C语言实现BMP转换JPG的方法

/****************************************************************************
名称：  jpeg.c
功能：  linux下bmp转化为jpeg程序源代码
日期：  2010.01.26
注意：  编译时加“-ljpeg”(gcc -o bmp2jpg jpeg.c -ljpeg)
*****************************************************************************/
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/timeb.h>
#include <jpeglib.h>
#define JPEG_QUALITY 95 //图片质量
int Bmp2Jpg(const char *bmp_file, const char *jeg_file, const int width, const int height)
{
  FILE *fd;
  int ret;
  unsigned char *data;
  long sizeImage;
  int depth = 3;
  JSAMPROW * row_pointer;
  long rgb_index = 0;
  int i=0;
  struct jpeg_compress_struct cinfo;
  struct jpeg_error_mgr jerr;
  FILE *outfile;            
  ;
  // Read bmp image data
  sizeImage = width*height*3;
  data = (unsigned char*)malloc(sizeImage);
  fd = fopen(bmp_file, "rb");
  if(!fd)
  {
    printf("ERROR1: Can not open the image.\n");
    free(data);
    return -1;
  }
  fseek(fd, 54, SEEK_SET); 
  ret = fread(data, sizeof(unsigned char)*sizeImage, 1, fd);
  if(ret == 0)
  {
    if(ferror(fd))
    {
      printf("\nERROR2: Can not read the pixel data.\n");
      free(data);
      fclose(fd);
      return -1;
    }
  }
  //Convert BMP to JPG
  cinfo.err = jpeg_std_error(&jerr);
  //* Now we can initialize the JPEG compression object.
  jpeg_create_compress(&cinfo);
  if ((outfile = fopen(jeg_file, "wb")) == NULL)
  {
    fprintf(stderr, "can't open %s\n", jeg_file);
    return -1;
  }
  jpeg_stdio_dest(&cinfo, outfile);
  cinfo.image_width = width;
  //* image width and height, in pixels
  cinfo.image_height = height;
  cinfo.input_components = depth;
  //* # of color components per pixel
  cinfo.in_color_space = JCS_RGB;
  //* colorspace of input image
  jpeg_set_defaults(&cinfo);
   //Now you can set any non-default parameters you wish to.
   //Here we just illustrate the use of quality (quantization table) scaling:
  jpeg_set_quality(&cinfo, JPEG_QUALITY, TRUE );
  //* limit to baseline-JPEG values
  jpeg_start_compress(&cinfo, TRUE);
  //一次写入
  int j=0;
  row_pointer = malloc(height*width*3);
  char * line[300];
  for(i=0;i<height;i++)
  {  
    unsigned char * lineData = NULL;
    lineData = malloc(width*3);
    line[i]=lineData;
    for(j=0;j<width;j++)
    {
      lineData[j*3+2] = data[rgb_index];
      rgb_index ++;
      lineData[j*3+1] = data[rgb_index];
      rgb_index ++;
      lineData[j*3+0] = data[rgb_index];
      rgb_index ++;
    }
    row_pointer[height-i-1] = lineData;   
  }
  jpeg_write_scanlines(&cinfo, row_pointer, height);
  jpeg_finish_compress(&cinfo);
  jpeg_destroy_compress(&cinfo);
  for (i=0; i<height; i++)
  {
    free(line[i]);
  } 
  free(row_pointer);
  free(data); 
  fclose(fd);
  fclose(outfile);
  return 0;
}