/*
* opngreduc.c - libpng extension: lossless image reductions.
*
* Copyright (C) 2003-2011 Cosmin Truta.
* This software is distributed under the same licensing and warranty terms
* as libpng.
*/
/* CAUTION:
* Image reductions do not work well under certain transformations.
*
* Transformations like PNG_BGR, PNG_SWAP_BYTES, PNG_FILLER, PNG_INVERT_ALPHA,
* and possibly others, require special treatment. However, the libpng API
* does not currently convey the effect of transformations on its internal
* state or on the layout of pixel data.
*
* Transformations which affect pixel depth (e.g. PNG_FILLER) are especially
* dangerous when used in conjunction with this code, and should be avoided.
*/
#include "opngreduc.h"
#ifndef OPNG_ASSERT
#include <assert.h>
#define OPNG_ASSERT(cond) assert(cond)
#define OPNG_ASSERT_MSG(cond, msg) assert(cond)
#endif
#ifdef png_debug
#define opng_debug(level, msg) png_debug(level, msg)
#else
#define opng_debug(level, msg) ((void)0)
#endif
#ifdef PNG_INFO_IMAGE_SUPPORTED
/*
* Check if the image information is valid.
* The image information is said to be valid if all the required
* critical chunk data is present in the png structures.
* The function returns 1 if this information is valid, and 0 otherwise.
*/
int PNGAPI
opng_validate_image(png_structp png_ptr, png_infop info_ptr)
{
opng_debug(1, "in opng_validate_image");
/* Validate IHDR. */
if (png_get_bit_depth(png_ptr, info_ptr) == 0)
return 0;
/* Validate PLTE. */
if (png_get_color_type(png_ptr, info_ptr) & PNG_COLOR_MASK_PALETTE)
{
if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_PLTE))
return 0;
}
/* Validate IDAT. */
if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_IDAT))
return 0;
return 1;
}
#endif /* PNG_INFO_IMAGE_SUPPORTED */
#ifdef OPNG_IMAGE_REDUCTIONS_SUPPORTED
#define OPNG_CMP_RGB(R1, G1, B1, R2, G2, B2) \
(((int)(R1) != (int)(R2)) ? \
((int)(R1) - (int)(R2)) : \
(((int)(G1) != (int)(G2)) ? \
((int)(G1) - (int)(G2)) : \
((int)(B1) - (int)(B2))))
#define OPNG_CMP_ARGB(A1, R1, G1, B1, A2, R2, G2, B2) \
(((int)(A1) != (int)(A2)) ? \
((int)(A1) - (int)(A2)) : \
(((int)(R1) != (R2)) ? \
((int)(R1) - (int)(R2)) : \
(((int)(G1) != (int)(G2)) ? \
((int)(G1) - (int)(G2)) : \
((int)(B1) - (int)(B2)))))
/*
* Build a color+alpha palette in which the entries are sorted by
* (alpha, red, green, blue), in this particular order.
* Use the insertion sort algorithm.
* The alpha value is ignored if it is not in the range [0 .. 255].
* The function returns:
* 1 if the insertion is successful; *index = position of new entry.
* 0 if the insertion is unnecessary; *index = position of crt entry.
* -1 if overflow; *num_palette = *num_trans = *index = -1.
*/
static int /* PRIVATE */
opng_insert_palette_entry(png_colorp palette, int *num_palette,
png_bytep trans_alpha, int *num_trans, int max_tuples,
unsigned int red, unsigned int green, unsigned int blue, unsigned int alpha,
int *index)
{
int low, high, mid, cmp;
int i;
OPNG_ASSERT(*num_palette >= 0 && *num_palette <= max_tuples);
OPNG_ASSERT(*num_trans >= 0 && *num_trans <= *num_palette);
if (alpha < 255)
{
/* Do a binary search among transparent tuples. */
low = 0;
high = *num_trans - 1;
while (low <= high)
{
mid = (low + high) / 2;
cmp = OPNG_CMP_ARGB(alpha, red, green, blue,
trans_alpha[mid],
palette[mid].red, palette[mid].green, palette[mid].blue);
if (cmp < 0)
high = mid - 1;
else if (cmp > 0)
low = mid + 1;
else
{
*index = mid;
return 0;
}
}
}
else /* alpha == 255 || alpha not in [0 .. 255] */
{
/* Do a (faster) binary search among opaque tuples. */
low = *num_trans;
high = *num_palette - 1;
while (low <= high)
{
mid = (low + high) / 2;
cmp = OPNG_CMP_RGB(red, green, blue,
palette[mid].red, palette[mid].green, palette[mid].blue);
if (cmp < 0)
high = mid - 1;
else if (cmp > 0)
low = mid + 1;
else
{
*index = mid;
return 0;
}
}
}
if (alpha > 255)
{
/* The binary search among opaque tuples has failed. */
/* Do a linear search among transparent tuples, ignoring alpha. */
for (i = 0; i < *num_trans; ++i)
{
cmp = OPNG_CMP_RGB(red, green, blue,
palette[i].red, palette[i].green, palette[i].blue);
if (cmp == 0)
{
*index = i;
return 0;
}
}
}
/* Check for overflow. */
if (*num_palette >= max_tuples)
{
*num_palette = *num_trans = *index = -1;
return -1;
}
/* Insert new tuple at [low]. */
OPNG_ASSERT(low >= 0 && low <= *num_palette);
for (i = *num_palette; i > low; --i)
palette[i] = palette[i - 1];
palette[low].red = (png_byte)red;
palette[low].green = (png_byte)green;
palette[low].blue = (png_byte)blue;
++(*num_palette);
if (alpha < 255)
{
OPNG_ASSERT(low <= *num_trans);
for (i = *num_trans; i > low; --i)
trans_alpha[i] = trans_alpha[i - 1];
trans_alpha[low] = (png_byte)alpha;
++(*num_trans);
}
*index = low;
return 1;
}
/*
* Retrieve the alpha samples from the given image row.
