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[libpng15] Installed more accurate linear to sRGB conversion tables.
The slightly modified tables reduce the number of 16-bit values that convert to an off-by-one 8-bit value. The "makesRGB.c" code that was used to generate the tables is now in a contrib/sRGBtables sub-directory.
This commit is contained in:
John Bowler
committed by
Glenn Randers-Pehrson
Glenn Randers-Pehrson
parent
d3feb52955
commit
0a521d3785
270
png.c
270
png.c
@@ -645,13 +645,13 @@ png_get_copyright(png_const_structp png_ptr)
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#else
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# ifdef __STDC__
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return PNG_STRING_NEWLINE \
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"libpng version 1.5.7beta02 - November 10, 2011" PNG_STRING_NEWLINE \
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"libpng version 1.5.7beta02 - November 12, 2011" PNG_STRING_NEWLINE \
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"Copyright (c) 1998-2011 Glenn Randers-Pehrson" PNG_STRING_NEWLINE \
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"Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
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"Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
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PNG_STRING_NEWLINE;
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# else
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return "libpng version 1.5.7beta02 - November 10, 2011\
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return "libpng version 1.5.7beta02 - November 12, 2011\
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Copyright (c) 1998-2011 Glenn Randers-Pehrson\
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Copyright (c) 1996-1997 Andreas Dilger\
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Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
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@@ -2858,173 +2858,21 @@ png_build_gamma_table(png_structp png_ptr, int bit_depth)
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/* sRGB support */
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#if defined PNG_SIMPLIFIED_READ_SUPPORTED ||\
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defined PNG_SIMPLIFIED_WRITE_SUPPORTED
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/* sRGB conversion tables; these are machine generated with the following code.
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/* sRGB conversion tables; these are machine generated with the code in
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* contrib/sRGBtables/makesRGB.c. The sRGB to linear table is exact (to the
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* nearest 16 bit linear fraction). The inverse (linear to sRGB) table has
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* accuracies as follows:
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*
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* For all possible (255*65535+1) input values:
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*
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* error: -0.515566 - 0.625971, 79441 (0.475369%) of readings inexact
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*
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* For the input values corresponding to the 65536 16-bit values:
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*
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* error: -0.513727 - 0.607759, 308 (0.469978%) of readings inexact
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*
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* In all cases the inexact readings are off by one.
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*/
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#ifdef PNG_INCLUDE_SELF_GENERATING_AND_SELF_DOCUMENTING_CODE
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#define _C99_SOURCE 1
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#include <stdio.h>
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#include <math.h>
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#include <stdlib.h>
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static unsigned int max_input = 255*65535;
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double sRGB(unsigned int i)
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{
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double l = i;
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l /= max_input;
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if (l <= 0.0031308)
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l *= 12.92;
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else
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l = 1.055 * pow(l, 1/2.4) - 0.055;
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return l;
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}
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unsigned int invsRGB(unsigned int i)
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{
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double l = i/255.;
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if (l <= 0.04045)
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l /= 12.92;
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else
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l = pow((l+0.055)/1.055, 2.4);
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l *= 65535;
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return nearbyint(l);
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}
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int main(void)
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{
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unsigned int i, i16;
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unsigned short base[512];
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unsigned char delta[512];
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double max_error = 0;
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double max_error16 = 0;
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unsigned int error_count = 0;
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unsigned int error_count16 = 0;
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for (i=0; i<=511; ++i)
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{
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double lo = 255 * sRGB(i << 15);
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double hi = 255 * sRGB((i+1) << 15);
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unsigned int calc;
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calc = nearbyint((lo+.5) * 256);
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if (calc > 65535)
