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pngrtran.c
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/* pngrtran.c - transforms the data in a row for PNG readers
*
* Copyright (c) 2018-2024 Cosmin Truta
* Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
* Copyright (c) 1996-1997 Andreas Dilger
* Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
* and license in png.h
*
* This file contains functions optionally called by an application
* in order to tell libpng how to handle data when reading a PNG.
* Transformations that are used in both reading and writing are
* in pngtrans.c.
*/
#include "pngpriv.h"
#ifdef PNG_ARM_NEON_IMPLEMENTATION
# if PNG_ARM_NEON_IMPLEMENTATION == 1
# define PNG_ARM_NEON_INTRINSICS_AVAILABLE
# if defined(_MSC_VER) && !defined(__clang__) && defined(_M_ARM64)
# include <arm64_neon.h>
# else
# include <arm_neon.h>
# endif
# endif
#endif
#ifdef PNG_READ_SUPPORTED
/* Set the action on getting a CRC error for an ancillary or critical chunk. */
void PNGAPI
png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
{
png_debug(1, "in png_set_crc_action");
if (png_ptr == NULL)
return;
/* Tell libpng how we react to CRC errors in critical chunks */
switch (crit_action)
{
case PNG_CRC_NO_CHANGE: /* Leave setting as is */
break;
case PNG_CRC_WARN_USE: /* Warn/use data */
png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
break;
case PNG_CRC_QUIET_USE: /* Quiet/use data */
png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
PNG_FLAG_CRC_CRITICAL_IGNORE;
break;
case PNG_CRC_WARN_DISCARD: /* Not a valid action for critical data */
png_warning(png_ptr,
"Can't discard critical data on CRC error");
/* FALLTHROUGH */
case PNG_CRC_ERROR_QUIT: /* Error/quit */
case PNG_CRC_DEFAULT:
default:
png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
break;
}
/* Tell libpng how we react to CRC errors in ancillary chunks */
switch (ancil_action)
{
case PNG_CRC_NO_CHANGE: /* Leave setting as is */
break;
case PNG_CRC_WARN_USE: /* Warn/use data */
png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
break;
case PNG_CRC_QUIET_USE: /* Quiet/use data */
png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
PNG_FLAG_CRC_ANCILLARY_NOWARN;
break;
case PNG_CRC_ERROR_QUIT: /* Error/quit */
png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
break;
case PNG_CRC_WARN_DISCARD: /* Warn/discard data */
case PNG_CRC_DEFAULT:
default:
png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
break;
}
}
#ifdef PNG_READ_TRANSFORMS_SUPPORTED
/* Is it OK to set a transformation now? Only if png_start_read_image or
* png_read_update_info have not been called. It is not necessary for the IHDR
* to have been read in all cases; the need_IHDR parameter allows for this
* check too.
*/
static int
png_rtran_ok(png_structrp png_ptr, int need_IHDR)
{
if (png_ptr != NULL)
{
if ((png_ptr->flags & PNG_FLAG_ROW_INIT) != 0)
png_app_error(png_ptr,
"invalid after png_start_read_image or png_read_update_info");
else if (need_IHDR && (png_ptr->mode & PNG_HAVE_IHDR) == 0)
png_app_error(png_ptr, "invalid before the PNG header has been read");
else
{
/* Turn on failure to initialize correctly for all transforms. */
png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
return 1; /* Ok */
}
}
return 0; /* no png_error possible! */
}
#endif
#ifdef PNG_READ_BACKGROUND_SUPPORTED
/* Handle alpha and tRNS via a background color */
void PNGFAPI
png_set_background_fixed(png_structrp png_ptr,
png_const_color_16p background_color, int background_gamma_code,
int need_expand, png_fixed_point background_gamma)
{
png_debug(1, "in png_set_background_fixed");
if (png_rtran_ok(png_ptr, 0) == 0 || background_color == NULL)
return;
if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
{
png_warning(png_ptr, "Application must supply a known background gamma");
return;
}
png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
png_ptr->background = *background_color;
png_ptr->background_gamma = background_gamma;
png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
if (need_expand != 0)
png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
else
png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
}
# ifdef PNG_FLOATING_POINT_SUPPORTED
void PNGAPI
png_set_background(png_structrp png_ptr,
png_const_color_16p background_color, int background_gamma_code,
int need_expand, double background_gamma)
{
png_set_background_fixed(png_ptr, background_color, background_gamma_code,
need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
}
# endif /* FLOATING_POINT */
#endif /* READ_BACKGROUND */
/* Scale 16-bit depth files to 8-bit depth. If both of these are set then the
* one that pngrtran does first (scale) happens. This is necessary to allow the
* TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
*/
#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
void PNGAPI
png_set_scale_16(png_structrp png_ptr)
{
png_debug(1, "in png_set_scale_16");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= PNG_SCALE_16_TO_8;
}
#endif
#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
/* Chop 16-bit depth files to 8-bit depth */
void PNGAPI
png_set_strip_16(png_structrp png_ptr)
{
png_debug(1, "in png_set_strip_16");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= PNG_16_TO_8;
}
#endif
#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
void PNGAPI
png_set_strip_alpha(png_structrp png_ptr)
{
png_debug(1, "in png_set_strip_alpha");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= PNG_STRIP_ALPHA;
}
#endif
#if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
/* PNGv3 conformance: this private API exists to resolve the now mandatory error
* resolution when multiple conflicting sources of gamma or colour space
* information are available.