*/
static void /* PRIVATE */
opng_get_alpha_row(png_row_infop row_info_ptr, png_color_16p trans_color,
png_bytep row, png_bytep alpha_row)
{
png_bytep sample_ptr;
png_uint_32 width;
int color_type, bit_depth, channels;
png_byte trans_red, trans_green, trans_blue, trans_gray;
png_uint_32 i;
width = row_info_ptr->width;
color_type = row_info_ptr->color_type;
bit_depth = row_info_ptr->bit_depth;
channels = row_info_ptr->channels;
OPNG_ASSERT(!(color_type & PNG_COLOR_MASK_PALETTE));
OPNG_ASSERT(bit_depth == 8);
if (!(color_type & PNG_COLOR_MASK_ALPHA))
{
if (trans_color == NULL)
{
/* All pixels are fully opaque. */
memset(alpha_row, 255, (size_t)width);
return;
}
if (color_type == PNG_COLOR_TYPE_RGB)
{
OPNG_ASSERT(channels == 3);
trans_red = (png_byte)trans_color->red;
trans_green = (png_byte)trans_color->green;
trans_blue = (png_byte)trans_color->blue;
sample_ptr = row;
for (i = 0; i < width; ++i, sample_ptr += 3)
alpha_row[i] = (png_byte)
((sample_ptr[0] == trans_red &&
sample_ptr[1] == trans_green &&
sample_ptr[2] == trans_blue) ? 0 : 255);
}
else
{
OPNG_ASSERT(color_type == PNG_COLOR_TYPE_GRAY);
OPNG_ASSERT(channels == 1);
trans_gray = (png_byte)trans_color->gray;
for (i = 0; i < width; ++i)
alpha_row[i] = (png_byte)((row[i] == trans_gray) ? 0 : 255);
}
return;
}
/* There is a real alpha channel. The alpha sample is last in RGBA tuple. */
OPNG_ASSERT(channels > 1);
sample_ptr = row + (channels - 1);
for (i = 0; i < width; ++i, sample_ptr += channels, ++alpha_row)
*alpha_row = *sample_ptr;
}
/*
* Analyze the redundancy of bits inside the image.
* The parameter reductions indicates the intended reductions.
* The function returns the possible reductions.
*/
static png_uint_32 /* PRIVATE */
opng_analyze_bits(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_bytepp row_ptr;
png_bytep component_ptr;
png_uint_32 height, width;
int bit_depth, color_type, byte_depth, channels, sample_size, offset_alpha;
#ifdef PNG_bKGD_SUPPORTED
png_color_16p background;
#endif
png_uint_32 i, j;
opng_debug(1, "in opng_analyze_bits");
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
NULL, NULL, NULL);
if (bit_depth < 8)
return OPNG_REDUCE_NONE; /* not applicable */
if (color_type & PNG_COLOR_MASK_PALETTE)
return OPNG_REDUCE_NONE; /* let opng_reduce_palette() handle it */
byte_depth = bit_depth / 8;
channels = png_get_channels(png_ptr, info_ptr);
sample_size = channels * byte_depth;
offset_alpha = (channels - 1) * byte_depth;
/* Select the applicable reductions. */
reductions &= (OPNG_REDUCE_16_TO_8 |
OPNG_REDUCE_RGB_TO_GRAY | OPNG_REDUCE_STRIP_ALPHA);
if (bit_depth <= 8)
reductions &= ~OPNG_REDUCE_16_TO_8;
if (!(color_type & PNG_COLOR_MASK_COLOR))
reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
if (!(color_type & PNG_COLOR_MASK_ALPHA))
reductions &= ~OPNG_REDUCE_STRIP_ALPHA;
/* Check if the ancillary information allows these reductions. */
#ifdef PNG_bKGD_SUPPORTED
if (png_get_bKGD(png_ptr, info_ptr, &background))
{
if (reductions & OPNG_REDUCE_16_TO_8)
{
if (background->red % 257 != 0 ||
background->green % 257 != 0 ||
background->blue % 257 != 0 ||
background->gray % 257 != 0)
reductions &= ~OPNG_REDUCE_16_TO_8;
}
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
{
if (background->red != background->green ||
background->red != background->blue)
reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
}
}
#endif
/* Check for each possible reduction, row by row. */
row_ptr = png_get_rows(png_ptr, info_ptr);
for (i = 0; i < height; ++i, ++row_ptr)
{
if (reductions == OPNG_REDUCE_NONE)
return OPNG_REDUCE_NONE; /* no need to go any further */
/* Check if it is possible to reduce the bit depth to 8. */
if (reductions & OPNG_REDUCE_16_TO_8)
{
component_ptr = *row_ptr;
for (j = 0; j < channels * width; ++j, component_ptr += 2)
{
if (component_ptr[0] != component_ptr[1])
{
reductions &= ~OPNG_REDUCE_16_TO_8;
break;
}
}
}
if (bit_depth == 8)
{
/* Check if it is possible to reduce rgb --> gray. */
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
{
component_ptr = *row_ptr;
for (j = 0; j < width; ++j, component_ptr += sample_size)
{
if (component_ptr[0] != component_ptr[1] ||
component_ptr[0] != component_ptr[2])
{
reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
break;
}
}
}
/* Check if it is possible to strip the alpha channel. */
if (reductions & OPNG_REDUCE_STRIP_ALPHA)
{
component_ptr = *row_ptr + offset_alpha;
for (j = 0; j < width; ++j, component_ptr += sample_size)
{
