libpng的简单使用

这个用了好多次了，在blog上记录一下吧

 

int SavePng(const string &png_file_name, byte **data, int width, int height, int bit_depth, png_colorp palette, int palette_len){png_structp png_ptr;png_infop info_ptr;FILE *png_file = fopen(png_file_name.c_str(), "wb");assert(png_file);png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);if(png_ptr == NULL){cerr<<"ERROR:png_create_write_struct/n";return 0;}info_ptr = png_create_info_struct(png_ptr);if(info_ptr == NULL){cerr<<"ERROR:png_create_info_struct/n";png_destroy_write_struct(&png_ptr, NULL);return 0;}png_init_io(png_ptr, png_file);png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_PALETTE,PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);png_set_PLTE(png_ptr, info_ptr, palette, palette_len);png_write_info(png_ptr, info_ptr); //这里就是图像数据了png_bytepp row_pointers = new png_bytep[height];for (int i=0; i<height; ++i){row_pointers[i] = (png_bytep)data[i];}png_write_image(png_ptr, row_pointers);delete row_pointers;png_write_end(png_ptr, info_ptr);png_free(png_ptr, palette);palette=NULL;png_destroy_write_struct(&png_ptr, &info_ptr);fclose(png_file);return 0;}void ReadPng(const string &png_file, byte *buf, byte real_bit_dep){FILE *file = fopen(png_file.c_str(), "rb");assert(file);// create read structpng_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);assert(png_ptr);// create info structpng_infop info_ptr = png_create_info_struct(png_ptr);assert(info_ptr);// I/O initialization using standard C streamspng_init_io(png_ptr, file);// read entire image , ignore alpha channelpng_read_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY|PNG_TRANSFORM_STRIP_ALPHA, NULL);int width = info_ptr->width;int height = info_ptr->height;int color_type = info_ptr->color_type;int bit_dep = info_ptr->pixel_depth; //这里要注意任何小于8bpp的图像被ps打开后都会被默认保存成8bpp的格式if (bit_dep < 8){png_destroy_read_struct(&png_ptr, &info_ptr, 0);fclose(file);return;}uint line_bytes = (uint)(width*bit_dep/8.0);printf("%d %d %d line_bytes=%d/n", width, height, bit_dep, line_bytes);//read pic datapng_bytep* row_pointers = png_get_rows(png_ptr,info_ptr);uint real_line_bytes = (uint)(width*real_bit_dep/8.0);byte* real_ptr = new byte[real_line_bytes];//write data to bufuint buf_offset = 0;printf("real_bit_dep = %d/n", real_bit_dep);for (int i=0; i<height; ++i){ //2bpp的情况if (real_bit_dep == 2){for (uint j=0, t=0; j<real_line_bytes; ++j, t+=4){real_ptr[j] = ((row_pointers[i][t+3]&0x3)<<6) | ((row_pointers[i][t+2]&0x3)<<4) | ((row_pointers[i][t+1]&0x3)<<2) | (row_pointers[i][t]&0x3);}} //4bpp的情况else if (real_bit_dep == 4){for (uint j=0, t=0; j<real_line_bytes; ++j, t+=2)real_ptr[j] = ((row_pointers[i][t+1]&0xF) << 4) | (row_pointers[i][t]&0xF);}memcpy(&buf[buf_offset], real_ptr, real_line_bytes);buf_offset += real_line_bytes;}// free memorypng_destroy_read_struct(&png_ptr, &info_ptr, 0);// close filefclose(file);}