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1311 lines
41 KiB
C
1311 lines
41 KiB
C
/*
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* opngreduc.c - libpng extension: lossless image reductions.
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*
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* Copyright (C) 2003-2011 Cosmin Truta.
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* This software is distributed under the same licensing and warranty terms
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* as libpng.
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*/
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/* CAUTION:
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* Image reductions do not work well under certain transformations.
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*
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* Transformations like PNG_BGR, PNG_SWAP_BYTES, PNG_FILLER, PNG_INVERT_ALPHA,
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* and possibly others, require special treatment. However, the libpng API
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* does not currently convey the effect of transformations on its internal
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* state or on the layout of pixel data.
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*
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* Transformations which affect pixel depth (e.g. PNG_FILLER) are especially
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* dangerous when used in conjunction with this code, and should be avoided.
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*/
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#include "opngreduc.h"
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#ifndef OPNG_ASSERT
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#include <assert.h>
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#define OPNG_ASSERT(cond) assert(cond)
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#define OPNG_ASSERT_MSG(cond, msg) assert(cond)
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#endif
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#ifdef png_debug
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#define opng_debug(level, msg) png_debug(level, msg)
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#else
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#define opng_debug(level, msg) ((void)0)
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#endif
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#ifdef PNG_INFO_IMAGE_SUPPORTED
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/*
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* Check if the image information is valid.
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* The image information is said to be valid if all the required
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* critical chunk data is present in the png structures.
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* The function returns 1 if this information is valid, and 0 otherwise.
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*/
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int PNGAPI
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opng_validate_image(png_structp png_ptr, png_infop info_ptr)
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{
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opng_debug(1, "in opng_validate_image");
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/* Validate IHDR. */
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if (png_get_bit_depth(png_ptr, info_ptr) == 0)
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return 0;
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/* Validate PLTE. */
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if (png_get_color_type(png_ptr, info_ptr) & PNG_COLOR_MASK_PALETTE)
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{
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if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_PLTE))
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return 0;
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}
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/* Validate IDAT. */
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if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_IDAT))
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return 0;
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return 1;
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}
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#endif /* PNG_INFO_IMAGE_SUPPORTED */
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#ifdef OPNG_IMAGE_REDUCTIONS_SUPPORTED
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#define OPNG_CMP_RGB(R1, G1, B1, R2, G2, B2) \
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(((int)(R1) != (int)(R2)) ? \
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((int)(R1) - (int)(R2)) : \
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(((int)(G1) != (int)(G2)) ? \
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((int)(G1) - (int)(G2)) : \
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((int)(B1) - (int)(B2))))
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#define OPNG_CMP_ARGB(A1, R1, G1, B1, A2, R2, G2, B2) \
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(((int)(A1) != (int)(A2)) ? \
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((int)(A1) - (int)(A2)) : \
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(((int)(R1) != (R2)) ? \
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((int)(R1) - (int)(R2)) : \
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(((int)(G1) != (int)(G2)) ? \
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((int)(G1) - (int)(G2)) : \
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((int)(B1) - (int)(B2)))))
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/*
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* Build a color+alpha palette in which the entries are sorted by
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* (alpha, red, green, blue), in this particular order.
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* Use the insertion sort algorithm.
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* The alpha value is ignored if it is not in the range [0 .. 255].
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* The function returns:
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* 1 if the insertion is successful; *index = position of new entry.
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* 0 if the insertion is unnecessary; *index = position of crt entry.
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* -1 if overflow; *num_palette = *num_trans = *index = -1.