if (component_ptr[0] != 255)
{
reductions &= ~OPNG_REDUCE_STRIP_ALPHA;
break;
}
}
}
}
else /* bit_depth == 16 */
{
/* Check if it is possible to reduce rgb --> gray. */
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
{
component_ptr = *row_ptr;
for (j = 0; j < width; ++j, component_ptr += sample_size)
{
if (component_ptr[0] != component_ptr[2] ||
component_ptr[0] != component_ptr[4] ||
component_ptr[1] != component_ptr[3] ||
component_ptr[1] != component_ptr[5])
{
reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
break;
}
}
}
/* Check if it is possible to strip the alpha channel. */
if (reductions & OPNG_REDUCE_STRIP_ALPHA)
{
component_ptr = *row_ptr + offset_alpha;
for (j = 0; j < width; ++j, component_ptr += sample_size)
{
if (component_ptr[0] != 255 || component_ptr[1] != 255)
{
reductions &= ~OPNG_REDUCE_STRIP_ALPHA;
break;
}
}
}
}
}
return reductions;
}
/*
* Reduce the image type to a lower bit depth and color type,
* by removing redundant bits.
* Possible reductions: 16bpp to 8bpp; RGB to gray; strip alpha.
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
* All reductions are performed in a single step.
*/
static png_uint_32 /* PRIVATE */
opng_reduce_bits(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_bytepp row_ptr;
png_bytep src_ptr, dest_ptr;
png_uint_32 width, height;
int interlace_type, compression_type, filter_type;
int src_bit_depth, dest_bit_depth;
int src_byte_depth, dest_byte_depth;
int src_color_type, dest_color_type;
int src_channels, dest_channels;
int src_sample_size, dest_sample_size;
int tran_tbl[8];
png_color_16p trans_color;
#ifdef PNG_bKGD_SUPPORTED
png_color_16p background;
#endif
#ifdef PNG_sBIT_SUPPORTED
png_color_8p sig_bits;
#endif
png_uint_32 i, j;
int k;
opng_debug(1, "in opng_reduce_bits");
/* See which reductions may be performed. */
reductions = opng_analyze_bits(png_ptr, info_ptr, reductions);
if (reductions == OPNG_REDUCE_NONE)
return OPNG_REDUCE_NONE; /* exit early */
png_get_IHDR(png_ptr, info_ptr, &width, &height,
&src_bit_depth, &src_color_type,
&interlace_type, &compression_type, &filter_type);
/* Compute the new image parameters bit_depth, color_type, etc. */
OPNG_ASSERT(src_bit_depth >= 8);
if (reductions & OPNG_REDUCE_16_TO_8)
{
OPNG_ASSERT(src_bit_depth == 16);
dest_bit_depth = 8;
}
else
dest_bit_depth = src_bit_depth;
src_byte_depth = src_bit_depth / 8;
dest_byte_depth = dest_bit_depth / 8;
dest_color_type = src_color_type;
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
{
OPNG_ASSERT(src_color_type & PNG_COLOR_MASK_COLOR);
dest_color_type &= ~PNG_COLOR_MASK_COLOR;
}
if (reductions & OPNG_REDUCE_STRIP_ALPHA)
{
OPNG_ASSERT(src_color_type & PNG_COLOR_MASK_ALPHA);
dest_color_type &= ~PNG_COLOR_MASK_ALPHA;
}
src_channels = png_get_channels(png_ptr, info_ptr);
dest_channels =
((dest_color_type & PNG_COLOR_MASK_COLOR) ? 3 : 1) +
((dest_color_type & PNG_COLOR_MASK_ALPHA) ? 1 : 0);
src_sample_size = src_channels * src_byte_depth;
dest_sample_size = dest_channels * dest_byte_depth;
/* Pre-compute the intra-sample translation table. */
for (k = 0; k < 4 * dest_byte_depth; ++k)
tran_tbl[k] = k * src_bit_depth / dest_bit_depth;
/* If rgb --> gray, shift the alpha component two positions to the left. */
if ((reductions & OPNG_REDUCE_RGB_TO_GRAY) &&
(dest_color_type & PNG_COLOR_MASK_ALPHA))
{
tran_tbl[dest_byte_depth] = tran_tbl[3 * dest_byte_depth];
if (dest_byte_depth == 2)
tran_tbl[dest_byte_depth + 1] = tran_tbl[3 * dest_byte_depth + 1];
}
/* Translate the samples to the new image type. */
OPNG_ASSERT(src_sample_size > dest_sample_size);
row_ptr = png_get_rows(png_ptr, info_ptr);
for (i = 0; i < height; ++i, ++row_ptr)
{
src_ptr = dest_ptr = *row_ptr;
for (j = 0; j < width; ++j)
{
for (k = 0; k < dest_sample_size; ++k)
dest_ptr[k] = src_ptr[tran_tbl[k]];
src_ptr += src_sample_size;
dest_ptr += dest_sample_size;
}
}
/* Update the ancillary information. */
if (png_get_tRNS(png_ptr, info_ptr, NULL, NULL, &trans_color))
{
if (reductions & OPNG_REDUCE_16_TO_8)
{
if (trans_color->red % 257 == 0 &&
trans_color->green % 257 == 0 &&
trans_color->blue % 257 == 0 &&
trans_color->gray % 257 == 0)
{
trans_color->red &= 255;
trans_color->green &= 255;
trans_color->blue &= 255;
trans_color->gray &= 255;
}
else
{
/* 16-bit tRNS in 8-bit samples: all pixels are 100% opaque. */
png_free_data(png_ptr, info_ptr, PNG_FREE_TRNS, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_tRNS);
}
}
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