*
* Terminology (assuming power law, "gamma", encodings):
* "screen" gamma: a power law imposed by the output device when digital
* samples are converted to visible light output. The EOTF - volage to
* luminance on output.
*
* "file" gamma: a power law used to encode luminance levels from the input
* data (the scene or the mastering display system) into digital voltages.
* The OETF - luminance to voltage on input.
*
* gamma "correction": a power law matching the **inverse** of the overall
* transfer function from input luminance levels to output levels. The
* **inverse** of the OOTF; the correction "corrects" for the OOTF by aiming
* to make the overall OOTF (including the correction) linear.
*
* It is important to understand this terminology because the defined terms are
* scattered throughout the libpng code and it is very easy to end up with the
* inverse of the power law required.
*
* Variable and struct::member names:
* file_gamma OETF how the PNG data was encoded
*
* screen_gamma EOTF how the screen will decode digital levels
*
* -- not used -- OOTF the net effect OETF x EOTF
* gamma_correction the inverse of OOTF to make the result linear
*
* All versions of libpng require a call to "png_set_gamma" to establish the
* "screen" gamma, the power law representing the EOTF. png_set_gamma may also
* set or default the "file" gamma; the OETF. gamma_correction is calculated
* internally.
*
* The earliest libpng versions required file_gamma to be supplied to set_gamma.
* Later versions started allowing png_set_gamma and, later, png_set_alpha_mode,
* to cause defaulting from the file data.
*
* PNGv3 mandated a particular form for this defaulting, one that is compatible
* with what libpng did except that if libpng detected inconsistencies it marked
* all the chunks as "invalid". PNGv3 effectively invalidates this prior code.
*
* Behaviour implemented below:
* translate_gamma_flags(gamma, is_screen)
* The libpng-1.6 API for the gamma parameters to libpng APIs
* (png_set_gamma and png_set_alpha_mode at present). This allows the
* 'gamma' value to be passed as a png_fixed_point number or as one of a
* set of integral values for specific "well known" examples of transfer
* functions. This is compatible with PNGv3.
*/
static png_fixed_point
translate_gamma_flags(png_fixed_point output_gamma, int is_screen)
{
/* Check for flag values. The main reason for having the old Mac value as a
* flag is that it is pretty near impossible to work out what the correct
* value is from Apple documentation - a working Mac system is needed to
* discover the value!
*/
if (output_gamma == PNG_DEFAULT_sRGB ||
output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
{
if (is_screen != 0)
output_gamma = PNG_GAMMA_sRGB;
else
output_gamma = PNG_GAMMA_sRGB_INVERSE;
}
else if (output_gamma == PNG_GAMMA_MAC_18 ||
output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
{
if (is_screen != 0)
output_gamma = PNG_GAMMA_MAC_OLD;
else
output_gamma = PNG_GAMMA_MAC_INVERSE;
}
return output_gamma;
}
# ifdef PNG_FLOATING_POINT_SUPPORTED
static png_fixed_point
convert_gamma_value(png_structrp png_ptr, double output_gamma)
{
/* The following silently ignores cases where fixed point (times 100,000)
* gamma values are passed to the floating point API. This is safe and it
* means the fixed point constants work just fine with the floating point
* API. The alternative would just lead to undetected errors and spurious
* bug reports. Negative values fail inside the _fixed API unless they
* correspond to the flag values.
