【数字图像处理】编码解码jpeg和png图片（C语言实现）

2024-01-10 15:12| 来源: 网络整理| 查看: 265

摘要：在本篇文章中本人将简单阐述图片编码的原理与实现方法。同时通过 windows平台下 mingw编译的libjpeg，libpng, zlib 第三方库，然后实现两种图片的编码与解码。

（一）写在前面

前一段时间本人一直在进行Opencv有关的学习，可是在学完了一堆又一堆的函数之后，发现自己对于图像处理的知识其实本质上还是什么都不会。我相信真正图像处理一定不是仅仅调用几个函数就可以了事的，一些东西如果不自己敲一遍恐怕永远也无法懂得其真正的原理。所以我打算从最底层自己敲出一个轻量级的图像处理库出来。可能一开始我的代码并不可靠效率可能也赶不上那些开源库的效率，但是我坚信这个轮子造的一定是有意义的。截止目前为之，这个图像处理的库已经可以支持jpeg,png,bmp三种图片格式的编码和解码。同时对于一些图片的常见几何变化，灰度变换，颜色识别等功能都已经分别进行了实现。而且截止目前仍然具有跨平台的特性。稍作修改便可以运行在 X86_LINUX,ARN_LINUX,STM32 等平台上面。下面的计划就是进一步的扩展界面显示的功能。比较凄惨的是找了半天也没有找到合适又简单的C语言跨平台图像库，这个再自己写又好像不太现实，所以决定开始导入QT作为图像显示的载体。

我目前已经将这个项目开源于github LiteCV

（二）基础知识（1）图像的压缩与解码

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（2）常用的图像压缩方法

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1.哈夫曼编码

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2.香农范诺编码

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（2）静止图像压缩编码标准（JPEG）

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看了那么多PPT个人感觉还是没有完全搞明白JPEG是个什么东西，感觉主要就是往频域做了一步变化，然后就是一顿骚操作，看起开似乎要自己写是不可能了，确实有些复杂。那就只能调用库文件了，好在这几个库都是开源的跨平台的时候直接编译一下就好了。

关于库的编译我就不细说了，不像opencv编译的时候那么多坑，装一个cmake就可以轻松编译成功了。要是实在懒得去编译可以到我的gihub代码仓库里面找一下，是有那几个第三方库的源码和库文件的。