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{
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fprintf(stderr, "table[%d][0]: overflow %08x (%d)\n", i, calc, calc);
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exit(1);
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}
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base[i] = calc;
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calc = nearbyint((hi-lo) * 32);
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if (calc > 255)
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{
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fprintf(stderr, "table[%d][1]: overflow %08x (%d)\n", i, calc, calc);
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exit(1);
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}
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delta[i] = calc;
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}
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for (i=0; i <= max_input; ++i)
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{
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unsigned int iexact = nearbyint(255*sRGB(i));
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unsigned int icalc = base[i>>15] + (((i&0x7fff)*delta[i>>15])>>12);
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icalc >>= 8;
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if (icalc != iexact)
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{
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double err = fabs(255*sRGB(i) - icalc);
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++error_count;
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if (err > .646)
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{
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printf(
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"/* 0x%08x: exact: %3d, got: %3d [tables: %08x, %08x] (%f) */\n",
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i, iexact, icalc, base[i>>15], delta[i>>15], err);
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if (err > max_error)
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max_error = err;
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}
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}
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}
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for (i16=0; i16 <= 65535; ++i16)
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{
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unsigned int i = 255*i16;
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unsigned int iexact = nearbyint(255*sRGB(i));
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unsigned int icalc = base[i>>15] + (((i&0x7fff)*delta[i>>15])>>12);
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icalc >>= 8;
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if (icalc != iexact)
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{
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double err = fabs(255*sRGB(i) - icalc);
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++error_count16;
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if (err > max_error16)
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max_error16 = err;
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if (abs(icalc - iexact) > 1)
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printf(
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"/* 0x%04x: exact: %3d, got: %3d [tables: %08x, %08x] (%f) */\n",
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i16, iexact, icalc, base[i>>15], delta[i>>15], err);
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}
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}
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printf("/* maximum error: %g, %g%% of readings */\n", max_error,
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(100.*error_count)/max_input);
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printf("/* maximum 16-bit error: %g, %g%% of readings */\n", max_error16,
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(100.*error_count16)/65535);
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printf("PNG_CONST png_uint_16 png_sRGB_table[256] =\n{\n ");
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for (i=0; i<255; )
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{
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do
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{
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printf("%d,", invsRGB(i++));
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}
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while ((i & 0x7) != 0 && i<255);
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if (i<255) printf("\n ");
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}
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printf("%d\n};\n\n", invsRGB(i));
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printf("PNG_CONST png_uint_16 png_sRGB_base[512] =\n{\n ");
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for (i=0; i<511; )
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{
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do
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{
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printf("%d,", base[i++]);
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}
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while ((i & 0x7) != 0 && i<511);
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if (i<511) printf("\n ");
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}
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printf("%d\n};\n\n", base[i]);
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printf("PNG_CONST png_byte png_sRGB_delta[512] =\n{\n ");
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for (i=0; i<511; )
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{
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do
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{
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printf("%d,", delta[i++]);
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}
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while ((i & 0xf) != 0 && i<511);
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if (i<511) printf("\n ");
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}
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printf("%d\n};\n\n", delta[i]);
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return 0;
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}
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#endif /* self documenting code */
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/* The result is a set of tables with the following errors: */
