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[devel] Made it possible to undefine PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED

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to get the same (inaccurate) output as libpng-1.5.2 and earlier.
This commit is contained in:
Glenn Randers-Pehrson
2011-06-13 11:47:00 -05:00
parent 0cb906d804
commit 141d9e3c20
3 changed files with 29 additions and 8 deletions
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13
pngrtran.c
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@@ -1439,7 +1439,11 @@ png_init_read_transformations(png_structp png_ptr)
* The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
* present, so that case is ok (until do_expand_16 is moved.)
*/
#ifdef PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
# define CHOP(x) (x)=((png_uint_16)(((png_uint_32)(x)*255+32895) >> 16))
#else
# define CHOP(x) ((png_uint_16)((2*(png_uint_32)(x) + 257)/514))
#endif
CHOP(png_ptr->background.red);
CHOP(png_ptr->background.green);
CHOP(png_ptr->background.blue);
@@ -2494,9 +2498,18 @@ png_do_chop(png_row_infop row_info, png_bytep row)
*
* (V * 255 + 32895) >> 16
*/
#ifdef PNG_LEGACY_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
*dp = *sp + ((((int)(*(sp + 1)) - *sp) > 128) ? 1 : 0);
#else
png_int_32 tmp = *sp++; /* must be signed! */
# ifdef PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
# else
sp++;
# endif
*dp++ = (png_byte)tmp;
#endif
}
row_info->bit_depth = 8;