[Case Study]C语言实现BMP转换JPG的方法

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1. /****************************************************************************
   
2. 名称：  jpeg.c
   
3. 功能：  linux下bmp转化为jpeg程序源代码
   
4. 日期：  2010.01.26
   
5. 注意：  编译时加“-ljpeg”(gcc -o bmp2jpg jpeg.c -ljpeg)
   
6. *****************************************************************************/
   
7. #include <string.h>
   
8. #include <sys/types.h>
   
9. #include <sys/stat.h>
   
10. #include <sys/ioctl.h>
    
11. #include <sys/mman.h>
    
12. #include <linux/videodev.h>
    
13. #include <fcntl.h>
    
14. #include <unistd.h>
    
15. #include <stdio.h>
    
16. #include <errno.h>
    
17. #include <stdlib.h>
    
18. #include <signal.h>
    
19. #include <sys/timeb.h>
    
20. #include <jpeglib.h>
    
21. #define JPEG_QUALITY 95 //图片质量
    
22. int Bmp2Jpg(const char *bmp_file, const char *jeg_file, const int width, const int height)
    
23. {
    
24.   FILE *fd;
    
25.   int ret;
    
26.   unsigned char *data;
    
27.   long sizeImage;
    
28.   int depth = 3;
    
29.   JSAMPROW * row_pointer;
    
30.   long rgb_index = 0;
    
31.   int i=0;
    
32.   struct jpeg_compress_struct cinfo;
    
33.   struct jpeg_error_mgr jerr;
    
34.   FILE *outfile;            
    
35.   ;
    
36.   // Read bmp image data
    
37.   sizeImage = width*height*3;
    
38.   data = (unsigned char*)malloc(sizeImage);
    
39.   fd = fopen(bmp_file, "rb");
    
40.   if(!fd)
    
41.   {
    
42.     printf("ERROR1: Can not open the image.\n");
    
43.     free(data);
    
44.     return -1;
    
45.   }
    
46.   fseek(fd, 54, SEEK_SET);
    
47.   ret = fread(data, sizeof(unsigned char)*sizeImage, 1, fd);
    
48.   if(ret == 0)
    
49.   {
    
50.     if(ferror(fd))
    
51.     {
    
52.       printf("\nERROR2: Can not read the pixel data.\n");
    
53.       free(data);
    
54.       fclose(fd);
    
55.       return -1;
    
56.     }
    
57.   }
    
58.   //Convert BMP to JPG
    
59.   cinfo.err = jpeg_std_error(&jerr);
    
60.   //* Now we can initialize the JPEG compression object.
    
61.   jpeg_create_compress(&cinfo);
    
62.   if ((outfile = fopen(jeg_file, "wb")) == NULL)
    
63.   {
    
64.     fprintf(stderr, "can't open %s\n", jeg_file);
    
65.     return -1;
    
66.   }
    
67.   jpeg_stdio_dest(&cinfo, outfile);
    
68.   cinfo.image_width = width;
    
69.   //* image width and height, in pixels
    
70.   cinfo.image_height = height;
    
71.   cinfo.input_components = depth;
    
72.   //* # of color components per pixel
    
73.   cinfo.in_color_space = JCS_RGB;
    
74.   //* colorspace of input image
    
75.   jpeg_set_defaults(&cinfo);
    
76.    //Now you can set any non-default parameters you wish to.
    
77.    //Here we just illustrate the use of quality (quantization table) scaling:
    
78.   jpeg_set_quality(&cinfo, JPEG_QUALITY, TRUE );
    
79.   //* limit to baseline-JPEG values
    
80.   jpeg_start_compress(&cinfo, TRUE);
    
81.   //一次写入
    
82.   int j=0;
    
83.   row_pointer = malloc(height*width*3);
    
84.   char * line[300];
    
85.   for(i=0;i<height;i++)
    
86.   {  
    
87.     unsigned char * lineData = NULL;
    
88.     lineData = malloc(width*3);
    
89.     line[i]=lineData;
    
90.     for(j=0;j<width;j++)
    
91.     {
    
92.       lineData[j*3+2] = data[rgb_index];
    
93.       rgb_index ++;
    
94.       lineData[j*3+1] = data[rgb_index];
    
95.       rgb_index ++;
    
96.       lineData[j*3+0] = data[rgb_index];
    
97.       rgb_index ++;
    
98.     }
    
99.     row_pointer[height-i-1] = lineData;   
    
100.   }
     
101.   jpeg_write_scanlines(&cinfo, row_pointer, height);
     
102.   jpeg_finish_compress(&cinfo);
     
103.   jpeg_destroy_compress(&cinfo);
     
104.   for (i=0; i<height; i++)
     
105.   {
     
106.     free(line[i]);
     
107.   }
     
108.   free(row_pointer);
     
109.   free(data);
     
110.   fclose(fd);
     
111.   fclose(outfile);
     
112.   return 0;
     
113. }

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