*/
if (output_gamma > 0 && output_gamma < 128)
output_gamma *= PNG_FP_1;
/* This preserves -1 and -2 exactly: */
output_gamma = floor(output_gamma + .5);
if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
png_fixed_error(png_ptr, "gamma value");
return (png_fixed_point)output_gamma;
}
# endif
static int
unsupported_gamma(png_structrp png_ptr, png_fixed_point gamma, int warn)
{
/* Validate a gamma value to ensure it is in a reasonable range. The value
* is expected to be 1 or greater, but this range test allows for some
* viewing correction values. The intent is to weed out the API users
* who might use the inverse of the gamma value accidentally!
*
* 1.6.47: apply the test in png_set_gamma as well but only warn and return
* false if it fires.
*
* TODO: 1.8: make this an app_error in png_set_gamma as well.
*/
if (gamma < PNG_LIB_GAMMA_MIN || gamma > PNG_LIB_GAMMA_MAX)
{
# define msg "gamma out of supported range"
if (warn)
png_app_warning(png_ptr, msg);
else
png_app_error(png_ptr, msg);
return 1;
# undef msg
}
return 0;
}
#endif /* READ_ALPHA_MODE || READ_GAMMA */
#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
void PNGFAPI
png_set_alpha_mode_fixed(png_structrp png_ptr, int mode,
png_fixed_point output_gamma)
{
png_fixed_point file_gamma;
int compose = 0;
png_debug(1, "in png_set_alpha_mode_fixed");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
output_gamma = translate_gamma_flags(output_gamma, 1/*screen*/);
if (unsupported_gamma(png_ptr, output_gamma, 0/*error*/))
return;
/* The default file gamma is the inverse of the output gamma; the output
* gamma may be changed below so get the file value first. The default_gamma
* is set here and from the simplified API (which uses a different algorithm)
* so don't overwrite a set value:
*/
file_gamma = png_ptr->default_gamma;
if (file_gamma == 0)
{
file_gamma = png_reciprocal(output_gamma);
png_ptr->default_gamma = file_gamma;
}
/* There are really 8 possibilities here, composed of any combination
* of:
*
* premultiply the color channels
* do not encode non-opaque pixels
* encode the alpha as well as the color channels
*
* The differences disappear if the input/output ('screen') gamma is 1.0,
* because then the encoding is a no-op and there is only the choice of
* premultiplying the color channels or not.
*
* png_set_alpha_mode and png_set_background interact because both use
* png_compose to do the work. Calling both is only useful when
* png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
* with a default gamma value. Otherwise PNG_COMPOSE must not be set.
*/
switch (mode)
{
case PNG_ALPHA_PNG: /* default: png standard */
/* No compose, but it may be set by png_set_background! */
png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
break;
case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
compose = 1;
png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
/* The output is linear: */
output_gamma = PNG_FP_1;
break;
case PNG_ALPHA_OPTIMIZED: /* associated, non-opaque pixels linear */
compose = 1;
png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
/* output_gamma records the encoding of opaque pixels! */
break;
case PNG_ALPHA_BROKEN: /* associated, non-linear, alpha encoded */
compose = 1;
png_ptr->transformations |= PNG_ENCODE_ALPHA;
png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
break;
default:
png_error(png_ptr, "invalid alpha mode");
}
/* Set the screen gamma values: */
png_ptr->screen_gamma = output_gamma;
/* Finally, if pre-multiplying, set the background fields to achieve the
* desired result.
*/
if (compose != 0)
{
/* And obtain alpha pre-multiplication by composing on black: */
memset(&png_ptr->background, 0, (sizeof png_ptr->background));
png_ptr->background_gamma = file_gamma; /* just in case */
png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
if ((png_ptr->transformations & PNG_COMPOSE) != 0)
png_error(png_ptr,
"conflicting calls to set alpha mode and background");
png_ptr->transformations |= PNG_COMPOSE;
}
}
# ifdef PNG_FLOATING_POINT_SUPPORTED
void PNGAPI
png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
{
png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
output_gamma));
}
# endif
#endif
#ifdef PNG_READ_QUANTIZE_SUPPORTED
/* Dither file to 8-bit. Supply a palette, the current number
* of elements in the palette, the maximum number of elements
* allowed, and a histogram if possible. If the current number
* of colors is greater than the maximum number, the palette will be
* modified to fit in the maximum number. "full_quantize" indicates
* whether we need a quantizing cube set up for RGB images, or if we
* simply are reducing the number of colors in a paletted image.
