网址：http://www.cnblogs.com/darkknightzh/p/4973828.html。未经允许，严禁转载。
参考网站：
http://dev.w3.org/Amaya/libjpeg/example.c
http://www.360doc.com/content/13/0226/15/2036337_268016821.shtml
1. 首先去官网http://www.ijg.org/files/下载源码，下载的是jpegsr9a.zip。
2. 解压后放到E盘根目录，“E:jpeg-9a”下会有很多文件。
3. 将“jconfig.vc”改成“jconfig.h”
4. 将“makefile.vc”中第12行
!include <win32.mak>
改成
!include <C:Program FilesMicrosoft SDKsWindowsv6.0AIncludewin32.mak>
5. 打开vs2013的“VS2013 开发人员命令提示”
6. 定位到E:jpeg-9a。在命令行中输入：
E:
之后输入：
cd jpeg-9a
7. 输入” nmake -f makefile.vc” 生成所需要的libjpeg.lib函数库。
8. 使用时，将“jconfig.h”、“jmorecfg.h”、“jpeglib.h”、“libjpeg.lib”四个文件拷贝到对应的文件夹内。
9. libjpeg.lib是用c语言开发的，
如果在C++程序里使用，需要用extern "C" { }包含一下。如下：
extern "C" { #include "jpeglib.h" }
10. 在“解决方案资源管理器”中“属性页“的”连接器-输入-附加依赖项”内，增加“libjpeg.lib”
11. 从缓冲区生成jpg的程序：
1 void GeneJpegFile(const char* jpegFileName, unsigned char* inputData, 2 int nWidth, int nHeight, int nChannel, int nQuality) 3 { 4 /* This struct contains the JPEG compression parameters and pointers to 5 * working space (which is allocated as needed by the JPEG library). 6 * It is possible to have several such structures, representing multiple 7 * compression/decompression processes, in existence at once. We refer 8 * to any one struct (and its associated working data) as a "JPEG object". 9 */ 10 struct jpeg_compress_struct cinfo; 11 12 /* This struct represents a JPEG error handler. It is declared separately 13 * because applications often want to supply a specialized error handler 14 * (see the second half of this file for an example). But here we just 15 * take the easy way out and use the standard error handler, which will 16 * print a message on stderr and call exit() if compression fails. 17 * Note that this struct must live as long as the main JPEG parameter 18 * struct, to avoid dangling-pointer problems. 19 */ 20 struct jpeg_error_mgr jerr; 21 22 /* More stuff */ 23 FILE *outfile; /* target file */ 24 JSAMPROW row_pointer[1]; /* pointer to JSAMPLE row[s] */ 25 int row_stride; /* physical row width in image buffer */ 26 27 /* Step 1: allocate and initialize JPEG compression object */ 28 29 /* We have to set up the error handler first, in case the initialization 30 * step fails. (Unlikely, but it could happen if you are out of memory.) 31 * This routine fills in the contents of struct jerr, and returns jerr's 32 * address which we place into the link field in cinfo. 33 */ 34 cinfo.err = jpeg_std_error(&jerr); 35 36 /* Now we can initialize the JPEG compression object. */ 37 jpeg_create_compress(&cinfo); /* Now we can initialize the JPEG compression object. */ 38 39 /* Step 2: specify data destination (eg, a file) */ 40 /* Note: steps 2 and 3 can be done in either order. */ 41 42 /* Here we use the library-supplied code to send compressed data to a 43 * stdio stream. You can also write your own code to do something else. 44 * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that 45 * requires it in order to write binary files. 46 */ 47 if ((outfile = fopen(jpegFileName, "wb")) == NULL) 48 { 49 fprintf(stderr, "can't open %s ", jpegFileName); 50 return; 51 } 52 jpeg_stdio_dest(&cinfo, outfile); 53 54 /* Step 3: set parameters for compression */ 55 56 /* First we supply a description of the input image. 57 * Four fields of the cinfo struct must be filled in: 58 */ 59 cinfo.image_width = nWidth; /* image width and height, in pixels */ 60 cinfo.image_height = nHeight; 61 cinfo.input_components = nChannel; /* # of color components per pixel */ 62 63 if (nChannel == 1) 64 { 65 cinfo.in_color_space = JCS_GRAYSCALE; /* colorspace of input image */ 66 } 67 else if (nChannel == 3) 68 { 69 cinfo.in_color_space = JCS_RGB; /* colorspace of input image */ 70 } 71 72 /* Now use the library's routine to set default compression parameters. 73 * (You must set at least cinfo.in_color_space before calling this, 74 * since the defaults depend on the source color space.) 75 */ 76 jpeg_set_defaults(&cinfo); 77 78 // Now you can set any non-default parameters you wish to. 79 // Here we just illustrate the use of quality (quantization table) scaling: 80 jpeg_set_quality(&cinfo, nQuality, TRUE); /* limit to baseline-JPEG values */ 81 82 /* Step 4: Start compressor */ 83 84 /* TRUE ensures that we will write a complete interchange-JPEG file. 85 * Pass TRUE unless you are very sure of what you're doing. 86 */ 87 jpeg_start_compress(&cinfo, TRUE); 88 89 /* Step 5: while (scan lines remain to be written) */ 90 /* jpeg_write_scanlines(...); */ 91 92 /* Here we use the library's state variable cinfo.next_scanline as the 93 * loop counter, so that we don't have to keep track ourselves. 94 * To keep things simple, we pass one scanline per call; you can pass 95 * more if you wish, though. 96 */ 97 row_stride = nWidth * nChannel; /* JSAMPLEs per row in image_buffer */ 98 99 while (cinfo.next_scanline < cinfo.image_height) 100 { 101 /* jpeg_write_scanlines expects an array of pointers to scanlines. 102 * Here the array is only one element long, but you could pass 103 * more than one scanline at a time if that's more convenient. 104 */ 105 row_pointer[0] = &inputData[cinfo.next_scanline * row_stride]; 106 (void)jpeg_write_scanlines(&cinfo, row_pointer, 1); 107 } 108 109 /* Step 6: Finish compression */ 110 jpeg_finish_compress(&cinfo); 111 jpeg_destroy_compress(&cinfo); 112 113 /* After finish_compress, we can close the output file. */ 114 fclose(outfile); 115 }
说明：
1. 灰度图像的话，缓冲区大小就是width*height.
2. RGB图像的话，缓冲区大小是width*height*3，同时，像素排列顺序是RGB RGB RGB RGB…
3. 其他格式的话，cinfo.in_color_space需要改成相应的格式，且row_stride的值估计也需要修改，暂时没有考虑。