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/* 0x000148c1: exact: 16, got: 15 [tables: 00000d36, 0000009d] (0.646071) */
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/* 0x000148c2: exact: 16, got: 15 [tables: 00000d36, 0000009d] (0.646218) */
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/* 0x000148c3: exact: 16, got: 15 [tables: 00000d36, 0000009d] (0.646365) */
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/* maximum error: 0.646365, 0.494416% of readings */
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/* maximum 16-bit error: 0.644455, 0.5066% of readings */
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#ifdef PNG_SIMPLIFIED_READ_SUPPORTED
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/* The convert-to-sRGB table is only currently required for read. */
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@@ -3063,6 +2911,7 @@ PNG_CONST png_uint_16 png_sRGB_table[256] =
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57105,57646,58190,58737,59287,59840,60396,60955,
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61517,62082,62650,63221,63795,64372,64952,65535
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};
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#endif /* simplified read only */
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/* The base/delta tables are required for both read and write (but currently
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@@ -3070,52 +2919,52 @@ PNG_CONST png_uint_16 png_sRGB_table[256] =
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*/
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PNG_CONST png_uint_16 png_sRGB_base[512] =
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{
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128,1782,3382,4641,5673,6563,7355,8072,
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8732,9346,9920,10463,10977,11466,11935,12384,
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12815,13232,13634,14024,14402,14768,15125,15473,
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15811,16142,16465,16781,17090,17393,17689,17980,
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128,1782,3383,4644,5675,6564,7357,8074,
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8732,9346,9921,10463,10977,11466,11935,12384,
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12816,13233,13634,14024,14402,14769,15125,15473,
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15812,16142,16466,16781,17090,17393,17690,17981,
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18266,18546,18822,19093,19359,19621,19879,20133,
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20383,20630,20873,21113,21349,21583,21813,22040,
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22265,22487,22706,22923,23138,23350,23559,23767,
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20383,20630,20873,21113,21349,21583,21813,22041,
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22265,22487,22707,22923,23138,23350,23559,23767,
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23972,24175,24376,24575,24772,24967,25160,25352,
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25541,25729,25916,26100,26283,26465,26645,26823,
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27000,27176,27350,27523,27694,27865,28033,28201,
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25542,25730,25916,26101,26284,26465,26645,26823,
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27000,27176,27350,27523,27695,27865,28034,28201,
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28368,28533,28697,28860,29021,29182,29341,29500,
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29657,29813,29969,30123,30276,30428,30580,30730,
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29657,29813,29969,30123,30276,30429,30580,30730,
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30880,31028,31176,31323,31469,31614,31758,31902,
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32044,32186,32327,32468,32607,32746,32884,33021,
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33158,33294,33429,33563,33697,33830,33963,34095,
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34226,34356,34486,34616,34744,34872,35000,35127,
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32045,32186,32327,32468,32607,32746,32884,33021,
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33158,33294,33429,33564,33697,33831,33963,34095,
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34226,34357,34486,34616,34744,34873,35000,35127,
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35253,35379,35504,35629,35753,35876,35999,36122,
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36244,36365,36486,36606,36726,36845,36964,37083,
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37201,37318,37435,37551,37667,37783,37898,38013,
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37201,37318,37435,37551,37668,37783,37898,38013,
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38127,38241,38354,38467,38580,38692,38803,38915,
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39025,39136,39246,39356,39465,39574,39682,39790,
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39026,39136,39246,39356,39465,39574,39682,39790,
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39898,40005,40112,40219,40325,40431,40537,40642,
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40747,40851,40955,41059,41163,41266,41369,41471,
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41573,41675,41776,41878,41978,42079,42179,42279,
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42379,42478,42577,42676,42774,42873,42970,43068,
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43165,43262,43359,43455,43552,43647,43743,43838,
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43934,44028,44123,44217,44311,44405,44498,44592,
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44685,44777,44870,44962,45054,45146,45238,45329,
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41573,41675,41777,41878,41979,42079,42179,42279,
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42379,42478,42577,42676,42775,42873,42971,43068,
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43165,43262,43359,43456,43552,43648,43743,43839,
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43934,44028,44123,44217,44311,44405,44499,44592,
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44685,44778,44870,44962,45054,45146,45238,45329,
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45420,45511,45601,45692,45782,45872,45961,46051,
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46140,46229,46318,46406,46494,46582,46670,46758,
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46845,46933,47020,47107,47193,47280,47366,47452,
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47538,47623,47708,47794,47879,47963,48048,48132,
