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Fixed bug 3857 - SDL_ConvertPixels misses YUV conversions
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Sylvain

There are various YUV-RGB conversion coefficients, according to https://www.fourcc.org/fccyvrgb.php
I choose the first (from Video Demystified, with integer multiplication),
but the current SDL2 Dither functions use in fact the next one, which follows a specifications called CCIR 601.

Here's a patch to use the second ones and with previous warning corrections.
There are less multiplications involved because Chroma coefficient is 1.
Also, doing float multiplication is as efficient with vectorization.
In the end, the YUV decoding is faster: ~165 ms vs my previous 195 ms.

Moreover, if SDL2 is compiled with -march=native, then YUV decoding time drops to ~130ms, while older ones remains around ~220 ms.


For information, from jpeg-9 source code:
jpeg-9/jccolor.c

   * YCbCr is defined per CCIR 601-1, except that Cb and Cr are
   * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
   * The conversion equations to be implemented are therefore
   * Y  =  0.29900 * R + 0.58700 * G + 0.11400 * B
   * Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B  + CENTERJSAMPLE
   * Cr =  0.50000 * R - 0.41869 * G - 0.08131 * B  + CENTERJSAMPLE

jpeg-9/jdcolor.c

   * YCbCr is defined per CCIR 601-1, except that Cb and Cr are
   * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
   * The conversion equations to be implemented are therefore
   *
   * R = Y                + 1.40200 * Cr
   * G = Y - 0.34414 * Cb - 0.71414 * Cr
   * B = Y + 1.77200 * Cb
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@slouken
slouken committed Oct 7, 2017
1 parent 1bfe6d6 commit d2a2b0c
Showing 1 changed file with 29 additions and 10 deletions.
39 changes: 29 additions & 10 deletions src/video/SDL_surface.c
View file
Expand Up @@ -1176,7 +1176,7 @@ int SDL_ConvertPixels(int width, int height,
dst_pitch = (dst_pitch + 1) / 2;
for (i = height * 2; i--;) {
SDL_memcpy(dst, src, width);
src = (Uint8*)src + src_pitch;
src = (const Uint8*)src + src_pitch;
dst = (Uint8*)dst + dst_pitch;
}
} else if (src_format == SDL_PIXELFORMAT_NV12 || src_format == SDL_PIXELFORMAT_NV21) {
Expand All @@ -1187,7 +1187,7 @@ int SDL_ConvertPixels(int width, int height,
dst_pitch = (dst_pitch + 1) / 2;
for (i = height; i--;) {
SDL_memcpy(dst, src, 2 * width);
src = (Uint8*)src + 2 * src_pitch;
src = (const Uint8*)src + 2 * src_pitch;
dst = (Uint8*)dst + 2 * dst_pitch;
}
}
Expand Down Expand Up @@ -1321,15 +1321,31 @@ SDL_FreeSurface(SDL_Surface * surface)
/* YUV-RGB conversion */
#define CLAMP(val) ((val) > 0 ? ((val) < 255 ? (val) : 255) : 0)

#if 1

/* Coefficients from CCIR 601 */
#define MAKE_Y(r, g, b) (int)( 0.29900f * (r) + 0.58700f * (g) + 0.11400f * (b))
#define MAKE_U(r, g, b) (int)(-0.16874f * (r) - 0.33126f * (g) + 0.50000f * (b) + 128)
#define MAKE_V(r, g, b) (int)( 0.50000f * (r) - 0.41869f * (g) - 0.08131f * (b) + 128)

#define MAKE_R(y, u, v) CLAMP((int)((y) + 1.40200f * ((v) - 128)))
#define MAKE_G(y, u, v) CLAMP((int)((y) - 0.34414f * ((u) - 128) - 0.71414f * ((v) - 128)))
#define MAKE_B(y, u, v) CLAMP((int)((y) + 1.77200f * ((u) - 128) ))

