gcc版本：4.5.1
视频协议：V4L2
jpeg压缩库：libjpeg
以上都是开源的，下载安装教程很多，不再赘述
说明：（1）由于libjpeg库的例程中，输入的是RGB24格式的图像，而摄像头只能采集YUYV（YUV：422）格式数据，所以，程序中，有YUYV转换为RGB24的过程，再输入libjpeg中
（2）关于yuyv与rgb24的格式，网上资料很多，自行查阅资料
（3）libjpeg库的输出只能是一个文件，如需将输出到内存中，需要修改libjpeg（这个还不会）
程序如下：
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <linux/types.h>
#include <linux/videodev2.h>
#include <setjmp.h>
#include "jpeglib.h"
//#include "v4l2grab.h"
typedef int BOOL;
#define TRUE 1
#define FALSE 0
#define FILE_VIDEO "/dev/video0"
//#define BMP "image_bmp.bmp"
#define YUV "image_yuv.yuv"
#define JPEG "image_jpeg.jpg"
#define IMAGEWIDTH 320
#define IMAGEHEIGHT 240
static int fd;
static struct v4l2_capability cap;
struct v4l2_fmtdesc fmtdesc;
struct v4l2_format fmt,fmtack;
struct v4l2_streamparm setfps;
struct v4l2_requestbuffers req;
struct v4l2_buffer buf;
enum v4l2_buf_type type;
unsigned char frame_buffer[IMAGEWIDTH*IMAGEHEIGHT*3];
struct buffer
{
void * start;
unsigned int length;
} * buffers;
int init_v4l2(void)
{
int i;
int ret = 0;
//opendev
if ((fd = open(FILE_VIDEO, O_RDWR)) == -1)
{
printf("Error opening V4L interface\n");
return (FALSE);
}
//query cap
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1)
{
printf("Error opening device %s: unable to query device.\n",FILE_VIDEO);
return (FALSE);
}
else
{
printf("driver:\t\t%s\n",cap.driver);
printf("card:\t\t%s\n",cap.card);
printf("bus_info:\t%s\n",cap.bus_info);
printf("version:\t%d\n",cap.version);
printf("capabilities:\t%x\n",cap.capabilities);
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE)
{
printf("Device %s: supports capture.\n",FILE_VIDEO);
}
if ((cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING)
{
printf("Device %s: supports streaming.\n",FILE_VIDEO);
}
}
//emu all support fmt
fmtdesc.index=0;
fmtdesc.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
printf("Support format:\n");
while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc)!=-1)
{
printf("\t%d.%s\n",fmtdesc.index+1,fmtdesc.description);
fmtdesc.index++;
}
//set fmt
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.height = IMAGEHEIGHT;
fmt.fmt.pix.width = IMAGEWIDTH;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
if(ioctl(fd, VIDIOC_S_FMT, &fmt) == -1)
{
printf("Unable to set format\n");
return FALSE;
}
if(ioctl(fd, VIDIOC_G_FMT, &fmt) == -1)
{
printf("Unable to get format\n");
return FALSE;
}
{
printf("fmt.type:\t\t%d\n",fmt.type);
printf("pix.pixelformat:\t%c%c%c%c\n",fmt.fmt.pix.pixelformat & 0xFF, (fmt.fmt.pix.pixelformat >> 8) & 0xFF,(fmt.fmt.pix.pixelformat >> 16) & 0xFF, (fmt.fmt.pix.pixelformat >> 24) & 0xFF);
printf("pix.height:\t\t%d\n",fmt.fmt.pix.height);
printf("pix.width:\t\t%d\n",fmt.fmt.pix.width);
printf("pix.field:\t\t%d\n",fmt.fmt.pix.field);
}
//set fps
setfps.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
setfps.parm.capture.timeperframe.numerator = 10;
setfps.parm.capture.timeperframe.denominator = 10;
printf("init %s \t[OK]\n",FILE_VIDEO);
return TRUE;
}
int v4l2_grab(void)
{
unsigned int n_buffers;
//request for 4 buffers
req.count=4;
req.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory=V4L2_MEMORY_MMAP;
if(ioctl(fd,VIDIOC_REQBUFS,&req)==-1)
{
printf("request for buffers error\n");
}
//mmap for buffers
buffers = malloc(req.count*sizeof (*buffers));
if (!buffers)
{
printf ("Out of memory\n");
return(FALSE);
}
for (n_buffers = 0; n_buffers < req.count; n_buffers++)