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48217,48301,48384,48468,48552,48635,48718,48801,
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48884,48966,49048,49131,49213,49294,49376,49457,
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49539,49620,49701,49781,49862,49942,50023,50103,
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50183,50262,50342,50421,50501,50580,50659,50738,
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50816,50895,50973,51051,51129,51207,51284,51362,
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51439,51517,51594,51670,51747,51824,51900,51977,
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52053,52129,52205,52280,52356,52431,52507,52582,
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46140,46229,46318,46406,46494,46583,46670,46758,
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46846,46933,47020,47107,47193,47280,47366,47452,
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47538,47623,47709,47794,47879,47964,48048,48133,
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48217,48301,48385,48468,48552,48635,48718,48801,
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48884,48966,49048,49131,49213,49294,49376,49458,
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49539,49620,49701,49782,49862,49943,50023,50103,
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50183,50263,50342,50422,50501,50580,50659,50738,
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50816,50895,50973,51051,51129,51207,51285,51362,
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51439,51517,51594,51671,51747,51824,51900,51977,
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52053,52129,52205,52280,52356,52432,52507,52582,
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52657,52732,52807,52881,52956,53030,53104,53178,
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53252,53326,53399,53473,53546,53620,53693,53766,
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53252,53326,53400,53473,53546,53620,53693,53766,
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53839,53911,53984,54056,54129,54201,54273,54345,
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54417,54489,54560,54632,54703,54774,54845,54916,
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54987,55058,55128,55199,55269,55340,55410,55480,
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55550,55619,55689,55759,55828,55897,55967,56036,
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56105,56174,56242,56311,56380,56448,56516,56585,
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54987,55058,55129,55199,55269,55340,55410,55480,
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55550,55620,55689,55759,55828,55898,55967,56036,
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56105,56174,56243,56311,56380,56448,56517,56585,
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56653,56721,56789,56857,56924,56992,57059,57127,
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57194,57261,57328,57395,57462,57529,57595,57662,
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57728,57795,57861,57927,57993,58059,58125,58191,
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@@ -3126,22 +2975,22 @@ PNG_CONST png_uint_16 png_sRGB_base[512] =
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60308,60370,60433,60495,60558,60620,60682,60744,
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60806,60868,60930,60992,61054,61115,61177,61238,
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61300,61361,61422,61483,61544,61605,61666,61727,
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61788,61848,61909,61969,62030,62090,62150,62210,
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61788,61848,61909,61969,62030,62090,62150,62211,
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62271,62331,62391,62450,62510,62570,62630,62689,
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62749,62808,62867,62927,62986,63045,63104,63163,
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63222,63281,63339,63398,63457,63515,63574,63632,
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63222,63281,63340,63398,63457,63515,63574,63632,
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63691,63749,63807,63865,63923,63981,64039,64097,
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64155,64212,64270,64328,64385,64442,64500,64557,
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64614,64671,64729,64786,64843,64899,64956,65013,
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65070,65126,65183,65239,65296,65352,65408,65465
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64155,64212,64270,64328,64385,64443,64500,64557,
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64614,64672,64729,64786,64843,64900,64956,65013,
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65070,65126,65183,65239,65296,65352,65409,65465
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};
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PNG_CONST png_byte png_sRGB_delta[512] =
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{
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207,200,157,129,111,99,90,82,77,72,68,64,61,59,56,54,
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207,201,158,129,113,100,90,82,77,72,68,64,61,59,56,54,
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52,50,49,47,46,45,43,42,41,40,39,39,38,37,36,36,
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35,34,34,33,33,32,32,31,31,30,30,30,29,29,28,28,
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28,27,27,27,26,26,26,26,25,25,25,25,24,24,24,24,
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28,27,27,27,27,26,26,26,25,25,25,25,24,24,24,24,
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23,23,23,23,23,22,22,22,22,22,22,21,21,21,21,21,
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21,20,20,20,20,20,20,20,20,19,19,19,19,19,19,19,
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19,18,18,18,18,18,18,18,18,18,18,17,17,17,17,17,
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@@ -3171,11 +3020,6 @@ PNG_CONST png_byte png_sRGB_delta[512] =
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
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};
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/* Hence the define in pngpriv.h to calculate the sRGB value of a linear value
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* expressed as a fixed point integer scaled by 255*65535 (note that the tables
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* include the +.5 to do rounding correctly.)
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*/
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#endif /* SIMPLIFIED READ/WRITE sRGB support */
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/* SIMPLIFIED READ/WRITE SUPPORT */
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