*/
typedef struct png_dsort_struct
{
struct png_dsort_struct * next;
png_byte left;
png_byte right;
} png_dsort;
typedef png_dsort * png_dsortp;
typedef png_dsort * * png_dsortpp;
void PNGAPI
png_set_quantize(png_structrp png_ptr, png_colorp palette,
int num_palette, int maximum_colors, png_const_uint_16p histogram,
int full_quantize)
{
png_debug(1, "in png_set_quantize");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= PNG_QUANTIZE;
if (full_quantize == 0)
{
int i;
png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
(png_alloc_size_t)num_palette);
for (i = 0; i < num_palette; i++)
png_ptr->quantize_index[i] = (png_byte)i;
}
if (num_palette > maximum_colors)
{
if (histogram != NULL)
{
/* This is easy enough, just throw out the least used colors.
* Perhaps not the best solution, but good enough.
*/
int i;
/* Initialize an array to sort colors */
png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
(png_alloc_size_t)num_palette);
/* Initialize the quantize_sort array */
for (i = 0; i < num_palette; i++)
png_ptr->quantize_sort[i] = (png_byte)i;
/* Find the least used palette entries by starting a
* bubble sort, and running it until we have sorted
* out enough colors. Note that we don't care about
* sorting all the colors, just finding which are
* least used.
*/
for (i = num_palette - 1; i >= maximum_colors; i--)
{
int done; /* To stop early if the list is pre-sorted */
int j;
done = 1;
for (j = 0; j < i; j++)
{
if (histogram[png_ptr->quantize_sort[j]]
< histogram[png_ptr->quantize_sort[j + 1]])
{
png_byte t;
t = png_ptr->quantize_sort[j];
png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
png_ptr->quantize_sort[j + 1] = t;
done = 0;
}
}
if (done != 0)
break;
}
/* Swap the palette around, and set up a table, if necessary */
if (full_quantize != 0)
{
int j = num_palette;
/* Put all the useful colors within the max, but don't
* move the others.
*/
for (i = 0; i < maximum_colors; i++)
{
if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
{
do
j--;
while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
palette[i] = palette[j];
}
}
}
else
{
int j = num_palette;
/* Move all the used colors inside the max limit, and
* develop a translation table.
*/
for (i = 0; i < maximum_colors; i++)
{
/* Only move the colors we need to */
if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
{
png_color tmp_color;
do
j--;
while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
tmp_color = palette[j];
palette[j] = palette[i];
palette[i] = tmp_color;
/* Indicate where the color went */
png_ptr->quantize_index[j] = (png_byte)i;
png_ptr->quantize_index[i] = (png_byte)j;
}
}
/* Find closest color for those colors we are not using */
for (i = 0; i < num_palette; i++)
{
if ((int)png_ptr->quantize_index[i] >= maximum_colors)
{
int min_d, k, min_k, d_index;
/* Find the closest color to one we threw out */
d_index = png_ptr->quantize_index[i];
min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
for (k = 1, min_k = 0; k < maximum_colors; k++)
{
int d;
d = PNG_COLOR_DIST(palette[d_index], palette[k]);
if (d < min_d)
{
min_d = d;
min_k = k;
}
}
/* Point to closest color */
png_ptr->quantize_index[i] = (png_byte)min_k;
}
}
}
png_free(png_ptr, png_ptr->quantize_sort);
png_ptr->quantize_sort = NULL;
}
else
{
/* This is much harder to do simply (and quickly). Perhaps
* we need to go through a median cut routine, but those
* don't always behave themselves with only a few colors
* as input. So we will just find the closest two colors,
* and throw out one of them (chosen somewhat randomly).
* [We don't understand this at all, so if someone wants to
* work on improving it, be our guest - AED, GRP]
*/
int i;
int max_d;
int num_new_palette;
png_dsortp t;
png_dsortpp hash;
t = NULL;
/* Initialize palette index arrays */
png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
(png_alloc_size_t)num_palette);
png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
(png_alloc_size_t)num_palette);
/* Initialize the sort array */
for (i = 0; i < num_palette; i++)
{
png_ptr->index_to_palette[i] = (png_byte)i;
png_ptr->palette_to_index[i] = (png_byte)i;
}
hash = (png_dsortpp)png_calloc(png_ptr, (png_alloc_size_t)(769 *
(sizeof (png_dsortp))));
num_new_palette = num_palette;
/* Initial wild guess at how far apart the farthest pixel
* pair we will be eliminating will be. Larger
* numbers mean more areas will be allocated, Smaller
* numbers run the risk of not saving enough data, and
* having to do this all over again.
