jpg壓縮原理可以參考這篇文章http://hi.baidu.com/tiandsp/item/f5a2dcde6ef1405bd73aae41，我很早以前轉的一篇文章。

　　沒有使用libjpeg的壓縮代碼可以看看這篇文章http://hi.baidu.com/tiandsp/item/9b5843c58a3b4474cfd4f841，也是我很早以前轉的。

　　這次使用libjpeg庫壓縮和上一篇的解壓正好對應起來，有好多函數名稱我都是對稱的起的，所以結合起來看效果更好。

　　和上一篇一樣，只能處理24位和8位的圖像。

　　代碼如下：

#include <iostream> #include <stdio.h> extern "C"{ #include "jpeglib.h" }; #pragma comment(lib,"jpeg.lib") using namespace std;#pragma pack(2) //兩字節對齊，否則bmp_fileheader會占16Byte struct bmp_fileheader {unsigned short bfType; //若不對齊，這個會占4Byteunsigned long bfSize;unsigned short bfReverved1;unsigned short bfReverved2;unsigned long bfOffBits; };struct bmp_infoheader {unsigned long biSize;unsigned long biWidth;unsigned long biHeight;unsigned short biPlanes;unsigned short biBitCount;unsigned long biCompression;unsigned long biSizeImage;unsigned long biXPelsPerMeter;unsigned long biYpelsPerMeter;unsigned long biClrUsed;unsigned long biClrImportant; };FILE *input_file; FILE *output_file;struct bmp_fileheader bfh; struct bmp_infoheader bih;unsigned char *src_buffer; unsigned char *dst_buffer;void read_bmp_header() { fread(&bfh,sizeof(struct bmp_fileheader),1,input_file);fread(&bih,sizeof(struct bmp_infoheader),1,input_file); }void read_bmp_data() {fseek(input_file,bfh.bfOffBits,SEEK_SET);src_buffer=new unsigned char[bih.biWidth*bih.biHeight*bih.biBitCount/8];fread(src_buffer,sizeof(unsigned char)*bih.biWidth*bih.biHeight*bih.biBitCount/8,1,input_file);unsigned long width=bih.biWidth;unsigned long height=bih.biHeight;unsigned short depth=unsigned short(bih.biBitCount/8);unsigned char *src_point;unsigned char *dst_point;dst_buffer=new unsigned char[width*height*depth]; src_point=src_buffer+width*depth*(height-1);dst_point=dst_buffer+width*depth*(height-1);for (unsigned long i=0;i<height;i++){for (unsigned long j=0;j<width*depth;j+=depth){if (depth==1) //處理灰度圖 {dst_point[j]=src_point[j];}if (depth==3) //處理彩色圖 {dst_point[j+2]=src_point[j+0];dst_point[j+1]=src_point[j+1];dst_point[j+0]=src_point[j+2];}}dst_point-=width*depth;src_point-=width*depth;} }void synthese_jpeg() {struct jpeg_compress_struct cinfo;struct jpeg_error_mgr jerr;JSAMPARRAY buffer;unsigned long width=bih.biWidth;unsigned long height=bih.biHeight;unsigned short depth=unsigned short(bih.biBitCount/8);unsigned char *point;cinfo.err=jpeg_std_error(&jerr); //libjpeg各種配置jpeg_create_compress(&cinfo);jpeg_stdio_dest(&cinfo,output_file);cinfo.image_width=width;cinfo.image_height=height;cinfo.input_components=depth;if (depth==1)cinfo.in_color_space=JCS_GRAYSCALE;elsecinfo.in_color_space=JCS_RGB;jpeg_set_defaults(&cinfo);jpeg_set_quality(&cinfo,20,TRUE); //中間的值為壓縮質量，越大質量越好jpeg_start_compress(&cinfo,TRUE);buffer=(*cinfo.mem->alloc_sarray)((j_common_ptr)&cinfo,JPOOL_IMAGE,width*depth,1);point=dst_buffer+width*depth*(height-1);while (cinfo.next_scanline<height){memcpy(*buffer,point,width*depth);jpeg_write_scanlines(&cinfo,buffer,1);point-=width*depth;}jpeg_finish_compress(&cinfo);jpeg_destroy_compress(&cinfo); }int main() {input_file=fopen("lena_gray.bmp","rb");output_file=fopen("lena.jpg","wb");read_bmp_header();read_bmp_data();synthese_jpeg();fclose(input_file);fclose(output_file);delete[] src_buffer;delete[] dst_buffer;cout<<"good job."<<endl;cin.get();return 0; }

轉載于:https://www.cnblogs.com/tiandsp/archive/2012/12/03/2799561.html

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