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Diffstat (limited to 'libpng/contrib/tools/makesRGB.c')
| -rw-r--r-- | libpng/contrib/tools/makesRGB.c | 430 |
1 files changed, 430 insertions, 0 deletions
diff --git a/libpng/contrib/tools/makesRGB.c b/libpng/contrib/tools/makesRGB.c new file mode 100644 index 00000000..e66c9f15 --- /dev/null +++ b/libpng/contrib/tools/makesRGB.c @@ -0,0 +1,430 @@ +/* makesRGB.c -- build sRGB-to-linear and linear-to-sRGB conversion tables + * + * Last changed in libpng 1.6.0 [February 14, 2013] + * + * COPYRIGHT: Written by John Cunningham Bowler, 2013. + * To the extent possible under law, the author has waived all copyright and + * related or neighboring rights to this work. This work is published from: + * United States. + * + * Make a table to convert 8-bit sRGB encoding values into the closest 16-bit + * linear value. + * + * Make two tables to take a linear value scaled to 255*65535 and return an + * approximation to the 8-bit sRGB encoded value. Calculate the error in these + * tables and display it. + */ +#define _C99_SOURCE 1 +#include <stdio.h> +#include <math.h> +#include <stdlib.h> + +/* pngpriv.h includes the definition of 'PNG_sRGB_FROM_LINEAR' which is required + * to verify the actual code. + */ +#include "../../pngpriv.h" + +#include "sRGB.h" + +/* The tables are declared 'const' in pngpriv.h, so this redefines the tables to + * be used. + */ +#define png_sRGB_table sRGB_table +#define png_sRGB_base sRGB_base +#define png_sRGB_delta sRGB_delta + +static png_uint_16 png_sRGB_table[256]; +static png_uint_16 png_sRGB_base[512]; +static png_byte png_sRGB_delta[512]; + +static const unsigned int max_input = 255*65535; + +double +fsRGB(double l) +{ + return sRGB_from_linear(l/max_input); +} + +double +sRGB(unsigned int i) +{ + return fsRGB(i); +} + +double +finvsRGB(unsigned int i) +{ + return 65535 * linear_from_sRGB(i/255.); +} + +png_uint_16 +invsRGB(unsigned int i) +{ + unsigned int x = nearbyint(finvsRGB(i)); + + if (x > 65535) + { + fprintf(stderr, "invsRGB(%u) overflows to %u\n", i, x); + exit(1); + } + + return (png_uint_16)x; +} + +int +main(int argc, char **argv) +{ + unsigned int i, i16, ibase; + double min_error = 0; + double max_error = 0; + double min_error16 = 0; + double max_error16 = 0; + double adjust; + double adjust_lo = 0.4, adjust_hi = 0.6, adjust_mid = 0.5; + unsigned int ec_lo = 0, ec_hi = 0, ec_mid = 0; + unsigned int error_count = 0; + unsigned int error_count16 = 0; + int test_only = 0; + + if (argc > 1) + test_only = strcmp("--test", argv[1]) == 0; + + /* Initialize the encoding table first. */ + for (i=0; i<256; ++i) + { + png_sRGB_table[i] = invsRGB(i); + } + + /* Now work out the decoding tables (this is where the error comes in because + * there are 512 set points and 512 straight lines between them.) + */ + for (;;) + { + if (ec_lo == 0) + adjust = adjust_lo; + + else if (ec_hi == 0) + adjust = adjust_hi; + + else if (ec_mid == 0) + adjust = adjust_mid; + + else if (ec_mid < ec_hi) + adjust = (adjust_mid + adjust_hi)/2; + + else if (ec_mid < ec_lo) + adjust = (adjust_mid + adjust_lo)/2; + + else + { + fprintf(stderr, "not reached: %u .. %u .. %u\n", ec_lo, ec_mid, ec_hi); + exit(1); + } + + /* Calculate the table using the