{
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;
//query buffers
if (ioctl (fd, VIDIOC_QUERYBUF, &buf) == -1)
{
printf("query buffer error\n");
return(FALSE);
}
buffers[n_buffers].length = buf.length;
//map
buffers[n_buffers].start = mmap(NULL,buf.length,PROT_READ |PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
if (buffers[n_buffers].start == MAP_FAILED)
{
printf("buffer map error\n");
return(FALSE);
}
}
//queue
for (n_buffers = 0; n_buffers < req.count; n_buffers++)
{
buf.index = n_buffers;
ioctl(fd, VIDIOC_QBUF, &buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
ioctl (fd, VIDIOC_STREAMON, &type);
ioctl(fd, VIDIOC_DQBUF, &buf);
printf("grab yuyv OK\n");
return(TRUE);
}
int yuyv_2_rgb888(void)
{
int i,j;
unsigned char y1,y2,u,v;
int r1,g1,b1,r2,g2,b2;
char * pointer;
pointer = buffers[0].start;
for(i=0;i<IMAGEHEIGHT;i++)
{
for(j=0;j<IMAGEWIDTH/2;j++)//每次取4个字节，也就是两个像素点，转换rgb，6个字节，还是两个像素点
{
y1 = *( pointer + (i*IMAGEWIDTH/2+j)*4);
u = *( pointer + (i*IMAGEWIDTH/2+j)*4 + 1);
y2 = *( pointer + (i*IMAGEWIDTH/2+j)*4 + 2);
v = *( pointer + (i*IMAGEWIDTH/2+j)*4 + 3);
r1 = y1 + 1.042*(v-128);
g1 = y1 - 0.34414*(u-128) - 0.71414*(v-128);
b1 = y1 + 1.772*(u-128);
r2 = y2 + 1.042*(v-128);
g2 = y2 - 0.34414*(u-128) - 0.71414*(v-128);
b2 = y2 + 1.772*(u-128);
if(r1>255)
r1 = 255;
else if(r1<0)
r1 = 0;
if(b1>255)
b1 = 255;
else if(b1<0)
b1 = 0;
if(g1>255)
g1 = 255;
else if(g1<0)
g1 = 0;
if(r2>255)
r2 = 255;
else if(r2<0)
r2 = 0;
if(b2>255)
b2 = 255;
else if(b2<0)
b2 = 0;
if(g2>255)
g2 = 255;
else if(g2<0)
g2 = 0;
*(frame_buffer + (i*IMAGEWIDTH/2+j)*6 ) = (unsigned char)b1;
*(frame_buffer + (i*IMAGEWIDTH/2+j)*6 + 1) = (unsigned char)g1;
*(frame_buffer + (i*IMAGEWIDTH/2+j)*6 + 2) = (unsigned char)r1;
*(frame_buffer + (i*IMAGEWIDTH/2+j)*6 + 3) = (unsigned char)b2;
*(frame_buffer + (i*IMAGEWIDTH/2+j)*6 + 4) = (unsigned char)g2;
*(frame_buffer + (i*IMAGEWIDTH/2+j)*6 + 5) = (unsigned char)r2;
}
}
printf("change to RGB OK \n");
}
BOOL encode_jpeg(char *lpbuf,int width,int height)
{
struct jpeg_compress_struct cinfo ;
struct jpeg_error_mgr jerr ;
JSAMPROW row_pointer[1] ;
int row_stride ;
char *buf=NULL ;
int x ;
FILE *fptr_jpg = fopen (JPEG,"wb");//注意这里为什么用fopen而不用open
if(fptr_jpg==NULL)
{
printf("Encoder:open file failed!/n") ;
return FALSE;
}
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
jpeg_stdio_dest(&cinfo, fptr_jpg);
cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, 80,TRUE);
jpeg_start_compress(&cinfo, TRUE);
row_stride = width * 3;
buf=malloc(row_stride) ;
row_pointer[0] = buf;
while (cinfo.next_scanline < height)
{
for (x = 0; x < row_stride; x+=3)
{
buf[x] = lpbuf[x];
buf[x+1] = lpbuf[x+1];
buf[x+2] = lpbuf[x+2];
}
jpeg_write_scanlines (&cinfo, row_pointer, 1);//critical
lpbuf += row_stride;
}
jpeg_finish_compress(&cinfo);
fclose(fptr_jpg);
jpeg_destroy_compress(&cinfo);
free(buf) ;
return TRUE ;
}
int close_v4l2(void)
{
if(fd != -1)
{
close(fd);
return (TRUE);
}
return (FALSE);
}
int main(void)
{
FILE * fp2;
if(init_v4l2() == FALSE)
{
return(FALSE);
}
v4l2_grab();
yuyv_2_rgb888(); //yuyv to RGB24
encode_jpeg(frame_buffer,IMAGEWIDTH,IMAGEHEIGHT); //RGB24 to Jpeg
printf("save "JPEG"OK\n");
close_v4l2();
return(TRUE);
}
参考博文：
http://www.cnblogs.com/surpassal/archive/2012/12/19/zed_webcam_lab1.html
http://blog.csdn.net/xingyu19871124/article/details/5517796