libpng 库的源码包中有个 example.c ,里面包含PNG文件读/写的示例代码,参考示例代码和注释(虽然是英文的),可以了解大致的用法。
以下是读取PNG图片的图像数据的代码,使用前还需要按自己的需求补充剩余代码。
- #include <png.h>
- #define PNG_BYTES_TO_CHECK 4
-
- int load_png_image( const char *filepath,
- {
- FILE *fp;
- png_structp png_ptr;
- png_infop info_ptr;
- png_bytep* row_pointers;
- char buf[PNG_BYTES_TO_CHECK];
- int w, h, x, y, temp, color_type;
-
- fp = fopen( filepath, "rb" );
- if( fp == NULL ) {
- return
- }
-
- png_ptr = png_create_read_struct( PNG_LIBPNG_VER_STRING, 0, 0, 0 );
- info_ptr = png_create_info_struct( png_ptr );
-
- setjmp( png_jmpbuf(png_ptr) );
-
- temp = fread( buf, 1, PNG_BYTES_TO_CHECK, fp );
-
- if( temp < PNG_BYTES_TO_CHECK ) {
- fclose(fp);
- png_destroy_read_struct( &png_ptr, &info_ptr, 0);
- return
- }
-
- temp = png_sig_cmp( (png_bytep)buf, (png_size_t)0, PNG_BYTES_TO_CHECK );
-
- if( temp != 0 ) {
- fclose(fp);
- png_destroy_read_struct( &png_ptr, &info_ptr, 0);
- return
- }
-
-
- rewind( fp );
-
- png_init_io( png_ptr, fp );
-
- png_read_png( png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0 );
-
- color_type = png_get_color_type( png_ptr, info_ptr );
-
- w = png_get_image_width( png_ptr, info_ptr );
- h = png_get_image_height( png_ptr, info_ptr );
-
- row_pointers = png_get_rows( png_ptr, info_ptr );
-
- switch( color_type ) {
- case PNG_COLOR_TYPE_RGB_ALPHA:
- for( y=0; y<h; ++y ) {
- for( x=0; x<w*4; ) {
-
-
-
-
-
- }
- }
- break;
-
- case PNG_COLOR_TYPE_RGB:
- for( y=0; y<h; ++y ) {
- for( x=0; x<w*3; ) {
-
-
-
- }
- }
- break;
-
- default:
- fclose(fp);
- png_destroy_read_struct( &png_ptr, &info_ptr, 0);
- return
- }
- png_destroy_read_struct( &png_ptr, &info_ptr, 0);
- return 0;
- }
以下是生成png图片文件的代码,也就是照搬了 example.c 里的 write_png() 的代码,稍微翻译了主要的注释。
- void write_png(char *file_name
- {
- FILE *fp;
- png_structp png_ptr;
- png_infop info_ptr;
- png_colorp palette;
-
-
- fp = fopen(file_name, "wb");
- if (fp == NULL)
- return (ERROR);
-
-
- png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
- png_voidp user_error_ptr, user_error_fn, user_warning_fn);
-
- if (png_ptr == NULL)
- {
- fclose(fp);
- return (ERROR);
- }
-
-
- info_ptr = png_create_info_struct(png_ptr);
- if (info_ptr == NULL)
- {
- fclose(fp);
- png_destroy_write_struct(&png_ptr, NULL);
- return (ERROR);
- }
-
-
- if (setjmp(png_jmpbuf(png_ptr)))
- {
-
- fclose(fp);
- png_destroy_write_struct(&png_ptr, &info_ptr);
- return (ERROR);
- }
-
-
-
- #ifdef streams /* I/O 初始化方法 1 */
-
- png_init_io(png_ptr, fp);
-
- #else no_streams /* I/O 初始化方法 2 */
-
- png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
- user_IO_flush_function);
-
- #endif no_streams /* 只能选择一种初始化方式 */
-
- #ifdef hilevel
-
- png_write_png(png_ptr, info_ptr, png_transforms, NULL);
-
- #else
-
-
-
- png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
- PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
-
-
- palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH
- * (sizeof (png_color)));
-
- png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
-
-
-
- png_color_8 sig_bit;
-
-
- sig_bit.gray = true_bit_depth;
-
-
- sig_bit.red = true_red_bit_depth;
- sig_bit.green = true_green_bit_depth;
- sig_bit.blue = true_blue_bit_depth;
-
-
- sig_bit.alpha = true_alpha_bit_depth;
-
- png_set_sBIT(png_ptr, info_ptr, &sig_bit);
-
-
-
- png_set_gAMA(png_ptr, info_ptr, gamma);
-
-
- {
- png_text text_ptr[3];
-
- char key0[]="Title";
- char text0[]="Mona Lisa";
- text_ptr[0].key = key0;
- text_ptr[0].text = text0;
- text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