current 'adjust' */ + for (i=0; i<=511; ++i) + { + double lo = 255 * sRGB(i << 15); + double hi = 255 * sRGB((i+1) << 15); + unsigned int calc; + + calc = nearbyint((lo+adjust) * 256); + if (calc > 65535) + { + fprintf(stderr, "table[%d][0]: overflow %08x (%d)\n", i, calc, + calc); + exit(1); + } + png_sRGB_base[i] = calc; + + calc = nearbyint((hi-lo) * 32); + if (calc > 255) + { + fprintf(stderr, "table[%d][1]: overflow %08x (%d)\n", i, calc, + calc); + exit(1); + } + png_sRGB_delta[i] = calc; + } + + /* Check the 16-bit linear values alone: */ + error_count16 = 0; + for (i16=0; i16 <= 65535; ++i16) + { + unsigned int i = 255*i16; + unsigned int iexact = nearbyint(255*sRGB(i)); + unsigned int icalc = PNG_sRGB_FROM_LINEAR(i); + + if (icalc != iexact) + ++error_count16; + } + + /* Now try changing the adjustment. */ + if (ec_lo == 0) + ec_lo = error_count16; + + else if (ec_hi == 0) + ec_hi = error_count16; + + else if (ec_mid == 0) + { + ec_mid = error_count16; + printf("/* initial error counts: %u .. %u .. %u */\n", ec_lo, ec_mid, + ec_hi); + } + + else if (error_count16 < ec_mid) + { + printf("/* adjust (mid ): %f: %u -> %u */\n", adjust, ec_mid, + error_count16); + ec_mid = error_count16; + adjust_mid = adjust; + } + + else if (adjust < adjust_mid && error_count16 < ec_lo) + { + printf("/* adjust (low ): %f: %u -> %u */\n", adjust, ec_lo, + error_count16); + ec_lo = error_count16; + adjust_lo = adjust; + } + + else if (adjust > adjust_mid && error_count16 < ec_hi) + { + printf("/* adjust (high): %f: %u -> %u */\n", adjust, ec_hi, + error_count16); + ec_hi = error_count16; + adjust_hi = adjust; + } + + else + { + adjust = adjust_mid; + printf("/* adjust: %f: %u */\n", adjust, ec_mid); + break; + } + } + + /* For each entry in the table try to adjust it to minimize the error count + * in that entry. Each entry corresponds to 128 input values. + */ + for (ibase=0; ibase<65536; ibase+=128) + { + png_uint_16 base = png_sRGB_base[ibase >> 7], trybase = base, ob=base; + png_byte delta = png_sRGB_delta[ibase >> 7], trydelta = delta, od=delta; + unsigned int ecbase = 0, eco; + + for (;;) + { + png_sRGB_base[ibase >> 7] = trybase; + png_sRGB_delta[ibase >> 7] = trydelta; + + /* Check the 16-bit linear values alone: */ + error_count16 = 0; + for (i16=ibase; i16 < ibase+128; ++i16) + { + unsigned int i = 255*i16; + unsigned int iexact = nearbyint(255*sRGB(i)); + unsigned int icalc = PNG_sRGB_FROM_LINEAR(i); + + if (icalc != iexact) + ++error_count16; + } + + if (error_count16 == 0) + break; + + if (ecbase == 0) + { + eco = ecbase = error_count16; + ++trybase; /* First test */ + } + + else if (error_count16 < ecbase) + { + if (trybase > base) + { + base = trybase; + ++trybase; + } + else if (trybase < base) + { + base = trybase; + --trybase; + } + else if (trydelta > delta) + { + delta = trydelta; + ++trydelta; + } + else if (trydelta < delta) + { + delta = trydelta; + --trydelta; + } + else + { + fprintf(stderr, "makesRGB: impossible\n"); + exit(1); + } + ecbase = error_count16; + } + + else + { + if (trybase > base) + trybase = base-1; + else if (trybase < base) + { + trybase = base; + ++trydelta; + } + else if (trydelta > delta) + trydelta = delta-1; + else if (trydelta < delta) + break; /* end of tests */ + } + } + + png_sRGB_base[ibase >> 7] = base; + png_sRGB_delta[ibase >> 7] = delta; + if (base != ob || delta != od) + { + printf("/* table[%u]={%u,%u} -> {%u,%u} %u -> %u errors */\n", + ibase>>7, ob, od, base, delta, eco, ecbase); + } + else if (0) + printf("/* table[%u]={%u,%u} %u errors */\n", ibase>>7, ob, od, + ecbase); + } + + /* Only do the full (slow) test at the end: */ + min_error = -.4999; + max_error = .4999; + error_count = 0; + + for (i=0; i <= max_input; ++i) + { + unsigned int iexact = nearbyint(255*sRGB(i)); + unsigned int icalc = PNG_sRGB_FROM_LINEAR(i); + + if (icalc != iexact) + { + double err = 255*sRGB(i) - icalc; + + if (err > (max_error+.001) || err < (min_error-.001)) + { + printf( + "/* 0x%08x: exact: %3d, got: %3d [tables: %08x, %08x] (%f) */\n", + i, iexact, icalc, png_sRGB_base[i>>15], + png_sRGB_delta[i>>15], err); + } + + ++error_count; + if (err > max_error) + max_error = err; + else if (err < min_error) + min_error = err; + } + } + + /* Re-check the 16-bit cases too, including the warning if there is an error + * bigger than 1. + */ + error_count16 = 0; + max_error16 = 0; + min_error16 = 0; + for (i16=0; i16 <= 65535; ++i16) + { + unsigned int i = 255*i16; + unsigned int iexact = nearbyint(255*sRGB(i)); + unsigned int icalc = PNG_sRGB_FROM_LINEAR(i); + + if (icalc != iexact) + { + double err = 255*sRGB(i) - icalc; + + ++error_count16; + if (err > max_error16) + max_error16 = err; + else if (err < min_error16) + min_error16 = err; + + if (abs(icalc - iexact) > 1) + printf( + "/* 0x%04x: exact: %3d, got: %3d [tables: %08x, %08x] (%f) */\n", + i16, iexact, icalc, png_sRGB_base[i>>15], + png_sRGB_delta[i>>15], err); + } + } + + /* Check the round trip for each 8-bit sRGB value. */ + for (i16=0; i16 <= 255; ++i16) + { + unsigned int i = 255 * png_sRGB_table[i16]; + unsigned int iexact = nearbyint(255*sRGB(i)); + unsigned int icalc = PNG_sRGB_FROM_LINEAR(i); + + if (i16 != iexact) + { + fprintf(stderr, "8-bit rounding error: %d -> %d\n", i16, iexact); + exit(1); + } + + if (icalc != i16) + { + double finv = finvsRGB(i16); + + printf("/* 8-bit roundtrip error: %d -> %f -> %d(%f) */\n", + i16, finv, icalc, fsRGB(255*finv)); + } + } + + + printf("/* error: %g - %g, %u (%g%%) of readings inexact */\n", + min_error, max_error, error_count, (100.*error_count)/max_input); + printf("/* 16-bit error: %g - %g, %u (%g%%) of readings inexact */\n", + min_error16, max_error16, error_count16, (100.*error_count16)/65535); + + if (!test_only) + { + printf("PNG_CONST png_uint_16 png_sRGB_table[256] =\n{\n "); + for (i=0; i<255; ) + { + do + { + printf("%d,", png_sRGB_table[i++]); + } + while ((i & 0x7) != 0 && i<255); + if (i<255) printf("\n "); + } + printf("%d\n};\n\n", png_sRGB_table[i]); + + + printf("PNG_CONST png_uint_16 png_sRGB_base[512] =\n{\n "); + for (i=0; i<511; ) + { + do + { + printf("%d,", png_sRGB_base[i++]); + } + while ((i & 0x7) != 0 && i<511); + if (i<511) printf("\n "); + } + printf("%d\n};\n\n", png_sRGB_base[i]); + + printf("PNG_CONST png_byte png_sRGB_delta[512] =\n{\n "); + for (i=0; i<511; ) + { + do + { + printf("%d,", png_sRGB_delta[i++]); + } + while ((i & 0xf) != 0 && i<511); + if (i<511) printf("\n "); + } + printf("%d\n};\n\n", png_sRGB_delta[i]); + } + + return 0; +} |