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*/
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static int /* PRIVATE */
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opng_insert_palette_entry(png_colorp palette, int *num_palette,
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png_bytep trans_alpha, int *num_trans, int max_tuples,
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unsigned int red, unsigned int green, unsigned int blue, unsigned int alpha,
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int *index)
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{
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int low, high, mid, cmp;
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int i;
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OPNG_ASSERT(*num_palette >= 0 && *num_palette <= max_tuples);
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OPNG_ASSERT(*num_trans >= 0 && *num_trans <= *num_palette);
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if (alpha < 255)
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{
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/* Do a binary search among transparent tuples. */
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low = 0;
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high = *num_trans - 1;
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while (low <= high)
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{
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mid = (low + high) / 2;
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cmp = OPNG_CMP_ARGB(alpha, red, green, blue,
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trans_alpha[mid],
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palette[mid].red, palette[mid].green, palette[mid].blue);
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if (cmp < 0)
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high = mid - 1;
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else if (cmp > 0)
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low = mid + 1;
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else
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{
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*index = mid;
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return 0;
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}
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}
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}
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else /* alpha == 255 || alpha not in [0 .. 255] */
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{
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/* Do a (faster) binary search among opaque tuples. */
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low = *num_trans;
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high = *num_palette - 1;
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while (low <= high)
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{
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mid = (low + high) / 2;
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cmp = OPNG_CMP_RGB(red, green, blue,
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palette[mid].red, palette[mid].green, palette[mid].blue);
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if (cmp < 0)
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high = mid - 1;
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else if (cmp > 0)
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low = mid + 1;
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else
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{
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*index = mid;
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return 0;
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}
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}
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}
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if (alpha > 255)
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{
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/* The binary search among opaque tuples has failed. */
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/* Do a linear search among transparent tuples, ignoring alpha. */
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for (i = 0; i < *num_trans; ++i)
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{
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cmp = OPNG_CMP_RGB(red, green, blue,
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palette[i].red, palette[i].green, palette[i].blue);
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if (cmp == 0)
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{
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*index = i;
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return 0;
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}
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}
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}
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/* Check for overflow. */
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if (*num_palette >= max_tuples)
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{
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*num_palette = *num_trans = *index = -1;
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return -1;
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}
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/* Insert new tuple at [low]. */
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OPNG_ASSERT(low >= 0 && low <= *num_palette);
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for (i = *num_palette; i > low; --i)
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palette[i] = palette[i - 1];
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palette[low].red = (png_byte)red;
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palette[low].green = (png_byte)green;
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palette[low].blue = (png_byte)blue;
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++(*num_palette);
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if (alpha < 255)
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{
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OPNG_ASSERT(low <= *num_trans);
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for (i = *num_trans; i > low; --i)
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trans_alpha[i] = trans_alpha[i - 1];
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trans_alpha[low] = (png_byte)alpha;
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++(*num_trans);
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}
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*index = low;
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return 1;
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}
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/*
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* Retrieve the alpha samples from the given image row.
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*/
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static void /* PRIVATE */
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opng_get_alpha_row(png_row_infop row_info_ptr, png_color_16p trans_color,
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png_bytep row, png_bytep alpha_row)
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{
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png_bytep sample_ptr;
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png_uint_32 width;
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int color_type, bit_depth, channels;
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png_byte trans_red, trans_green, trans_blue, trans_gray;
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png_uint_32 i;
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width = row_info_ptr->width;
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color_type = row_info_ptr->color_type;
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bit_depth = row_info_ptr->bit_depth;
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channels = row_info_ptr->channels;
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OPNG_ASSERT(!(color_type & PNG_COLOR_MASK_PALETTE));
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OPNG_ASSERT(bit_depth == 8);
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if (!(color_type & PNG_COLOR_MASK_ALPHA))
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{
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if (trans_color == NULL)
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{
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/* All pixels are fully opaque. */
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memset(alpha_row, 255, (size_t)width);
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return;
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}
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if (color_type == PNG_COLOR_TYPE_RGB)
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{
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OPNG_ASSERT(channels == 3);
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trans_red = (png_byte)trans_color->red;
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trans_green = (png_byte)trans_color->green;
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trans_blue = (png_byte)trans_color->blue;
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sample_ptr = row;
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for (i = 0; i < width; ++i, sample_ptr += 3)
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alpha_row[i] = (png_byte)
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((sample_ptr[0] == trans_red &&
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sample_ptr[1] == trans_green &&
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sample_ptr[2] == trans_blue) ? 0 : 255);
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}
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else
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{
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OPNG_ASSERT(color_type == PNG_COLOR_TYPE_GRAY);
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OPNG_ASSERT(channels == 1);
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trans_gray = (png_byte)trans_color->gray;
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for (i = 0; i < width; ++i)
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alpha_row[i] = (png_byte)((row[i] == trans_gray) ? 0 : 255);
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}
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return;
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}
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/* There is a real alpha channel. The alpha sample is last in RGBA tuple. */
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OPNG_ASSERT(channels > 1);
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sample_ptr = row + (channels - 1);
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for (i = 0; i < width; ++i, sample_ptr += channels, ++alpha_row)
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*alpha_row = *sample_ptr;
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}
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/*
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* Analyze the redundancy of bits inside the image.
