本文实例讲述了C语言实现BMP转换JPG的方法。分享给大家供大家参考。具体实现方法如下：
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/****************************************************************************
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;
}
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