*
* I have not done extensive checking on this number.
*/
max_d = 96;
while (num_new_palette > maximum_colors)
{
for (i = 0; i < num_new_palette - 1; i++)
{
int j;
for (j = i + 1; j < num_new_palette; j++)
{
int d;
d = PNG_COLOR_DIST(palette[i], palette[j]);
if (d <= max_d)
{
t = (png_dsortp)png_malloc_warn(png_ptr,
(png_alloc_size_t)(sizeof (png_dsort)));
if (t == NULL)
break;
t->next = hash[d];
t->left = (png_byte)i;
t->right = (png_byte)j;
hash[d] = t;
}
}
if (t == NULL)
break;
}
if (t != NULL)
for (i = 0; i <= max_d; i++)
{
if (hash[i] != NULL)
{
png_dsortp p;
for (p = hash[i]; p; p = p->next)
{
if ((int)png_ptr->index_to_palette[p->left]
< num_new_palette &&
(int)png_ptr->index_to_palette[p->right]
< num_new_palette)
{
int j, next_j;
if (num_new_palette & 0x01)
{
j = p->left;
next_j = p->right;
}
else
{
j = p->right;
next_j = p->left;
}
num_new_palette--;
palette[png_ptr->index_to_palette[j]]
= palette[num_new_palette];
if (full_quantize == 0)
{
int k;
for (k = 0; k < num_palette; k++)
{
if (png_ptr->quantize_index[k] ==
png_ptr->index_to_palette[j])
png_ptr->quantize_index[k] =
png_ptr->index_to_palette[next_j];
if ((int)png_ptr->quantize_index[k] ==
num_new_palette)
png_ptr->quantize_index[k] =
png_ptr->index_to_palette[j];
}
}
png_ptr->index_to_palette[png_ptr->palette_to_index
[num_new_palette]] = png_ptr->index_to_palette[j];
png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
= png_ptr->palette_to_index[num_new_palette];
png_ptr->index_to_palette[j] =
(png_byte)num_new_palette;
png_ptr->palette_to_index[num_new_palette] =
(png_byte)j;
}
if (num_new_palette <= maximum_colors)
break;
}
if (num_new_palette <= maximum_colors)
break;
}
}
for (i = 0; i < 769; i++)
{
if (hash[i] != NULL)
{
png_dsortp p = hash[i];
while (p)
{
t = p->next;
png_free(png_ptr, p);
p = t;
}
}
hash[i] = 0;
}
max_d += 96;
}
png_free(png_ptr, hash);
png_free(png_ptr, png_ptr->palette_to_index);
png_free(png_ptr, png_ptr->index_to_palette);
png_ptr->palette_to_index = NULL;
png_ptr->index_to_palette = NULL;
}
num_palette = maximum_colors;
}
if (png_ptr->palette == NULL)
{
png_ptr->palette = palette;
}
png_ptr->num_palette = (png_uint_16)num_palette;
if (full_quantize != 0)
{
int i;
png_bytep distance;
int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
PNG_QUANTIZE_BLUE_BITS;
int num_red = (1 << PNG_QUANTIZE_RED_BITS);
int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
size_t num_entries = ((size_t)1 << total_bits);
png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
(png_alloc_size_t)(num_entries));
distance = (png_bytep)png_malloc(png_ptr, (png_alloc_size_t)num_entries);
memset(distance, 0xff, num_entries);
for (i = 0; i < num_palette; i++)
{
int ir, ig, ib;
int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));
for (ir = 0; ir < num_red; ir++)
{
/* int dr = abs(ir - r); */
int dr = ((ir > r) ? ir - r : r - ir);
int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
PNG_QUANTIZE_GREEN_BITS));
for (ig = 0; ig < num_green; ig++)
{
/* int dg = abs(ig - g); */
int dg = ((ig > g) ? ig - g : g - ig);
int dt = dr + dg;
int dm = ((dr > dg) ? dr : dg);
int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);
for (ib = 0; ib < num_blue; ib++)
{
int d_index = index_g | ib;
/* int db = abs(ib - b); */
int db = ((ib > b) ? ib - b : b - ib);
int dmax = ((dm > db) ? dm : db);
int d = dmax + dt + db;
if (d < (int)distance[d_index])
{
distance[d_index] = (png_byte)d;
png_ptr->palette_lookup[d_index] = (png_byte)i;
}
}
}
}
}
png_free(png_ptr, distance);
}
}
#endif /* READ_QUANTIZE */
#ifdef PNG_READ_GAMMA_SUPPORTED
void PNGFAPI
png_set_gamma_fixed(png_structrp png_ptr, png_fixed_point scrn_gamma,
png_fixed_point file_gamma)
{
png_debug(1, "in png_set_gamma_fixed");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
/* New in libpng-1.5.4 - reserve particular negative values as flags. */
scrn_gamma = translate_gamma_flags(scrn_gamma, 1/*screen*/);
file_gamma = translate_gamma_flags(file_gamma, 0/*file*/);
/* Checking the gamma values for being >0 was added in 1.5.4 along with the
* premultiplied alpha support; this actually hides an undocumented feature
* of the previous implementation which allowed gamma processing to be
* disabled in background handling. There is no evidence (so far) that this
* was being used; however, png_set_background itself accepted and must still
* accept '0' for the gamma value it takes, because it isn't always used.
