Video4linux（v4l）摄像头采集jpeg图片
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1、Video4linux下视频编程的流程 2、为程序定义的数据结构 typedef struct v4l_struct
{
int fd;
struct video_capability capability;
struct video_channel channel[4];
struct video_picture picture;
struct video_window window;
struct video_capture capture;
struct video_buffer buffer;
struct video_mmap mmap;
struct video_mbuf mbuf;
unsigned char *map;
int frame;
int framestat[2];
}vd;
3、Video4linux支持的数据结构及其用途 struct video_capability
{
char name[32];
int type;
int channels; /* Num channels */
int audios; /* Num audio devices */
int maxwidth; /* Supported width */
int maxheight; /* And height */
int minwidth; /* Supported width */
int minheight; /* And height */
};
struct video_channel
{
int channel;
char name[32];
int tuners;
__u32 flags;
#define VIDEO_VC_TUNER 1 /* Channel has a tuner */
#define VIDEO_VC_AUDIO 2 /* Channel has audio */
__u16 type;
#define VIDEO_TYPE_TV 1
#define VIDEO_TYPE_CAMERA 2
__u16 norm; /* Norm set by channel */
};
struct video_picture
{
__u16 brightness;
__u16 hue;
__u16 colour;
__u16 contrast;
__u16 whiteness; /* Black and white only */
__u16 depth; /* Capture depth */
__u16 palette; /* Palette in use */
#define VIDEO_PALETTE_GREY 1 /* Linear greyscale */
#define VIDEO_PALETTE_HI240 2 /* High 240 cube (BT848) */
#define VIDEO_PALETTE_RGB565 3 /* 565 16 bit RGB */
#define VIDEO_PALETTE_RGB24 4 /* 24bit RGB */
#define VIDEO_PALETTE_RGB32 5 /* 32bit RGB */
#define VIDEO_PALETTE_RGB555 6 /* 555 15bit RGB */
#define VIDEO_PALETTE_YUV422 7 /* YUV422 capture */
#define VIDEO_PALETTE_YUYV 8
#define VIDEO_PALETTE_UYVY 9 /* The great thing about standards is ... */
#define VIDEO_PALETTE_YUV420 10
#define VIDEO_PALETTE_YUV411 11 /* YUV411 capture */
#define VIDEO_PALETTE_RAW 12 /* RAW capture (BT848) */
#define VIDEO_PALETTE_YUV422P 13 /* YUV 4:2:2 Planar */
#define VIDEO_PALETTE_YUV411P 14 /* YUV 4:1:1 Planar */
#define VIDEO_PALETTE_YUV420P 15 /* YUV 4:2:0 Planar */
#define VIDEO_PALETTE_YUV410P 16 /* YUV 4:1:0 Planar */
#define VIDEO_PALETTE_PLANAR 13 /* start of planar entries */
#define VIDEO_PALETTE_COMPONENT 7 /* start of component entries */
};
struct video_window
{
__u32 x,y; /* Position of window */
__u32 width,height; /* Its size */
__u32 chromakey;
__u32 flags;
struct video_clip *clips; /* Set only */
int clipcount;
#define VIDEO_WINDOW_INTERLACE 1
#define VIDEO_WINDOW_CHROMAKEY 16 /* Overlay by chromakey */
#define VIDEO_CLIP_BITMAP -1
/* bitmap is 1024x625, a '1' bit represents a clipped pixel */
#define VIDEO_CLIPMAP_SIZE (128 * 625)
};
struct video_capture
{
__u32 x,y; /* Offsets into image */
__u32 width, height; /* Area to capture */
__u16 decimation; /* Decimation divider */
__u16 flags; /* Flags for capture */
#define VIDEO_CAPTURE_ODD 0 /* Temporal */
#define VIDEO_CAPTURE_EVEN 1
};
struct video_buffer
{
void *base;
int height,width;
int depth;
int bytesperline;
};
struct video_mmap
{
unsigned int frame; /* Frame (0 - n) for double buffer */
int height,width;
unsigned int format; /* should be VIDEO_PALETTE_* */
};
#define VIDEO_MAX_FRAME 32
struct video_mbuf
{
int size; /* Total memory to map */
int frames; /* Frames */
int offsets[VIDEO_MAX_FRAME];
};
这些struct都来自videodev.h 4、安装libjpeg 5、使用v4l的摄像头采集jpeg图像的代码： #include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/videodev.h>
#include <jpeglib.h>
#define WIDTH 320
#define HEIGHT 240
#define V4L_DEVICE "/dev/video0"
int write_jpeg(char *filename,unsigned char *buf,int quality,int width, int height, int gray)
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE *fp;
int i;
unsigned char *line;
int line_length;
if (NULL == (fp = fopen(filename,"w")))
{
fprintf(stderr,"grab: can't open %s: %s\n", filename, strerror(errno));
return -1;
}
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);
jpeg_stdio_dest(&cinfo, fp);
cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = gray ? 1: 3;
cinfo.in_color_space = gray ? JCS_GRAYSCALE: JCS_RGB;
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, quality, TRUE);
jpeg_start_compress(&cinfo, TRUE);
line_length = gray ? width : width * 3;
for (i = 0, line = buf; i < height; i++, line += line_length)
jpeg_write_scanlines(&cinfo, &line, 1);
jpeg_finish_compress(&(cinfo));
jpeg_destroy_compress(&(cinfo));
fclose(fp);
return 0;
}
int main()
{
unsigned char* buf;
int i,j;
int fd;
int re;
struct video_capability vcap;
struct video_channel vc;
struct video_mbuf mbuf;
struct video_mmap map;
fd = open(V4L_DEVICE, O_RDWR);
if(fd<=0)
{
perror("open");
exit(1);
}
if(ioctl(fd, VIDIOCGCAP, &vcap)<0)
{
perror("VIDIOCGCAP");
exit(1);
}
printf("Video Capture Device Name : %s\n",vcap.name);
for(i=0;i<vcap.channels;i++)
{
vc.channel = i;
if(ioctl(fd, VIDIOCGCHAN, &vc)<0)
{
perror("VIDIOCGCHAN");
exit(1);
}
printf("Video Source (%d) Name : %s\n",i, vc.name);
}
vc.channel=0;
if(ioctl(fd, VIDIOCSCHAN, &vc) < 0)
{
perror("VIDIOCSCHAN");
exit(1);
}
if(ioctl(fd, VIDIOCGMBUF, &mbuf) < 0)
{
perror("VIDIOCGMBUF");
exit(1);
}
buf=(unsigned char *)mmap(0,mbuf.size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
if((int)buf < 0)
{
perror("mmap");
exit(1);
}
map.frame = 0;
map.height = HEIGHT;
map.width = WIDTH;
map.format = VIDEO_PALETTE_RGB24;
if(ioctl(fd, VIDIOCMCAPTURE, &map)<0)
{
perror("VIDIOCMCAPTURE");
exit(1);
}
if(ioctl(fd, VIDIOCSYNC, &map.frame)<0)
{
perror("VIDIOCSYNC");
exit(1);
}
if(-1==(write_jpeg("./pic001.jpeg",buf,75,WIDTH,HEIGHT,0)))
{
printf("write_jpeg error\n");
exit(1);
}
munmap(buf,mbuf.size);
close(fd);
return 0;
}
v4l编程的详细介绍：http://blog.csdn.net/luxiaoxun/archive/2011/05/27/6450783.aspx |