{
if (trans_color->red == trans_color->green ||
trans_color->red == trans_color->blue)
trans_color->gray = trans_color->red;
else
{
/* Non-gray tRNS in grayscale image: all pixels are 100% opaque. */
png_free_data(png_ptr, info_ptr, PNG_FREE_TRNS, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_tRNS);
}
}
}
#ifdef PNG_bKGD_SUPPORTED
if (png_get_bKGD(png_ptr, info_ptr, &background))
{
if (reductions & OPNG_REDUCE_16_TO_8)
{
background->red &= 255;
background->green &= 255;
background->blue &= 255;
background->gray &= 255;
}
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
background->gray = background->red;
}
#endif
#ifdef PNG_sBIT_SUPPORTED
if (png_get_sBIT(png_ptr, info_ptr, &sig_bits))
{
if (reductions & OPNG_REDUCE_16_TO_8)
{
if (sig_bits->red > 8)
sig_bits->red = 8;
if (sig_bits->green > 8)
sig_bits->green = 8;
if (sig_bits->blue > 8)
sig_bits->blue = 8;
if (sig_bits->gray > 8)
sig_bits->gray = 8;
if (sig_bits->alpha > 8)
sig_bits->alpha = 8;
}
if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
{
png_byte max_sig_bits = sig_bits->red;
if (max_sig_bits < sig_bits->green)
max_sig_bits = sig_bits->green;
if (max_sig_bits < sig_bits->blue)
max_sig_bits = sig_bits->blue;
sig_bits->gray = max_sig_bits;
}
}
#endif
/* Update the image information. */
png_set_IHDR(png_ptr, info_ptr, width, height,
dest_bit_depth, dest_color_type,
interlace_type, compression_type, filter_type);
return reductions;
}
/*
* Reduce the bit depth of a palette image to the lowest possible value.
* The parameter reductions should contain OPNG_REDUCE_8_TO_4_2_1.
* The function returns OPNG_REDUCE_8_TO_4_2_1 if successful.
*/
static png_uint_32 /* PRIVATE */
opng_reduce_palette_bits(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_bytepp row_ptr;
png_bytep src_sample_ptr, dest_sample_ptr;
png_uint_32 width, height;
int color_type, interlace_type, compression_type, filter_type;
int src_bit_depth, dest_bit_depth;
unsigned int src_mask_init, src_mask, src_shift, dest_shift;
unsigned int sample, dest_buf;
png_colorp palette;
int num_palette;
png_uint_32 i, j;
opng_debug(1, "in opng_reduce_palette_bits");
/* Check if the reduction applies. */
if (!(reductions & OPNG_REDUCE_8_TO_4_2_1))
return OPNG_REDUCE_NONE;
png_get_IHDR(png_ptr, info_ptr, &width, &height, &src_bit_depth,
&color_type, &interlace_type, &compression_type, &filter_type);
if (color_type != PNG_COLOR_TYPE_PALETTE)
return OPNG_REDUCE_NONE;
if (!png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette))
num_palette = 0;
/* Find the smallest possible bit depth. */
if (num_palette > 16)
return OPNG_REDUCE_NONE;
else if (num_palette > 4) /* 5 .. 16 entries */
dest_bit_depth = 4;
else if (num_palette > 2) /* 3 or 4 entries */
dest_bit_depth = 2;
else /* 1 or 2 entries */
{
OPNG_ASSERT(num_palette > 0);
dest_bit_depth = 1;
}
if (src_bit_depth <= dest_bit_depth)
{
OPNG_ASSERT(src_bit_depth == dest_bit_depth);
return OPNG_REDUCE_NONE;
}
/* Iterate through all sample values. */
row_ptr = png_get_rows(png_ptr, info_ptr);
if (src_bit_depth == 8)
{
for (i = 0; i < height; ++i, ++row_ptr)
{
src_sample_ptr = dest_sample_ptr = *row_ptr;
dest_shift = 8;
dest_buf = 0;
for (j = 0; j < width; ++j)
{
dest_shift -= dest_bit_depth;
if (dest_shift > 0)
dest_buf |= *src_sample_ptr << dest_shift;
else
{
*dest_sample_ptr++ = (png_byte)(dest_buf | *src_sample_ptr);
dest_shift = 8;
dest_buf = 0;
}
++src_sample_ptr;
}
if (dest_shift != 0)
*dest_sample_ptr = (png_byte)dest_buf;
}
}
else /* src_bit_depth < 8 */
{
src_mask_init = (1 << (8 + src_bit_depth)) - (1 << 8);
for (i = 0; i < height; ++i, ++row_ptr)
{
src_sample_ptr = dest_sample_ptr = *row_ptr;
src_shift = dest_shift = 8;
src_mask = src_mask_init;
dest_buf = 0;
for (j = 0; j < width; ++j)
{
src_shift -= src_bit_depth;
src_mask >>= src_bit_depth;
sample = (*src_sample_ptr & src_mask) >> src_shift;
dest_shift -= dest_bit_depth;
if (dest_shift > 0)
dest_buf |= sample << dest_shift;
else
{
*dest_sample_ptr++ = (png_byte)(dest_buf | sample);
dest_shift = 8;
dest_buf = 0;
}
if (src_shift == 0)
{
src_shift = 8;
src_mask = src_mask_init;
++src_sample_ptr;
}
}
if (dest_shift != 0)
*dest_sample_ptr = (png_byte)dest_buf;
}
}
/* Update the image information. */
png_set_IHDR(png_ptr, info_ptr, width, height, dest_bit_depth,
color_type, interlace_type, compression_type, filter_type);
return OPNG_REDUCE_8_TO_4_2_1;
}
/*
* Reduce the image type from grayscale(+alpha) or RGB(+alpha) to palette,
* if possible.