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* The parameter reductions indicates the intended reductions.
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* The function returns the possible reductions.
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*/
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static png_uint_32 /* PRIVATE */
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opng_analyze_bits(png_structp png_ptr, png_infop info_ptr,
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png_uint_32 reductions)
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{
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png_bytepp row_ptr;
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png_bytep component_ptr;
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png_uint_32 height, width;
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int bit_depth, color_type, byte_depth, channels, sample_size, offset_alpha;
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#ifdef PNG_bKGD_SUPPORTED
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png_color_16p background;
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#endif
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png_uint_32 i, j;
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opng_debug(1, "in opng_analyze_bits");
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png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
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NULL, NULL, NULL);
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if (bit_depth < 8)
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return OPNG_REDUCE_NONE; /* not applicable */
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if (color_type & PNG_COLOR_MASK_PALETTE)
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return OPNG_REDUCE_NONE; /* let opng_reduce_palette() handle it */
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byte_depth = bit_depth / 8;
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channels = png_get_channels(png_ptr, info_ptr);
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sample_size = channels * byte_depth;
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offset_alpha = (channels - 1) * byte_depth;
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/* Select the applicable reductions. */
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reductions &= (OPNG_REDUCE_16_TO_8 |
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OPNG_REDUCE_RGB_TO_GRAY | OPNG_REDUCE_STRIP_ALPHA);
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if (bit_depth <= 8)
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reductions &= ~OPNG_REDUCE_16_TO_8;
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if (!(color_type & PNG_COLOR_MASK_COLOR))
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reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
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if (!(color_type & PNG_COLOR_MASK_ALPHA))
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reductions &= ~OPNG_REDUCE_STRIP_ALPHA;
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/* Check if the ancillary information allows these reductions. */
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#ifdef PNG_bKGD_SUPPORTED
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if (png_get_bKGD(png_ptr, info_ptr, &background))
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{
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if (reductions & OPNG_REDUCE_16_TO_8)
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{
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if (background->red % 257 != 0 ||
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background->green % 257 != 0 ||
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background->blue % 257 != 0 ||
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background->gray % 257 != 0)
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reductions &= ~OPNG_REDUCE_16_TO_8;
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}
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if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
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{
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if (background->red != background->green ||
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background->red != background->blue)
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reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
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}
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}
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#endif
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/* Check for each possible reduction, row by row. */
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row_ptr = png_get_rows(png_ptr, info_ptr);
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for (i = 0; i < height; ++i, ++row_ptr)
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{
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if (reductions == OPNG_REDUCE_NONE)
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return OPNG_REDUCE_NONE; /* no need to go any further */
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/* Check if it is possible to reduce the bit depth to 8. */
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if (reductions & OPNG_REDUCE_16_TO_8)
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{
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component_ptr = *row_ptr;
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for (j = 0; j < channels * width; ++j, component_ptr += 2)
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{
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if (component_ptr[0] != component_ptr[1])
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{
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reductions &= ~OPNG_REDUCE_16_TO_8;
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break;
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}
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}
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}
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if (bit_depth == 8)
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{
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/* Check if it is possible to reduce rgb --> gray. */
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if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
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{
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component_ptr = *row_ptr;
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for (j = 0; j < width; ++j, component_ptr += sample_size)
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{
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if (component_ptr[0] != component_ptr[1] ||
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component_ptr[0] != component_ptr[2])
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{
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reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
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break;
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}
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}
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}
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/* Check if it is possible to strip the alpha channel. */
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if (reductions & OPNG_REDUCE_STRIP_ALPHA)
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{
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component_ptr = *row_ptr + offset_alpha;
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for (j = 0; j < width; ++j, component_ptr += sample_size)
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{
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if (component_ptr[0] != 255)
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{
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reductions &= ~OPNG_REDUCE_STRIP_ALPHA;
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break;
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}
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}
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}
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}
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else /* bit_depth == 16 */
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{
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/* Check if it is possible to reduce rgb --> gray. */
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if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
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{
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component_ptr = *row_ptr;
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for (j = 0; j < width; ++j, component_ptr += sample_size)
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{
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if (component_ptr[0] != component_ptr[2] ||
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component_ptr[0] != component_ptr[4] ||
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component_ptr[1] != component_ptr[3] ||
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component_ptr[1] != component_ptr[5])
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{
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reductions &= ~OPNG_REDUCE_RGB_TO_GRAY;
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break;
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}
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}
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}
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/* Check if it is possible to strip the alpha channel. */
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if (reductions & OPNG_REDUCE_STRIP_ALPHA)
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{
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component_ptr = *row_ptr + offset_alpha;
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for (j = 0; j < width; ++j, component_ptr += sample_size)
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{
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if (component_ptr[0] != 255 || component_ptr[1] != 255)
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{
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reductions &= ~OPNG_REDUCE_STRIP_ALPHA;
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break;
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}
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}
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}
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}
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}
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return reductions;
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}
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/*
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* Reduce the image type to a lower bit depth and color type,
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* by removing redundant bits.
