linux---libjpeg使用(jpg to rgb)

一：libjpeg库的编译

下载源码，解压后
./configure --prefix=/xxxx CC=arm-linux-gcc - -host=arm-linux --enable-shared --enable-static
---xxxx为生成动静态裤的目录
----CC为交叉编译器
-----enable-shared ---enable-static 使能动静态库

然后make，
再make install，在xxx目录下生成相应的头文件和库
jconfig.h jerror.h jmorecfg.h jpeglib.h 和 libjpeg.9.so.1.0 libjpeg.a

程序编写
例子为framebuffer jpg图片格式转rgb(565)
test.c
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/mman.h>
#include <linux/fb.h>
#include <stdlib.h>

/////////////////头文件
#include "libinclude/jpeglib.h"
#include "libinclude/jerror.h"

struct fb_var_screeninfo var;
unsigned short *fbp;

//////////////定义结构体
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;

FILE * infile;

int main(int argc ,char **argv)
{
int fd,screen_size,i,j;
unsigned short value;
int pos;
char *rdata;
char *Tbmp[]={"bmp/T1.jpg","bmp/T2.jpg","bmp/T3.jpg","bmp/T4.jpg",
"bmp/T5.jpg","bmp/T6.jpg","bmp/T7.jpg","bmp/T8.jpg","bmp/T9.jpg",
"bmp/T10.jpg","bmp/T11.jpg"};
char Tpos = 0;

fd = open("/dev/fb0",O_RDWR);
if(fd<0)
perror(" open ");
ioctl(fd,FBIOGET_VSCREENINFO,&var);
printf("var x = %d , y = %d bits = %d ..\n",var.xres ,var.yres,var.bits_per_pixel);
screen_size = var.xres *var.yres*var.bits_per_pixel/8;
printf("screen_size is %d\n",screen_size);
fbp = (unsigned short *)mmap(0, screen_size, PROT_WRITE | PROT_READ, MAP_SHARED , fd, 0);
if(!fbp)
goto mmap_err;

////////////////////////////产生相应变量
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_decompress(&cinfo);
while(1)
{

///////////////////打开图片文件
if ((infile = fopen(Tbmp[Tpos], "rb")) == NULL) {

fprintf(stderr, "can't open %s\n", "tu.jpg");
exit(1);
}
Tpos ++;
if(Tpos>=11)
Tpos = 0;

/////////////////获取头信息
jpeg_stdio_src(&cinfo, infile);
jpeg_read_header(&cinfo, TRUE);

////////////////分配内存存储字节
rdata=(char*)calloc(cinfo.image_width*cinfo.image_height*cinfo.num_components,1);

////////////////开始解压
jpeg_start_decompress(&cinfo);
JSAMPROW row_pointer[1];
while (cinfo.output_scanline < cinfo.output_height)
{
row_pointer[0] = & rdata[(cinfo.output_scanline)*cinfo.image_width*cinfo.num_components];
jpeg_read_scanlines(&cinfo,row_pointer ,1);

}
/////////////结束解压
jpeg_finish_decompress(&cinfo);

///////////////framebuffer填充刚才分配的字节
pos = 0;
for(i=0;i<var.yres;i++)
for(j=0;j<var.xres;j++)
{
////////////rgb888 转 rgb565
value= ((rdata[pos]>>3)<<11) |((rdata[pos+1]>>2)<<5) |(rdata[pos+2]>>3);
*(fbp+i*var.xres+j) = value;
pos +=3;
}
sleep(3);
fclose(infile);

}

jpeg_destroy_decompress(&cinfo);

munmap(fbp, screen_size);
close(fd);

return 0;

mmap_err:
perror("mmap\n");
return -1;
}

注：jpg默认解压为rgb888

用过动态库和静态库使用

静态库
此时test.c 目录下有 test.c libjpeg.a
jconfig.h jerror.h jmorecfg.h jpeglib.h

arm-linux-gcc test.c -o test -L./ -ljpeg

生成test放到开发板执行

动态库
此时test.c 目录下有test.c
jconfig.h jerror.h jmorecfg.h jpeglib.h libjpeg.9.so.1.0

arm-linux-gcc test.c -o test -L./ -l:libjpeg.9.so.1.0

把libjpeg.9.so.1.0改为libjpeg.9.so 放到开发板 /usr/lib 目录下

生成test放到开发板执行