Hello!
There are 3 problems with DITHER_COPY macro in libswscale/swscale_unscaled.c:
1) there is overflow in dithering from 12-bit to 10-bit (output value > 1023);
2) for limit range the lower limit is not respected, for example from 10-bit to
8-bit value 64 is converted to 15;
3) for many iteration of downscale/upscale of the same image the 200th
iteration is significantly darker.
The first bug is due to wrong dithers table (now it is OK only for 8-bit
destination), fix is:
- const uint8_t *dither= dithers[src_depth-9][i&7];\
+ const uint8_t *dither= dithers[src_depth-dst_depth-1][i&7];\
For bugs 2) and 3) it is needed formula that do not make images darker (in
attachment). So please review.
Mateusz
diff --git a/libswscale/swscale_unscaled.c b/libswscale/swscale_unscaled.c
index ba3d688..429c98c 100644
--- a/libswscale/swscale_unscaled.c
+++ b/libswscale/swscale_unscaled.c
@@ -110,24 +110,6 @@ DECLARE_ALIGNED(8, static const uint8_t,
dithers)[8][8][8]={
{ 112, 16,104, 8,118, 22,110, 14,},
}};
-static const uint16_t dither_scale[15][16]={
-{ 2, 3, 3, 5, 5, 5, 5, 5, 5, 5, 5, 5,
5, 5, 5, 5,},
-{ 2, 3, 7, 7, 13, 13, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25,},
-{ 3, 3, 4, 15, 15, 29, 57, 57, 57, 113, 113, 113,
113, 113, 113, 113,},
-{ 3, 4, 4, 5, 31, 31, 61, 121, 241, 241, 241, 241,
481, 481, 481, 481,},
-{ 3, 4, 5, 5, 6, 63, 63, 125, 249, 497, 993, 993,
993, 993, 993, 1985,},
-{ 3, 5, 6, 6, 6, 7, 127, 127, 253, 505, 1009, 2017,
4033, 4033, 4033, 4033,},
-{ 3, 5, 6, 7, 7, 7, 8, 255, 255, 509, 1017, 2033,
4065, 8129,16257,16257,},
-{ 3, 5, 6, 8, 8, 8, 8, 9, 511, 511, 1021, 2041,
4081, 8161,16321,32641,},
-{ 3, 5, 7, 8, 9, 9, 9, 9, 10, 1023, 1023, 2045,
4089, 8177,16353,32705,},
-{ 3, 5, 7, 8, 10, 10, 10, 10, 10, 11, 2047, 2047,
4093, 8185,16369,32737,},
-{ 3, 5, 7, 8, 10, 11, 11, 11, 11, 11, 12, 4095,
4095, 8189,16377,32753,},
-{ 3, 5, 7, 9, 10, 12, 12, 12, 12, 12, 12, 13,
8191, 8191,16381,32761,},
-{ 3, 5, 7, 9, 10, 12, 13, 13, 13, 13, 13, 13,
14,16383,16383,32765,},
-{ 3, 5, 7, 9, 10, 12, 14, 14, 14, 14, 14, 14,
14, 15,32767,32767,},
-{ 3, 5, 7, 9, 11, 12, 14, 15, 15, 15, 15, 15,
15, 15, 16,65535,},
-};
-
static void fillPlane(uint8_t *plane, int stride, int width, int height, int y,
uint8_t val)
@@ -1485,22 +1467,22 @@ static int packedCopyWrapper(SwsContext *c, const
uint8_t *src[],
}
#define DITHER_COPY(dst, dstStride, src, srcStride, bswap, dbswap)\
- uint16_t scale= dither_scale[dst_depth-1][src_depth-1];\
- int shift= src_depth-dst_depth + dither_scale[src_depth-2][dst_depth-1];\
+ int scale= 31-src_depth, shift= 31-dst_depth;\
for (i = 0; i < height; i++) {\
- const uint8_t *dither= dithers[src_depth-9][i&7];\
+ const uint8_t *dither= dithers[src_depth-dst_depth-1][i&7];\
for (j = 0; j < length-7; j+=8){\
- dst[j+0] = dbswap((bswap(src[j+0]) + dither[0])*scale>>shift);\
- dst[j+1] = dbswap((bswap(src[j+1]) + dither[1])*scale>>shift);\
- dst[j+2] = dbswap((bswap(src[j+2]) + dither[2])*scale>>shift);\
- dst[j+3] = dbswap((bswap(src[j+3]) + dither[3])*scale>>shift);\
- dst[j+4] = dbswap((bswap(src[j+4]) + dither[4])*scale>>shift);\
- dst[j+5] = dbswap((bswap(src[j+5]) + dither[5])*scale>>shift);\
- dst[j+6] = dbswap((bswap(src[j+6]) + dither[6])*scale>>shift);\
- dst[j+7] = dbswap((bswap(src[j+7]) + dither[7])*scale>>shift);\
+ int32_t tmp = (bswap(src[j+0]) + (unsigned)dither[0])<<scale; tmp
= (tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+0] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+1]) + (unsigned)dither[1])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+1] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+2]) + (unsigned)dither[2])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+2] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+3]) + (unsigned)dither[3])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+3] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+4]) + (unsigned)dither[4])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+4] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+5]) + (unsigned)dither[5])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+5] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+6]) + (unsigned)dither[6])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+6] = dbswap(tmp>>shift);\
+ tmp = (bswap(src[j+7]) + (unsigned)dither[7])<<scale; tmp =
(tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j+7] = dbswap(tmp>>shift);\
+ }\
+ for (; j < length; j++){\
+ int32_t tmp = (bswap(src[j]) + (unsigned)dither[j&7])<<scale; tmp
= (tmp|(tmp>>31)) & 0x7FFFFFFF; dst[j] = dbswap(tmp>>shift);\
}\
- for (; j < length; j++)\
- dst[j] = dbswap((bswap(src[j]) + dither[j&7])*scale>>shift);\
dst += dstStride;\
src += srcStride;\
}
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