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
static png_uint_32 /* PRIVATE */
opng_reduce_to_palette(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_uint_32 result;
png_row_info row_info;
png_bytepp row_ptr;
png_bytep sample_ptr, alpha_row;
png_uint_32 height, width;
int color_type, interlace_type, compression_type, filter_type;
int src_bit_depth, dest_bit_depth, channels;
png_color palette[256];
png_byte trans_alpha[256];
png_color_16p trans_color;
int num_palette, num_trans, index;
unsigned int gray, red, green, blue, alpha;
unsigned int prev_gray, prev_red, prev_green, prev_blue, prev_alpha;
#ifdef PNG_bKGD_SUPPORTED
png_color_16p background;
#endif
png_uint_32 i, j;
opng_debug(1, "in opng_reduce_to_palette");
png_get_IHDR(png_ptr, info_ptr, &width, &height, &src_bit_depth,
&color_type, &interlace_type, &compression_type, &filter_type);
if (src_bit_depth != 8)
return OPNG_REDUCE_NONE; /* nothing is done in this case */
OPNG_ASSERT(!(color_type & PNG_COLOR_MASK_PALETTE));
row_ptr = png_get_rows(png_ptr, info_ptr);
channels = png_get_channels(png_ptr, info_ptr);
alpha_row = (png_bytep)png_malloc(png_ptr, width);
row_info.width = width;
row_info.rowbytes = 0; /* not used */
row_info.color_type = (png_byte)color_type;
row_info.bit_depth = (png_byte)src_bit_depth;
row_info.channels = (png_byte)channels;
row_info.pixel_depth = 0; /* not used */
/* Analyze the possibility of this reduction. */
num_palette = num_trans = 0;
trans_color = NULL;
png_get_tRNS(png_ptr, info_ptr, NULL, NULL, &trans_color);
prev_gray = prev_red = prev_green = prev_blue = prev_alpha = 256;
for (i = 0; i < height; ++i, ++row_ptr)
{
sample_ptr = *row_ptr;
opng_get_alpha_row(&row_info, trans_color, *row_ptr, alpha_row);
if (color_type & PNG_COLOR_MASK_COLOR)
{
for (j = 0; j < width; ++j, sample_ptr += channels)
{
red = sample_ptr[0];
green = sample_ptr[1];
blue = sample_ptr[2];
alpha = alpha_row[j];
/* Check the cache first. */
if (red != prev_red || green != prev_green || blue != prev_blue ||
alpha != prev_alpha)
{
prev_red = red;
prev_green = green;
prev_blue = blue;
prev_alpha = alpha;
if (opng_insert_palette_entry(palette, &num_palette,
trans_alpha, &num_trans, 256,
red, green, blue, alpha, &index) < 0) /* overflow */
{
OPNG_ASSERT(num_palette < 0);
i = height; /* forced exit from outer loop */
break;
}
}
}
}
else /* grayscale */
{
for (j = 0; j < width; ++j, sample_ptr += channels)
{
gray = sample_ptr[0];
alpha = alpha_row[j];
/* Check the cache first. */
if (gray != prev_gray || alpha != prev_alpha)
{
prev_gray = gray;
prev_alpha = alpha;
if (opng_insert_palette_entry(palette, &num_palette,
trans_alpha, &num_trans, 256,
gray, gray, gray, alpha, &index) < 0) /* overflow */
{
OPNG_ASSERT(num_palette < 0);
i = height; /* forced exit from outer loop */
break;
}
}
}
}
}
#ifdef PNG_bKGD_SUPPORTED
if ((num_palette >= 0) && png_get_bKGD(png_ptr, info_ptr, &background))
{
/* bKGD has an alpha-agnostic palette entry. */
if (color_type & PNG_COLOR_MASK_COLOR)
{
red = background->red;
green = background->green;
blue = background->blue;
}
else
red = green = blue = background->gray;
opng_insert_palette_entry(palette, &num_palette,
trans_alpha, &num_trans, 256,
red, green, blue, 256, &index);
if (index >= 0)
background->index = (png_byte)index;
}
#endif
/* Continue only if the uncompressed indexed image (pixels + PLTE + tRNS)
* is smaller than the uncompressed RGB(A) image.