（三）软件实现 jpeg.c /* * @Descripttion: 向licvcore 提供jpegJ读写接口 * @version: V 2.0 * @Author: Yueyang * @email: [email protected] * @Date: 2020-11-10 22:18:19 * @LastEditors: Yueyang * @LastEditTime: 2020-11-10 22:40:47 */ #ifndef JPEG_C #define JPEG_C #ifdef USE_JPEG #include "jconfig.h" #include "jmorecfg.h" #include #include #include "cv.h" /** * @name: * @msg: 将RGB数据编码并写JPG图片 * @param * char *filepath 图片路径 * JSAMPLE *image_buffer RGB数据指针 * int quality 图片质量 * int image_width 图片高度 * int image_height 图片宽度 * @return 0 (right) or -1(something wrong) */ BYTE Write_Jpeg(BYTE *filepath,JSAMPLE *image_buffer, LONG quality,LONG image_width,LONG image_height) { struct jpeg_compress_struct cinfo; struct jpeg_error_mgr jerr; FILE *outfile; JSAMPROW row_pointer[1]; int row_stride; cinfo.err = jpeg_std_error(&jerr); /* Now we can initialize the JPEG compression object. */ jpeg_create_compress(&cinfo); if ((outfile = fopen(filepath, "wb")) == NULL) { LILOG("can't open"); return -1; } jpeg_stdio_dest(&cinfo, outfile); cinfo.image_width = image_width; cinfo.image_height = image_height; cinfo.input_components = 3; cinfo.in_color_space = JCS_RGB; jpeg_set_defaults(&cinfo); jpeg_set_quality(&cinfo, quality, TRUE); jpeg_start_compress(&cinfo, TRUE); row_stride = (image_width * 3 + 3) & ~3; int i=0,j=0; for(i=0;i row_pointer[0] = &image_buffer[(cinfo.image_height-cinfo.next_scanline) * row_stride]; (void)jpeg_write_scanlines(&cinfo, row_pointer, 1); } jpeg_finish_compress(&cinfo); fclose(outfile); jpeg_destroy_compress(&cinfo); } struct my_error_mgr { struct jpeg_error_mgr pub; jmp_buf setjmp_buffer; }; typedef struct my_error_mgr *my_error_ptr; METHODDEF(void) my_error_exit(j_common_ptr cinfo) { my_error_ptr myerr = (my_error_ptr)cinfo->err; (*cinfo->err->output_message) (cinfo); longjmp(myerr->setjmp_buffer, 1); } /** * @name: Read_Jpeg * @msg: 读取一个JPG图片 * @param char* filepath 图片路径 * LONG* wdith 返回图片的宽度 * LONG* height 返回图片的高度 * @return 数据指针 */ BYTE* Read_Jpeg(char* filepath,LONG* width,LONG* height) { BYTE *imgData; struct jpeg_decompress_struct cinfo; struct my_error_mgr jerr; FILE *infile; JSAMPARRAY buffer; int row_stride; if ((infile = fopen(filepath, "rb")) == NULL) { LILOG("can't open"); } cinfo.err = jpeg_std_error(&jerr.pub); jerr.pub.error_exit = my_error_exit; if (setjmp(jerr.setjmp_buffer)) { LILOG("ERROR"); jpeg_destroy_decompress(&cinfo); fclose(infile); } jpeg_create_decompress(&cinfo); jpeg_stdio_src(&cinfo, infile); jpeg_read_header(&cinfo, TRUE); jpeg_start_decompress(&cinfo); row_stride = (cinfo.output_width * 3 ); imgData=(BYTE*)malloc(cinfo.output_height*cinfo.output_width*3); buffer =malloc(row_stride*1); while (cinfo.output_scanline *(imgData+(cinfo.output_height-cinfo.output_scanline)*row_stride+3*x+2) = *p++; *(imgData+(cinfo.output_height-cinfo.output_scanline)*row_stride+3*x+1) = *p++; *(imgData+(cinfo.output_height-cinfo.output_scanline)*row_stride+3*x+0) = *p++; } } *width=cinfo.output_width; *height=cinfo.output_height; free(buffer); (void)jpeg_finish_decompress(&cinfo); jpeg_destroy_decompress(&cinfo); fclose(infile); return imgData; } #endif //USE_JPEG #endif // !JPE_CG png.c /* * @Descripttion: 向licvcore 提供png读写接口 * @version: V 2.0 * @Author: Yueyang * @email: [email protected] * @Date: 2020-11-10 22:18:19 * @LastEditors: Yueyang * @LastEditTime: 2020-11-10 22:41:48 */ #ifndef LI_PNG_C #define LI_PNG_C #ifdef USE_PNG #include "png.h" #include "cv.h" #define PNG_BYTES_TO_CHECK 8 #define HAVE_ALPHA 1 #define NOT_HAVE_ALPHA 0 typedef struct _pic_data pic_data; struct _pic_data { int width, height; //长宽 int bit_depth; //位深度 int alpha_flag; //是否有透明通道 unsigned char *rgba;//实际rgb数据 }; BYTE check_is_png(FILE **fp, const char *filename) //检查是否png文件 { char checkheader[PNG_BYTES_TO_CHECK]; //查询是否png头 *fp = fopen(filename, "rb"); if (*fp == NULL) { LILOG("open failed ...1\n"); return -1; } if (fread(checkheader, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK) //读取png文件长度错误直接退出 return 0; return png_sig_cmp(checkheader, 0, PNG_BYTES_TO_CHECK); //0正确, 非0错误 } /** * @name: Read_Png * @msg: 读取一个png图片 * @param char* filepath 图片路径 * LONG* wdith 返回图片的宽度 * LONG* height 返回图片的高度 * BYTE* withalpha 是否带有alpha通道 * @return 数据指针注：一定返回一个24位的数据指针 */ BYTE* Read_Png(BYTE *filename,LONG* width,LONG* height) //取出png文件中的rgb数据 { pic_data *out =(pic_data*)malloc(sizeof(pic_data)); png_structp png_ptr; //png文件句柄 png_infop info_ptr;//png图像信息句柄 int ret; FILE *fp; if (check_is_png(&fp, filename) != 0) { LILOG("file is not png ...\n"); return NULL; } png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); info_ptr = png_create_info_struct(png_ptr); setjmp(png_jmpbuf(png_ptr)); rewind(fp); png_init_io(png_ptr, fp); png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0); //读取文件信息 int channels, color_type; channels = png_get_channels(png_ptr, info_ptr); //通道数量 color_type = png_get_color_type(png_ptr, info_ptr);//颜色类型 out->bit_depth = png_get_bit_depth(png_ptr, info_ptr);//位深度 out->width = png_get_image_width(png_ptr, info_ptr);//宽 out->height = png_get_image_height(png_ptr, info_ptr);//高 *width=out->width; *height=out->height; if(color_type == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png_ptr);//要求转换索引颜色到RGB if(color_type == PNG_COLOR_TYPE_GRAY && out->bit_depth bit_depth == 16) png_set_strip_16(png_ptr);//要求位深度强制8bit if(png_get_valid(png_ptr,info_ptr,PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr); if(color_type == PNG_COLOR_TYPE_GRAY || color_type == PNG_COLOR_TYPE_GRAY_ALPHA) png_set_gray_to_rgb(png_ptr);//灰度必须转换成RG int i, j, k; int size, pos = 0; int temp; png_bytepp row_pointers; //实际存储rgb数据的buf row_pointers = png_get_rows(png_ptr, info_ptr); //也可以分别每一行获取png_get_rowbytes(); size = out->width * out->height; //申请内存先计算空间 if (channels == 4 || color_type == PNG_COLOR_TYPE_RGB_ALPHA) { //判断是24位还是32位 out->alpha_flag = HAVE_ALPHA; //记录是否有透明通道 size *= (sizeof(unsigned char) * 4); //size = out->width * out->height * channel out->rgba = (png_bytep)malloc(size); if (NULL == out->rgba) { LILOG("malloc rgba faile ...\n"); png_destroy_read_struct(&png_ptr, &info_ptr, 0); fclose(fp); return NULL; } //从row_pointers里读出实际的rgb数据 for (i = out->height-1; i >0; i --) { for (j = 0; j width; j += 4) { out->rgba[pos++] = row_pointers[i][j+2]; out->rgba[pos++] = row_pointers[i][j+1]; out->rgba[pos++] = row_pointers[i][j+0]; out->rgba[pos++] = row_pointers[i][j+3]; } } } else if (channels == 3 || color_type == PNG_COLOR_TYPE_RGB) { //判断颜色深度是24位还是32位 out->alpha_flag = NOT_HAVE_ALPHA; size *= (sizeof(unsigned char) * 4); out->rgba = (png_bytep)malloc(size); if (NULL == out->rgba) { LILOG("malloc rgba faile ...\n"); png_destroy_read_struct(&png_ptr, &info_ptr, 0); fclose(fp); return NULL; } //从row_pointers里读出实际的rgb数据 temp = (3 * out->width); for (i = 0; i height; i ++) { for (j = 0; j pic_data *out=malloc(sizeof(pic_data)); out->bit_depth=8; out->rgba=pixels; out->alpha_flag=HAVE_ALPHA; out->height=height; out->width=width; png_structp png_ptr; png_infop info_ptr; png_byte color_type; png_bytep * row_pointers; FILE *fp = fopen(png_file_name, "wb"); if (NULL == fp) { LILOG("open failed ...2"); return -1; } //1: 初始化libpng结构体 png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0); if (!png_ptr) { LILOG("png_create_write_struct failed ..."); return -1; } //2: 初始化png_infop结构体， //此结构体包含了图像的各种信息如尺寸，像素位深, 颜色类型等等 info_ptr = png_create_info_struct(png_ptr); if (!info_ptr) { LILOG("png_create_info_struct failed ...