*
* Since this is an API change (albeit a very minor one that removes an
* undocumented API feature) the following checks were only enabled in
* libpng-1.6.0.
*/
if (file_gamma <= 0)
png_app_error(png_ptr, "invalid file gamma in png_set_gamma");
if (scrn_gamma <= 0)
png_app_error(png_ptr, "invalid screen gamma in png_set_gamma");
if (unsupported_gamma(png_ptr, file_gamma, 1/*warn*/) ||
unsupported_gamma(png_ptr, scrn_gamma, 1/*warn*/))
return;
/* 1.6.47: png_struct::file_gamma and png_struct::screen_gamma are now only
* written by this API. This removes dependencies on the order of API calls
* and allows the complex gamma checks to be delayed until needed.
*/
png_ptr->file_gamma = file_gamma;
png_ptr->screen_gamma = scrn_gamma;
}
# ifdef PNG_FLOATING_POINT_SUPPORTED
void PNGAPI
png_set_gamma(png_structrp png_ptr, double scrn_gamma, double file_gamma)
{
png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
convert_gamma_value(png_ptr, file_gamma));
}
# endif /* FLOATING_POINT */
#endif /* READ_GAMMA */
#ifdef PNG_READ_EXPAND_SUPPORTED
/* Expand paletted images to RGB, expand grayscale images of
* less than 8-bit depth to 8-bit depth, and expand tRNS chunks
* to alpha channels.
*/
void PNGAPI
png_set_expand(png_structrp png_ptr)
{
png_debug(1, "in png_set_expand");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
}
/* GRR 19990627: the following three functions currently are identical
* to png_set_expand(). However, it is entirely reasonable that someone
* might wish to expand an indexed image to RGB but *not* expand a single,
* fully transparent palette entry to a full alpha channel--perhaps instead
* convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
* the transparent color with a particular RGB value, or drop tRNS entirely.
* IOW, a future version of the library may make the transformations flag
* a bit more fine-grained, with separate bits for each of these three
* functions.
*
* More to the point, these functions make it obvious what libpng will be
* doing, whereas "expand" can (and does) mean any number of things.
*
* GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
* to expand only the sample depth but not to expand the tRNS to alpha
* and its name was changed to png_set_expand_gray_1_2_4_to_8().
*/
/* Expand paletted images to RGB. */
void PNGAPI
png_set_palette_to_rgb(png_structrp png_ptr)
{
png_debug(1, "in png_set_palette_to_rgb");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
}
/* Expand grayscale images of less than 8-bit depth to 8 bits. */
void PNGAPI
png_set_expand_gray_1_2_4_to_8(png_structrp png_ptr)
{
png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= PNG_EXPAND;
}
/* Expand tRNS chunks to alpha channels. */
void PNGAPI
png_set_tRNS_to_alpha(png_structrp png_ptr)
{
png_debug(1, "in png_set_tRNS_to_alpha");
if (png_rtran_ok(png_ptr, 0) == 0)
return;
png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
}
#endif /* READ_EXPAND */
#ifdef PNG_READ_EXPAND_16_SUPPORTED
/* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
* it may not work correctly.)
*/
void PNGAPI
png_set_expand_16(png_structrp png_ptr)
{
png_debug(1, "in png_set_expand_16");
if (png_rtran_ok(png_ptr, 0) == 0)