* Casual overhead (headers, CRCs, etc.) is ignored.
*
* Compare:
* num_pixels * (src_bit_depth * channels - dest_bit_depth) / 8
* vs.
* sizeof(PLTE) + sizeof(tRNS)
*/
if (num_palette >= 0)
{
OPNG_ASSERT(num_palette > 0 && num_palette <= 256);
OPNG_ASSERT(num_trans >= 0 && num_trans <= num_palette);
if (num_palette <= 2)
dest_bit_depth = 1;
else if (num_palette <= 4)
dest_bit_depth = 2;
else if (num_palette <= 16)
dest_bit_depth = 4;
else
dest_bit_depth = 8;
/* Do the comparison in a way that does not cause overflow. */
if (channels * 8 == dest_bit_depth ||
(3 * num_palette + num_trans) * 8 / (channels * 8 - dest_bit_depth)
/ width / height >= 1)
num_palette = -1;
}
if (num_palette < 0) /* can't reduce */
{
png_free(png_ptr, alpha_row);
return OPNG_REDUCE_NONE;
}
/* Reduce. */
row_ptr = png_get_rows(png_ptr, info_ptr);
index = -1;
prev_red = prev_green = prev_blue = prev_alpha = (unsigned int)(-1);
for (i = 0; i < height; ++i, ++row_ptr)
{
sample_ptr = *row_ptr;
opng_get_alpha_row(&row_info, trans_color, *row_ptr, alpha_row);
if (color_type & PNG_COLOR_MASK_COLOR)
{
for (j = 0; j < width; ++j, sample_ptr += channels)
{
red = sample_ptr[0];
green = sample_ptr[1];
blue = sample_ptr[2];
alpha = alpha_row[j];
/* Check the cache first. */
if (red != prev_red || green != prev_green || blue != prev_blue ||
alpha != prev_alpha)
{
prev_red = red;
prev_green = green;
prev_blue = blue;
prev_alpha = alpha;
if (opng_insert_palette_entry(palette, &num_palette,
trans_alpha, &num_trans, 256,
red, green, blue, alpha, &index) != 0)
index = -1; /* this should not happen */
}
OPNG_ASSERT(index >= 0);
(*row_ptr)[j] = (png_byte)index;
}
}
else /* grayscale */
{
for (j = 0; j < width; ++j, sample_ptr += channels)
{
gray = sample_ptr[0];
alpha = alpha_row[j];
/* Check the cache first. */
if (gray != prev_gray || alpha != prev_alpha)
{
prev_gray = gray;
prev_alpha = alpha;
if (opng_insert_palette_entry(palette, &num_palette,
trans_alpha, &num_trans, 256,
gray, gray, gray, alpha, &index) != 0)
index = -1; /* this should not happen */
}
OPNG_ASSERT(index >= 0);
(*row_ptr)[j] = (png_byte)index;
}
}
}
/* Update the image information. */
png_set_IHDR(png_ptr, info_ptr, width, height, 8, PNG_COLOR_TYPE_PALETTE,
interlace_type, compression_type, filter_type);
png_set_PLTE(png_ptr, info_ptr, palette, num_palette);
if (num_trans > 0)
png_set_tRNS(png_ptr, info_ptr, trans_alpha, num_trans, NULL);
/* bKGD (if present) is automatically updated. */
png_free(png_ptr, alpha_row);
result = OPNG_REDUCE_RGB_TO_PALETTE;
if (reductions & OPNG_REDUCE_8_TO_4_2_1)
result |= opng_reduce_palette_bits(png_ptr, info_ptr, reductions);
return result;
}
/*
* Analyze the usage of samples.
* The output value usage_map[n] indicates whether the sample n
* is used. The usage_map[] array must have 256 entries.
* The function requires a valid bit depth between 1 and 8.
*/
static void /* PRIVATE */
opng_analyze_sample_usage(png_structp png_ptr, png_infop info_ptr,
png_bytep usage_map)
{
png_bytepp row_ptr;
png_bytep sample_ptr;
png_uint_32 width, height;
int bit_depth, init_shift, init_mask, shift, mask;
#ifdef PNG_bKGD_SUPPORTED
png_color_16p background;
#endif
png_uint_32 i, j;
opng_debug(1, "in opng_analyze_sample_usage");
height = png_get_image_height(png_ptr, info_ptr);
width = png_get_image_width(png_ptr, info_ptr);
bit_depth = png_get_bit_depth(png_ptr, info_ptr);
row_ptr = png_get_rows(png_ptr, info_ptr);
/* Initialize the output entries with 0. */
memset(usage_map, 0, 256);
/* Iterate through all sample values. */
if (bit_depth == 8)
{
for (i = 0; i < height; ++i, ++row_ptr)
{
for (j = 0, sample_ptr = *row_ptr; j < width; ++j, ++sample_ptr)
usage_map[*sample_ptr] = 1;
}
}
else
{
OPNG_ASSERT(bit_depth < 8);
init_shift = 8 - bit_depth;
init_mask = (1 << 8) - (1 << init_shift);
for (i = 0; i < height; ++i, ++row_ptr)
{
for (j = 0, sample_ptr = *row_ptr; j < width; ++sample_ptr)
{
mask = init_mask;
shift = init_shift;
do
{
usage_map[(*sample_ptr & mask) >> shift] = 1;
mask >>= bit_depth;
shift -= bit_depth;
++j;
} while (mask > 0 && j < width);
}
}
}
#ifdef PNG_bKGD_SUPPORTED
/* bKGD also counts as a used sample. */
if (png_get_bKGD(png_ptr, info_ptr, &background))
usage_map[background->index] = 1;
#endif
}
/*
* Set the number of PLTE entries to a new value.