#else

/* Coefficients from Video Demystified */
#define MAKE_Y(r, g, b) ((( 66 * (r) + 129 * (g) + 25 * (b) + 128) >> 8) + 16)
#define MAKE_U(r, g, b) ((( -38 * (r) - 74 * (g) + 112 * (b) + 128) >> 8) + 128)
#define MAKE_V(r, g, b) ((( 112 * (r) - 94 * (g) - 18 * (b) + 128) >> 8) + 128)


#define MAKE_R(y, u, v) CLAMP(( 298 * ((y) - 16) + 409 * ((v) - 128) + 128) >> 8)
#define MAKE_G(y, u, v) CLAMP(( 298 * ((y) - 16) - 100 * ((u) - 128) - 208 * ((v) - 128) + 128) >> 8)
#define MAKE_B(y, u, v) CLAMP(( 298 * ((y) - 16) + 516 * ((u) - 128) + 128) >> 8)

#endif


static int
SDL_ConvertPixels_YUV_to_ARGB8888(int width, int height,
Uint32 src_format, const void *src,
Expand Down Expand Up @@ -1465,7 +1481,8 @@ SDL_ConvertPixels_YUV_to_ARGB8888(int width, int height,
WRITE_RGB_PIXEL(y1, u, v);
}
if (width_remainder) {
READ_PACKED_YUV(y, u, y1, v); /* y1 unused */
READ_PACKED_YUV(y, u, y1, v);
(void)y1; /* y1 unused */
WRITE_RGB_PIXEL(y, u, v);
}
curr_row += curr_row_padding;
Expand All @@ -1480,7 +1497,8 @@ SDL_ConvertPixels_YUV_to_ARGB8888(int width, int height,
WRITE_RGB_PIXEL(y1, u, v);
}
if (width_remainder) {
READ_PACKED_YUV(u, y, v, y1); /* y1 unused */
READ_PACKED_YUV(u, y, v, y1);
(void) y1; /* y1 unused */
WRITE_RGB_PIXEL(y, u, v);
}
curr_row += curr_row_padding;
Expand All @@ -1495,7 +1513,8 @@ SDL_ConvertPixels_YUV_to_ARGB8888(int width, int height,
WRITE_RGB_PIXEL(y1, u, v);
}
if (width_remainder) {
READ_PACKED_YUV(y, v, y1, u); /* y1 unused */
READ_PACKED_YUV(y, v, y1, u);
(void) y1; /* y1 unused */
WRITE_RGB_PIXEL(y, u, v);
}
curr_row += curr_row_padding;
Expand Down Expand Up @@ -1557,10 +1576,10 @@ SDL_ConvertPixels_ARGB8888_to_YUV(int width, int height, const void *src, int sr
#if 1
/* slightly faster */
#define READ_2x2_PIXELS \
const Uint32 p1 = ((Uint32 *)curr_row)[2 * i]; \
const Uint32 p2 = ((Uint32 *)curr_row)[2 * i + 1]; \
const Uint32 p3 = ((Uint32 *)next_row)[2 * i]; \
const Uint32 p4 = ((Uint32 *)next_row)[2 * i + 1]; \
const Uint32 p1 = ((const Uint32 *)curr_row)[2 * i]; \
const Uint32 p2 = ((const Uint32 *)curr_row)[2 * i + 1]; \
const Uint32 p3 = ((const Uint32 *)next_row)[2 * i]; \
const Uint32 p4 = ((const Uint32 *)next_row)[2 * i + 1]; \
const Uint32 b = ((p1 & 0x000000ff) + (p2 & 0x000000ff) + (p3 & 0x000000ff) + (p4 & 0x000000ff)) >> 2; \
const Uint32 g = ((p1 & 0x0000ff00) + (p2 & 0x0000ff00) + (p3 & 0x0000ff00) + (p4 & 0x0000ff00)) >> 10; \
const Uint32 r = ((p1 & 0x00ff0000) + (p2 & 0x00ff0000) + (p3 & 0x00ff0000) + (p4 & 0x00ff0000)) >> 18; \
Expand Down

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