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;}