* Setting info_ptr->num_palette to num_palette, avoiding the temporary buffer,
* should have been sufficient, but can't be done using the current libpng API.
*/
static void /* PRIVATE */
opng_set_num_palette(png_structp png_ptr, png_infop info_ptr, int num_palette)
{
png_color buffer[PNG_MAX_PALETTE_LENGTH];
png_colorp palette;
int src_num_palette;
opng_debug(1, "in opng_set_num_palette");
OPNG_ASSERT(num_palette > 0);
src_num_palette = 0;
png_get_PLTE(png_ptr, info_ptr, &palette, &src_num_palette);
if (num_palette == src_num_palette)
return;
memcpy(buffer, palette, num_palette * sizeof(png_color));
if (num_palette > src_num_palette)
memset(buffer + src_num_palette, 0,
(num_palette - src_num_palette) * sizeof(png_color));
png_set_PLTE(png_ptr, info_ptr, buffer, num_palette);
}
/*
* Set the number of tRNS entries to a new value.
* Setting info_ptr->num_trans to num_trans, avoiding the temporary buffer,
* should have been sufficient, but can't be done using the current libpng API.
*/
static void /* PRIVATE */
opng_set_num_trans(png_structp png_ptr, png_infop info_ptr, int num_trans)
{
png_byte buffer[PNG_MAX_PALETTE_LENGTH];
png_bytep trans_alpha;
int src_num_trans;
opng_debug(1, "in opng_set_num_trans");
OPNG_ASSERT(num_trans > 0); /* tRNS should be invalidated in this case */
src_num_trans = 0;
png_get_tRNS(png_ptr, info_ptr, &trans_alpha, &src_num_trans, NULL);
if (num_trans == src_num_trans)
return;
memcpy(buffer, trans_alpha, (size_t)num_trans);
if (num_trans > src_num_trans)
memset(buffer + src_num_trans, 0, num_trans - src_num_trans);
png_set_tRNS(png_ptr, info_ptr, buffer, num_trans, NULL);
}
/*
* Reduce the palette. (Only the fast method is implemented.)
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
static png_uint_32 /* PRIVATE */
opng_reduce_palette(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_uint_32 result;
png_colorp palette;
png_bytep trans_alpha;
png_bytepp row_ptr;
png_uint_32 width, height;
int bit_depth, color_type, interlace_type, compression_type, filter_type;
int src_num_palette, src_num_trans;
int last_color_index, last_trans_index;
png_byte crt_trans_value, last_trans_value;
png_byte is_used[256];
png_color_16 gray_trans;
int is_gray;
#ifdef PNG_bKGD_SUPPORTED
png_color_16p background;
#endif
#ifdef PNG_hIST_SUPPORTED
png_uint_16p hist;
#endif
#ifdef PNG_sBIT_SUPPORTED
png_color_8p sig_bits;
#endif
png_uint_32 i, j;
int k;
opng_debug(1, "in opng_reduce_palette");
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth,
&color_type, &interlace_type, &compression_type, &filter_type);
row_ptr = png_get_rows(png_ptr, info_ptr);
if (!png_get_PLTE(png_ptr, info_ptr, &palette, &src_num_palette))
{
palette = NULL;
src_num_palette = 0;
}
if (!png_get_tRNS(png_ptr, info_ptr, &trans_alpha, &src_num_trans, NULL))
{
trans_alpha = NULL;
src_num_trans = 0;
}
else
OPNG_ASSERT(trans_alpha != NULL && src_num_trans > 0);
opng_analyze_sample_usage(png_ptr, info_ptr, is_used);
/* Palette-to-gray does not work (yet) if the bit depth is below 8. */
is_gray = (reductions & OPNG_REDUCE_PALETTE_TO_GRAY) && (bit_depth == 8);
last_color_index = last_trans_index = -1;
for (k = 0; k < 256; ++k)
{
if (!is_used[k])
continue;
last_color_index = k;
if (k < src_num_trans && trans_alpha[k] < 255)
last_trans_index = k;
if (is_gray)
if (palette[k].red != palette[k].green ||
palette[k].red != palette[k].blue)
is_gray = 0;
}
OPNG_ASSERT(last_color_index >= 0);
OPNG_ASSERT(last_color_index >= last_trans_index);
/* Check the integrity of PLTE and tRNS. */
if (last_color_index >= src_num_palette)
{
png_warning(png_ptr, "Too few colors in palette");
/* Fix the palette by adding blank entries at the end. */
src_num_palette = last_color_index + 1;
opng_set_num_palette(png_ptr, info_ptr, src_num_palette);
}
if (src_num_trans > src_num_palette)
{
png_warning(png_ptr, "Too many alpha values in tRNS");
/* Transparency will be fixed further below. */
}
/* Check if tRNS can be reduced to grayscale. */
if (is_gray && last_trans_index >= 0)
{
gray_trans.gray = palette[last_trans_index].red;
last_trans_value = trans_alpha[last_trans_index];
for (k = 0; k <= last_color_index; ++k)
{
if (!is_used[k])
continue;
if (k <= last_trans_index)
{
