/* * 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 #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 */