == YUV_CONVERSION_BT709) {
/* BT.709 */
Kr = 0.2126f;
Kb = 0.0722f;
} else {
/**
* This formula is from Microsoft's documentation:
* https://msdn.microsoft.com/en-us/library/windows/desktop/dd206750(v=vs.85).aspx
* L = Kr * R + Kb * B + (1 - Kr - Kb) * G
* Y = SDL_floor(2^(M-8) * (219*(L-Z)/S + 16) + 0.5);
* U = clip3(0, (2^M)-1, SDL_floor(2^(M-8) * (112*(B-L) / ((1-Kb)*S) + 128) + 0.5));
* V = clip3(0, (2^M)-1, SDL_floor(2^(M-8) * (112*(R-L) / ((1-Kr)*S) + 128) + 0.5));
*/
float S, Z, R, G, B, L, Kr, Kb, Y, U, V;
/* BT.601 */
Kr = 0.299f;
Kb = 0.114f;
}
if (mode == YUV_CONVERSION_BT709) {
/* BT.709 */
Kr = 0.2126f;
Kb = 0.0722f;
} else {
/* BT.601 */
Kr = 0.299f;
Kb = 0.114f;
}
if (mode == YUV_CONVERSION_JPEG) {
studio_YUV = SDL_FALSE;
} else {
studio_YUV = SDL_TRUE;
}
if (studio_RGB || !studio_YUV) {
S = 219.0f * SDL_powf(2.0f, N - 8);
Z = 16.0f * SDL_powf(2.0f, N - 8);
} else {
S = 255.0f;
Z = 0.0f;
R = rgb[0];
G = rgb[1];
B = rgb[2];
L = Kr * R + Kb * B + (1 - Kr - Kb) * G;
Y = (Uint8)SDL_floorf((219 * (L - Z) / S + 16) + 0.5f);
U = (Uint8)clip3(0, 255, SDL_floorf((112.0f * (B - L) / ((1.0f - Kb) * S) + 128) + 0.5f));
V = (Uint8)clip3(0, 255, SDL_floorf((112.0f * (R - L) / ((1.0f - Kr) * S) + 128) + 0.5f));
yuv[0] = (Uint8)Y;
yuv[1] = (Uint8)U;
yuv[2] = (Uint8)V;
}
R = rgb[0];
G = rgb[1];
B = rgb[2];
L = Kr * R + Kb * B + (1 - Kr - Kb) * G;
Y = SDL_floorf(SDL_powf(2.0f, (M - 8)) * (219.0f * (L - Z) / S + 16) + 0.5f);
U = clip3(0, SDL_powf(2.0f, M) - 1, SDL_floorf(SDL_powf(2.0f, (M - 8)) * (112.0f * (B - L) / ((1.0f - Kb) * S) + 128) + 0.5f));
V = clip3(0, SDL_powf(2.0f, M) - 1, SDL_floorf(SDL_powf(2.0f, (M - 8)) * (112.0f * (R - L) / ((1.0f - Kr) * S) + 128) + 0.5f));
yuv[0] = (Uint8)Y;
yuv[1] = (Uint8)U;
yuv[2] = (Uint8)V;
if (monochrome) {
yuv[1] = 128;
@ -95,7 +103,7 @@ static void RGBtoYUV(const Uint8 *rgb, int *yuv, YUV_CONVERSION_MODE mode, int m
}
if (luminance != 100) {
yuv[0] = yuv[0] * luminance / 100;
yuv[0] = (Uint8)SDL_roundf(yuv[0] * (luminance / 100.0f));
if (yuv[0] > 255) {
yuv[0] = 255;
}