crt_trans_value = trans_alpha[k];
/* Cannot reduce if different colors have transparency. */
if (crt_trans_value < 255 && palette[k].red != gray_trans.gray)
{
is_gray = 0;
break;
}
}
else
crt_trans_value = 255;
/* Cannot reduce if same color has multiple transparency levels. */
if (palette[k].red == gray_trans.gray &&
crt_trans_value != last_trans_value)
{
is_gray = 0;
break;
}
}
}
/* Initialize result value. */
result = OPNG_REDUCE_NONE;
/* Remove tRNS if it is entirely sterile. */
if (src_num_trans > 0 && last_trans_index < 0)
{
src_num_trans = 0;
png_free_data(png_ptr, info_ptr, PNG_FREE_TRNS, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_tRNS);
result = OPNG_REDUCE_PALETTE_FAST;
}
if (reductions & OPNG_REDUCE_PALETTE_FAST)
{
if (src_num_palette != last_color_index + 1)
{
/* Reduce PLTE. */
/* hIST is reduced automatically. */
opng_set_num_palette(png_ptr, info_ptr, last_color_index + 1);
result = OPNG_REDUCE_PALETTE_FAST;
}
if (src_num_trans > 0 && src_num_trans != last_trans_index + 1)
{
/* Reduce tRNS. */
opng_set_num_trans(png_ptr, info_ptr, last_trans_index + 1);
result = OPNG_REDUCE_PALETTE_FAST;
}
}
if (reductions & OPNG_REDUCE_8_TO_4_2_1)
{
result |= opng_reduce_palette_bits(png_ptr, info_ptr, reductions);
/* Refresh the image information. */
bit_depth = png_get_bit_depth(png_ptr, info_ptr);
}
if ((bit_depth < 8) || !is_gray)
return result;
/* Reduce palette --> grayscale. */
for (i = 0; i < height; ++i)
{
for (j = 0; j < width; ++j)
row_ptr[i][j] = palette[row_ptr[i][j]].red;
}
/* Update the ancillary information. */
if (src_num_trans > 0)
png_set_tRNS(png_ptr, info_ptr, NULL, 0, &gray_trans);
#ifdef PNG_bKGD_SUPPORTED
if (png_get_bKGD(png_ptr, info_ptr, &background))
background->gray = palette[background->index].red;
#endif
#ifdef PNG_hIST_SUPPORTED
if (png_get_hIST(png_ptr, info_ptr, &hist))
{
png_free_data(png_ptr, info_ptr, PNG_FREE_HIST, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_hIST);
}
#endif
#ifdef PNG_sBIT_SUPPORTED
if (png_get_sBIT(png_ptr, info_ptr, &sig_bits))
{
png_byte max_sig_bits = sig_bits->red;
if (max_sig_bits < sig_bits->green)
max_sig_bits = sig_bits->green;
if (max_sig_bits < sig_bits->blue)
max_sig_bits = sig_bits->blue;
sig_bits->gray = max_sig_bits;
}
#endif
/* Update the image information. */
png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
PNG_COLOR_TYPE_GRAY, interlace_type, compression_type, filter_type);
png_free_data(png_ptr, info_ptr, PNG_FREE_PLTE, -1);
png_set_invalid(png_ptr, info_ptr, PNG_INFO_PLTE);
return OPNG_REDUCE_PALETTE_TO_GRAY; /* ignore the former result */
}
/*
* Reduce the image (bit depth + color type + palette) without
* losing any information. The palette (if applicable) and the
* image data must be present (e.g. by calling png_set_rows(),
* or by loading IDAT).
* The parameter reductions indicates the intended reductions.
* The function returns the successful reductions.
*/
png_uint_32 PNGAPI
opng_reduce_image(png_structp png_ptr, png_infop info_ptr,
png_uint_32 reductions)
{
png_uint_32 result;
int color_type;
opng_debug(1, "in opng_reduce_image_type");
if (!opng_validate_image(png_ptr, info_ptr))
{
png_warning(png_ptr,
"Image reduction requires the presence of all critical information");
return OPNG_REDUCE_NONE;
}
color_type = png_get_color_type(png_ptr, info_ptr);
/* The reductions below must be applied in this particular order. */
/* Try to reduce the high bits and color/alpha channels. */
result = opng_reduce_bits(png_ptr, info_ptr, reductions);
/* Try to reduce the palette image. */
if (color_type == PNG_COLOR_TYPE_PALETTE &&
(reductions &
(OPNG_REDUCE_PALETTE_TO_GRAY |
OPNG_REDUCE_PALETTE_FAST |
OPNG_REDUCE_8_TO_4_2_1)))
result |= opng_reduce_palette(png_ptr, info_ptr, reductions);
/* Try to reduce RGB to palette or grayscale to palette. */
if (((color_type & ~PNG_COLOR_MASK_ALPHA) == PNG_COLOR_TYPE_GRAY &&
(reductions & OPNG_REDUCE_GRAY_TO_PALETTE)) ||
((color_type & ~PNG_COLOR_MASK_ALPHA) == PNG_COLOR_TYPE_RGB &&
(reductions & OPNG_REDUCE_RGB_TO_PALETTE)))
{
if (!(result & OPNG_REDUCE_PALETTE_TO_GRAY))
result |= opng_reduce_to_palette(png_ptr, info_ptr, reductions);
}
return result;
}
#endif /* OPNG_IMAGE_REDUCTIONS_SUPPORTED */