- text_ptr[0].itxt_length = 0;
- text_ptr[0].lang = NULL;
- text_ptr[0].lang_key = NULL;
-
- char key1[]="Author";
- char text1[]="Leonardo DaVinci";
- text_ptr[1].key = key1;
- text_ptr[1].text = text1;
- text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
- text_ptr[1].itxt_length = 0;
- text_ptr[1].lang = NULL;
- text_ptr[1].lang_key = NULL;
-
- char key2[]="Description";
- char text2[]="<long text>";
- text_ptr[2].key = key2;
- text_ptr[2].text = text2;
- text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
- text_ptr[2].itxt_length = 0;
- text_ptr[2].lang = NULL;
- text_ptr[2].lang_key = NULL;
-
- png_set_text(write_ptr, write_info_ptr, text_ptr, 3);
- }
-
-
-
-
-
-
- png_write_info(png_ptr, info_ptr);
-
-
-
-
-
-
-
-
- png_set_invert_mono(png_ptr);
-
-
- png_set_shift(png_ptr, &sig_bit);
-
-
- png_set_packing(png_ptr);
-
-
- png_set_swap_alpha(png_ptr);
-
-
- png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
-
-
- png_set_bgr(png_ptr);
-
-
- png_set_swap(png_ptr);
-
-
- png_set_packswap(png_ptr);
-
-
- if (interlacing != 0)
- number_passes = png_set_interlace_handling(png_ptr);
-
- else
- number_passes = 1;
-
-
- png_uint_32 k, height, width;
-
-
- png_byte image[height*width*bytes_per_pixel];
-
- png_bytep row_pointers[height];
-
- if (height > PNG_UINT_32_MAX/(sizeof (png_bytep)))
- png_error (png_ptr, "Image is too tall to process in memory");
-
-
- for (k = 0; k < height; k++)
- row_pointers[k] = image + k*width*bytes_per_pixel;
-
-
-
- #ifdef entire /* 一次调用就将整个图像写进文件 */
- png_write_image(png_ptr, row_pointers);
-
-
-
- #else no_entire /* 用一个或多个扫描线写出图像数据 */
-
-
- for (pass = 0; pass < number_passes; pass++)
- {
-
- png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
-
-
- for (y = 0; y < height; y++)
- png_write_rows(png_ptr, &row_pointers[y], 1);
- }
- #endif no_entire /*只能选择一种输出方式 */
-
-
-
-
- png_write_end(png_ptr, info_ptr);
- #endif hilevel
-
-
- png_free(png_ptr, palette);
- palette = NULL;
-
-
- png_free(png_ptr, trans);
- trans = NULL;
-
-
-
- png_destroy_write_struct(&png_ptr, &info_ptr);
-
-
- fclose(fp);
-
-
- return (OK);
- }
删掉那些可选的代码,write_png() 的主要代码也就这些:
- void write_png(char *file_name
- {
- FILE *fp;
- png_structp png_ptr;
- png_infop info_ptr;
- png_colorp palette;
-
-
- fp = fopen(file_name, "wb");
- if (fp == NULL)
- return (ERROR);
-
-
- png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
-
- if (png_ptr == NULL)
- {
- fclose(fp);
- return (ERROR);
- }
-
-
- info_ptr = png_create_info_struct(png_ptr);
- if (info_ptr == NULL)
- {
- fclose(fp);
- png_destroy_write_struct(&png_ptr, NULL);
- return (ERROR);
- }
-
-
- if (setjmp(png_jmpbuf(png_ptr)))
- {
-
- fclose(fp);
- png_destroy_write_struct(&png_ptr, &info_ptr);
- return (ERROR);
- }
-
-
- png_init_io(png_ptr, fp);
-
-
-
-
- png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
- PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
-
-
- png_write_info(png_ptr, info_ptr);
-
- png_uint_32 k, height, width;
-
-
- png_byte image[height*width*bytes_per_pixel];
-
- png_bytep row_pointers[height];
-
- if (height > PNG_UINT_32_MAX/(sizeof (png_bytep)))
- png_error (png_ptr, "Image is too tall to process in memory");
-
-
- for (k = 0; k < height; k++)
- row_pointers[k] = image + k*width*bytes_per_pixel;
-
-
- png_write_image(png_ptr, row_pointers);
-
- png_write_end(png_ptr, info_ptr);
-
- png_destroy_write_struct(&png_ptr, &info_ptr);
-
- fclose(fp);
-
-
- return (OK);
- }
LIBPNG
原文:http://www.cnblogs.com/zhoug2020/p/6287552.html