ijg库的使用的几点注意

ijg库（http://www.ijg.org/）是用于处理jpeg解码和压缩的库，最新版本为2014发布的版本,可以在官网中下载jpegsr9a.zip

使用vs中个nmake 进行编译，对于这个版本的库，在编译的时候需要注意这几个点：

1.  可以在cmd中使用命令进行编译（前提是，将 nmake的路径配置到环境变量中path下了）形如：

设置三个变量：

变量名              变量值

include             D:\Program Files\Microsoft Visual Studio 10.0\VC\include\

lib　　　　　　   D:\Program Files\Microsoft Visual Studio 10.0\VC\lib\

path                 D:\Program Files\Microsoft Visual Studio 10.0\VC\bin\

设置好这些变量之后，nmake就可以在cmd中使用了.  进入到ijg源码文件夹中，然后运行

输入    nmake -f   makefile.vc setup-v10   编译，

（1）一般情况下，这个版本都会出现一个“无法找到文件 win32.mak”,将

#include<win32.mak>注释掉就可以了(这个注释，！include<win32.mak>)

（2）再次输入上述的命令，会出现ren jconfig.vc jconfig.h  无法找到 返回0x01的情况

这时候，新建一个jconfig.h文件，将jconfig.txt中的文件原封不动的移入到这个新建的文件中即可.

(3)再次运行上述的命令，便可以成功了！

这样就可以生成windows下的vcproject工程文件了，然后使用vs打开jpeg.pxxxx 即可运行生成静态库jpeg.lib，然后取出文件中的  这几个三个头文件

jconfig.h, jpeglib.h,jmorecfg.h 和jpeg.lib就可以了.

#progma comment("lib","jpeg.lib") //使用这条宏引入静态库即可使用:

下面是一个例子：

 #include<Windows.h>
 #include <stdio.h>
 #include "jpeglib.h"
 #include <setjmp.h>

 //struct  picture{
 // JSAMPLE * image_buffer;    /* Points to large array of R,G,B-order data */
 // int image_height;    /* Number of rows in image */
 // int image_width;        /* Number of columns in image */
 // int quality;
 // char *destpath;
 //
 //};

 JSAMPLE * image_buffer;    /* Points to large array of R,G,B-order data */
 int image_height;    /* Number of rows in image */
 int image_width;        /* Number of columns in image */
 int quality;
 char *destpath; 

 struct my_error_mgr {
   struct jpeg_error_mgr pub;    /* "public" fields */

   jmp_buf setjmp_buffer;    /* for return to caller */
 };

 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, );
 }

 GLOBAL(int)
 read_JPEG_file (char * filename)
 {

   struct jpeg_decompress_struct cinfo;
   struct my_error_mgr jerr;
   FILE * infile;        /* source file */
   JSAMPARRAY buffer;        /* Output row buffer */
   int row_stride;        /* physical row width in output buffer */

   if ((infile = fopen(filename, "rb")) == NULL) {
     fprintf(stderr, "can't open %s\n", filename);
     return ;
   }
   cinfo.err = jpeg_std_error(&jerr.pub);
   jerr.pub.error_exit = my_error_exit;
   if (setjmp(jerr.setjmp_buffer)) {
     jpeg_destroy_decompress(&cinfo);
     fclose(infile);
     return ;
   }
   jpeg_create_decompress(&cinfo);
   jpeg_stdio_src(&cinfo, infile);
   (void) jpeg_read_header(&cinfo, TRUE);
   (void) jpeg_start_decompress(&cinfo);
   row_stride = cinfo.output_width * cinfo.output_components;
   buffer = (*cinfo.mem->alloc_sarray)
         ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, );

   //write
   struct jpeg_compress_struct wcinfo;
   struct jpeg_error_mgr wjerr;
   /* More stuff */
   FILE * outfile;        /* target file */
   JSAMPROW row_pointer[];    /* pointer to JSAMPLE row[s] */
   int wrow_stride;        /* physical row width in image buffer */

   wcinfo.err = jpeg_std_error(&wjerr);
   jpeg_create_compress(&wcinfo);
   if ((outfile = fopen(destpath, "wb")) == NULL) {
       fprintf(stderr, "can't open %s\n", destpath);
       // exit(1);
   }
   jpeg_stdio_dest(&wcinfo, outfile);
   wcinfo.image_width =   image_width>cinfo.image_width?cinfo.image_width:image_width;       /* image width and height, in pixels */
   wcinfo.image_height = image_height>cinfo.image_height?cinfo.image_height:image_height;
   wcinfo.input_components = ;        /* # of color components per pixel */
   wcinfo.in_color_space = JCS_RGB;     /* colorspace of input image */
   jpeg_set_defaults(&wcinfo);
   jpeg_set_quality(&wcinfo, quality, TRUE /* limit to baseline-JPEG values */);
   jpeg_start_compress(&wcinfo, TRUE);
   wrow_stride = image_width * ;    /* JSAMPLEs per row in image_buffer */

   int cmod=cinfo.image_height/wcinfo.image_height;

   while (cinfo.output_scanline < cinfo.output_height) {
     (void) jpeg_read_scanlines(&cinfo, buffer, );
     if(cinfo.output_scanline%cmod==)
      (void) jpeg_write_scanlines(&wcinfo,buffer, );
   }

   (void) jpeg_finish_decompress(&cinfo);
   jpeg_destroy_decompress(&cinfo);
   fclose(infile);

   jpeg_finish_compress(&wcinfo);
   jpeg_destroy_compress(&wcinfo);
   fclose(outfile);
   return ;
 }

 int main(int argc,  char * argd[]){

     destpath="D:\\jpeg_123.jpg";
     image_height =;
     image_width=;
     quality=;
   read_JPEG_file("D:\\123.jpg");
  // write_JPEG_file("D:\\jpeg_123.jpg",100);
   system("pause");
  return ;
 }