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：

  1 #include<Windows.h>
  2 #include <stdio.h>
  3 #include "jpeglib.h"
  4 #include <setjmp.h>
  5 
  6 
  7 //struct  picture{
  8 // JSAMPLE * image_buffer;    /* Points to large array of R,G,B-order data */
  9 // int image_height;    /* Number of rows in image */
 10 // int image_width;        /* Number of columns in image */
 11 // int quality;
 12 // char *destpath;  
 13 //
 14 //};
 15 
 16 JSAMPLE * image_buffer;    /* Points to large array of R,G,B-order data */
 17 int image_height;    /* Number of rows in image */
 18 int image_width;        /* Number of columns in image */
 19 int quality;
 20 char *destpath; 
 21 
 22 struct my_error_mgr {
 23   struct jpeg_error_mgr pub;    /* "public" fields */
 24 
 25   jmp_buf setjmp_buffer;    /* for return to caller */
 26 };
 27 
 28 typedef struct my_error_mgr * my_error_ptr;
 29 
 30 
 31 METHODDEF(void)
 32 my_error_exit (j_common_ptr cinfo)
 33 {
 34   my_error_ptr myerr = (my_error_ptr) cinfo->err;
 35   (*cinfo->err->output_message) (cinfo);
 36   longjmp(myerr->setjmp_buffer, 1);
 37 }
 38 
 39 
 40 GLOBAL(int)
 41 read_JPEG_file (char * filename)
 42 {
 43 
 44   struct jpeg_decompress_struct cinfo;
 45   struct my_error_mgr jerr;
 46   FILE * infile;        /* source file */
 47   JSAMPARRAY buffer;        /* Output row buffer */
 48   int row_stride;        /* physical row width in output buffer */
 49 
 50   if ((infile = fopen(filename, "rb")) == NULL) {
 51     fprintf(stderr, "can't open %s\n", filename);
 52     return 0;
 53   }
 54   cinfo.err = jpeg_std_error(&jerr.pub);
 55   jerr.pub.error_exit = my_error_exit;
 56   if (setjmp(jerr.setjmp_buffer)) {
 57     jpeg_destroy_decompress(&cinfo);
 58     fclose(infile);
 59     return 0;
 60   }
 61   jpeg_create_decompress(&cinfo);
 62   jpeg_stdio_src(&cinfo, infile);
 63   (void) jpeg_read_header(&cinfo, TRUE);
 64   (void) jpeg_start_decompress(&cinfo);
 65   row_stride = cinfo.output_width * cinfo.output_components;
 66   buffer = (*cinfo.mem->alloc_sarray)
 67         ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
 68 
 69 
 70 
 71   //write
 72   struct jpeg_compress_struct wcinfo;
 73   struct jpeg_error_mgr wjerr;
 74   /* More stuff */
 75   FILE * outfile;        /* target file */
 76   JSAMPROW row_pointer[1];    /* pointer to JSAMPLE row[s] */
 77   int wrow_stride;        /* physical row width in image buffer */
 78 
 79   wcinfo.err = jpeg_std_error(&wjerr);
 80   jpeg_create_compress(&wcinfo);
 81   if ((outfile = fopen(destpath, "wb")) == NULL) {
 82       fprintf(stderr, "can't open %s\n", destpath);
 83       // exit(1);
 84   }
 85   jpeg_stdio_dest(&wcinfo, outfile);
 86   wcinfo.image_width =   image_width>cinfo.image_width?cinfo.image_width:image_width;       /* image width and height, in pixels */
 87   wcinfo.image_height = image_height>cinfo.image_height?cinfo.image_height:image_height;
 88   wcinfo.input_components = 3;        /* # of color components per pixel */
 89   wcinfo.in_color_space = JCS_RGB;     /* colorspace of input image */
 90   jpeg_set_defaults(&wcinfo);
 91   jpeg_set_quality(&wcinfo, quality, TRUE /* limit to baseline-JPEG values */);
 92   jpeg_start_compress(&wcinfo, TRUE);
 93   wrow_stride = image_width * 3;    /* JSAMPLEs per row in image_buffer */
 94 
 95 
 96   
 97   int cmod=cinfo.image_height/wcinfo.image_height;
 98 
 99   while (cinfo.output_scanline < cinfo.output_height) {
100     (void) jpeg_read_scanlines(&cinfo, buffer, 1);
101     if(cinfo.output_scanline%cmod==0)
102      (void) jpeg_write_scanlines(&wcinfo,buffer, 1);
103   }
104 
105 
106   (void) jpeg_finish_decompress(&cinfo);
107   jpeg_destroy_decompress(&cinfo);
108   fclose(infile);
109 
110 
111   jpeg_finish_compress(&wcinfo);
112   jpeg_destroy_compress(&wcinfo);
113   fclose(outfile);
114   return 1;
115 }
116 
117 int main(int argc,  char * argd[]){
118 
119     destpath="D:\\jpeg_123.jpg";
120     image_height =100;
121     image_width=128;
122     quality=100;
123   read_JPEG_file("D:\\123.jpg");
124  // write_JPEG_file("D:\\jpeg_123.jpg",100);
125   system("pause");
126  return 0;
127 }