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* Possible reductions: 16bpp to 8bpp; RGB to gray; strip alpha.
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* The parameter reductions indicates the intended reductions.
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* The function returns the successful reductions.
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* All reductions are performed in a single step.
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*/
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static png_uint_32 /* PRIVATE */
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opng_reduce_bits(png_structp png_ptr, png_infop info_ptr,
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png_uint_32 reductions)
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{
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png_bytepp row_ptr;
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png_bytep src_ptr, dest_ptr;
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png_uint_32 width, height;
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int interlace_type, compression_type, filter_type;
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int src_bit_depth, dest_bit_depth;
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int src_byte_depth, dest_byte_depth;
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int src_color_type, dest_color_type;
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int src_channels, dest_channels;
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int src_sample_size, dest_sample_size;
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int tran_tbl[8];
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png_color_16p trans_color;
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#ifdef PNG_bKGD_SUPPORTED
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png_color_16p background;
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#endif
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#ifdef PNG_sBIT_SUPPORTED
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png_color_8p sig_bits;
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#endif
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png_uint_32 i, j;
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int k;
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opng_debug(1, "in opng_reduce_bits");
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/* See which reductions may be performed. */
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reductions = opng_analyze_bits(png_ptr, info_ptr, reductions);
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if (reductions == OPNG_REDUCE_NONE)
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return OPNG_REDUCE_NONE; /* exit early */
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png_get_IHDR(png_ptr, info_ptr, &width, &height,
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&src_bit_depth, &src_color_type,
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&interlace_type, &compression_type, &filter_type);
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/* Compute the new image parameters bit_depth, color_type, etc. */
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OPNG_ASSERT(src_bit_depth >= 8);
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if (reductions & OPNG_REDUCE_16_TO_8)
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{
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OPNG_ASSERT(src_bit_depth == 16);
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dest_bit_depth = 8;
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}
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else
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dest_bit_depth = src_bit_depth;
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src_byte_depth = src_bit_depth / 8;
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dest_byte_depth = dest_bit_depth / 8;
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dest_color_type = src_color_type;
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if (reductions & OPNG_REDUCE_RGB_TO_GRAY)
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{
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OPNG_ASSERT(src_color_type & PNG_COLOR_MASK_COLOR);
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dest_color_type &= ~PNG_COLOR_MASK_COLOR;
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}
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if (reductions & OPNG_REDUCE_STRIP_ALPHA)
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{
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OPNG_ASSERT(src_color_type & PNG_COLOR_MASK_ALPHA);
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dest_color_type &= ~PNG_COLOR_MASK_ALPHA;
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}
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src_channels = png_get_channels(png_ptr, info_ptr);
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dest_channels =
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((dest_color_type & PNG_COLOR_MASK_COLOR) ? 3 : 1) +
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((dest_color_type & PNG_COLOR_MASK_ALPHA) ? 1 : 0);
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src_sample_size = src_channels * src_byte_depth;
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dest_sample_size = dest_channels * dest_byte_depth;
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/* Pre-compute the intra-sample translation table. */
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for (k = 0; k < 4 * dest_byte_depth; ++k)
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tran_tbl[k] = k * src_bit_depth / dest_bit_depth;
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/* 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 */
|