\n"); return -1; } //3: 设置错误返回点 if (setjmp(png_jmpbuf(png_ptr))) { LILOG("error during init_io ...\n"); return -1; } //4:绑定文件IO到Png结构体 png_init_io(png_ptr, fp); if (setjmp(png_jmpbuf(png_ptr))) { LILOG("error during init_io ...\n"); return -1; } if (out->alpha_flag == HAVE_ALPHA) color_type = PNG_COLOR_TYPE_RGB_ALPHA; else color_type = PNG_COLOR_TYPE_RGB; //5：设置以及写入头部信息到Png文件 png_set_IHDR(png_ptr, info_ptr, out->width, out->height, out->bit_depth, color_type, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE); png_write_info(png_ptr, info_ptr); if (setjmp(png_jmpbuf(png_ptr))) { LILOG("error during init_io ...\n"); return -1; } int channels, temp; int i, j, pos = 0; if (out->alpha_flag == HAVE_ALPHA) { channels = 4; temp = (4 * out->width); } else { channels = 3; temp = (3 * out->width); } row_pointers = (png_bytep*)malloc(out->height * sizeof(png_bytep)); for (i = out->height-1; i >=0; i--) { row_pointers[i] = (png_bytep)malloc(temp* sizeof(unsigned char)); for (j = 0; j row_pointers[i][j+2] = out->rgba[pos++]; row_pointers[i][j+1] = out->rgba[pos++]; row_pointers[i][j+0] = out->rgba[pos++]; row_pointers[i][j+3] = out->rgba[pos++]; } else { row_pointers[i][j+2] = out->rgba[pos++]; row_pointers[i][j+1] = out->rgba[pos++]; row_pointers[i][j+0] = out->rgba[pos++]; } } } png_write_image(png_ptr, (png_bytepp)row_pointers); if (setjmp(png_jmpbuf(png_ptr))) { return -1; } //7: 写入尾部信息 png_write_end(png_ptr, NULL); //8:释放内存 ,销毁png结构体 for (i = 0; i height; i ++) free(row_pointers[i]); free(row_pointers); png_destroy_write_struct(&png_ptr, &info_ptr); fclose(fp); return 0; } #endif //USE_PNG #endif // !LI_PAINTER_C (四)效果展示 /* * @Descripttion: 底层图片IO测试 * @version: V 2.0 * @Author: Yueyang * @email: [email protected] * @Date: 2020-10-26 19:35:49 * @LastEditors: Yueyang * @LastEditTime: 2020-11-04 15:50:21 */ #include #include #include #include #include "bmp.h" #include "cv.h" #include "li_image.h" int main() { //加载保存销毁图片 Li_Image* out=Li_Load_Image("./picture/whu_rgb888.bmp",LI_BMP_888); Li_Save_Image("./picture/1.bmp",out); Li_Destroy_Image(out); Li_Image* out3=Li_Load_Image("./picture/whu_gray.bmp",LI_BMP_8); Li_Save_Image("./picture/2.bmp",out3); Li_Destroy_Image(out3); Li_Image* out4=Li_Load_Image("./picture/whu_rgba.bmp",LI_BMP_32); Li_Save_Image("./picture/3.bmp",out4); Li_Destroy_Image(out4); Li_Image* out1=Li_Load_Image("./picture/whu_png.png",LI_PNG); Li_Save_Image("./picture/1.png",out1); Li_Destroy_Image(out1); Li_Image* out2=Li_Load_Image("./picture/whu_jpg.jpg",LI_JPEG); Li_Save_Image("./picture/1.jpg",out2); Li_Destroy_Image(out2); //创建图片并操作像素 BYTE* ptr=NULL; Li_Image* out7 =Li_Create_Image(300,300,LI_DEP_24U,LI_BMP_888); ptr=out7->at(out7,10,10); if(ptr!=NULL){ memset(ptr,0xFF,1); memset(ptr+1,0,1); memset(ptr+2,0,1); } Li_Save_Image("./picture/1.bmp",out3); Li_Destroy_Image(out7); Li_Image* out8 =Li_Load_Image("./picture/whu_jpg.jpg",LI_JPEG); ptr=out8->at(out8,10,10); if(ptr!=NULL){ memset(ptr,0xFF,1); memset(ptr+1,0,1); memset(ptr+2,0,1); } Li_Save_Image("./picture/2.jpg",out8); Li_Destroy_Image(out8); Li_Image* out5 =Li_Load_Image("./picture/whu_png.png",LI_PNG); ptr=out5->at(out5,10,10); if(ptr!=NULL){ memset(ptr,0xFF,1); memset(ptr+1,0,1); memset(ptr+2,0,1); } Li_Save_Image("./picture/2.png",out5); Li_Image* out6=Li_Copy_Image(out5); Li_Save_Image("./picture/3.png",out6); LILOG("over"); return 0; }

在这里插入图片描述左边是png图片读取为BMP同时显示，右边是JPEG经过高倍压缩再解压后的图片。

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