使用V4L2读取摄像头并在LCD上显示

我的环境是友善之臂的fire3,Ubuntu1604,使用的是uvc免驱摄像头

大致的工作流程如下

一、获取摄像头图片

1、打开摄像头

2、获取摄像头的一些信息,比如支持的格式等等

3、设置摄像头的一些参数,比如输出格式等等

4、申请缓冲区

5、内存映射

6、开始采集

二、将图片在lcd上显示出来

1、打开lcd的设备fb0,如果没有这个,恭喜。

2、获取一些lcd的信息,如lcd的长宽等

3、内存映射

4、将图片写进映射过来的内存。

由于我的摄像头选的是YUYV的输出格式,所以在从摄像头取得图片之后,还需要转换成rgb才行,因为lcd得写rgb才行。

 

下面是代码:

分为主要的摄像头读取文件以及一个framebuffer,lcd的显示文件。

1、摄像头读取文件

头文件

#ifndef _V4L2_H
#define _V4L2_H

#define DEV_PATH "/dev/video0"
#define BMP      "./image.bmp"
#define YUYV     "./image.yuv"

#define TURE 1
#define FALSE 0
#define N_BUFFER 4
struct buffer{
	void* start;
	unsigned int length;
};

/*V4L2初始化*/
void v4l2_init();

/*V4L2关闭*/
void v4l2_close();
#endif

 

C文件

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "V4l2.h"
#include "framebuffer.c"

static int fd;
struct buffer* buffers=NULL;

void v4l2_init(int width,int height){
	/*打开设备*/
	fd=open(DEV_PATH,O_RDWR);
	if(fd==-1)
		perror("open "),exit(-1);
	/*读取设备信息*/
	struct v4l2_capability cap;
	int res=ioctl(fd, VIDIOC_QUERYCAP, &cap);
	if(res==-1)
		printf("read dev information error\n"),exit(-1);
	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);
	}

	/*查询是否支持视频采集*/

	if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE)
		printf("Device %s: supports capture.\n",DEV_PATH);
	else
		printf("Device not supports capture\n"),exit(-1);
	if ((cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING)
		printf("Device %s: supports streaming.\n",DEV_PATH);
	else
		printf("Device not supports streaming\n"),exit(-1);
	
	/*查询设备支持的图片输出格式*/
	struct v4l2_fmtdesc fmtdesc;
	fmtdesc.index=0;
	fmtdesc.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
	printf("Support format:\n");
	while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc)!=-1){
		printf("%d.%s\n",fmtdesc.index+1,fmtdesc.description);
		fmtdesc.index++;
	}

	/*设置帧格式,并检验*/
	struct v4l2_format format;
	format.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
	format.fmt.pix.pixelformat=V4L2_PIX_FMT_YUYV;
	format.fmt.pix.height=height;
	format.fmt.pix.width=width;
	format.fmt.pix.field=V4L2_FIELD_INTERLACED;

	res=ioctl(fd,VIDIOC_S_FMT,&format);
	if(res==-1)
		printf("set up frame foramt failed\n"),exit(-1);

	res=ioctl(fd,VIDIOC_G_FMT,&format);
	if(res==-1)
		printf("read frame format failed\n"),exit(-1);
	
	printf("type:\t\t%d\n",format.type);
    
	printf("pix.pixelformat:\t%c%c%c%c\n",format.fmt.pix.pixelformat & 0xFF, (format.fmt.pix.pixelformat >> 8) & 0xFF,(format.fmt.pix.pixelformat >> 16) & 0xFF, (format.fmt.pix.pixelformat >> 24) & 0xFF);
    
	printf("pix.height:\t\t%d\n",format.fmt.pix.height);
    printf("pix.width:\t\t%d\n",format.fmt.pix.width);
    printf("pix.field:\t\t%d\n",format.fmt.pix.field);

	/*申请缓冲区*/
	struct v4l2_requestbuffers req;
	struct v4l2_buffer buf;

	req.count=N_BUFFER;
	req.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory=V4L2_MEMORY_MMAP;
	res=ioctl(fd,VIDIOC_REQBUFS,&req);
	if(res==-1)
		printf("memory request failed\n"),exit(-1);
	buffers=malloc(req.count*sizeof(struct buffer));

	if(!buffers)
		printf("out of memory!\n"),exit(-1);
	
	for(int i=0;i255) rt0=255;
		else if(rt0<0) rt0=0;
	
		if(gt0>255) gt0=255;
		else if(gt0<0) gt0=0;
		
		if(bt0>255) bt0=255;
		else if(bt0<0) bt0=0;
		
		if(rt1>255) rt1=255;
		else if(rt1<0) rt1=0;
		
		if(gt1>255) gt1=255;
		else if(gt1<0) gt1=0;
		
		if(bt1>255) bt1=255;
		else if(bt1<0) bt1=0;
		*r0=(unsigned char)rt0;
		*g0=(unsigned char)gt0;
		*b0=(unsigned char)bt0;
		*r1=(unsigned char)rt1;
		*g1=(unsigned char)gt1;
		*b1=(unsigned char)bt1;
		
		frame[i1+j1].b=*r0;		
		frame[i1+j1].g=*g0;
		frame[i1+j1].r=*b0;
		frame[i1+j1+1].b=*r1;
		frame[i1+j1+1].g=*g1;
		frame[i1+j1+1].r=*b1;
		j1+=2;
		if(i%320==0){
			j1=0;
			i1+=framex;
		}
		yuv=yuv+4;
		rgb=rgb+6;

		if(yuv==NULL)
			break;

		y0=yuv;
		u0=yuv+1;
		y1=yuv+2;
		v0=yuv+3;

		r0=rgb+0;
		g0=rgb+1;
		b0=rgb+2;
		r1=rgb+3;
		g1=rgb+4;
		b1=rgb+5;
	}
}

void yuyv_to_rgb32(unsigned char* yuv,int length,unsigned char *rgb){
	unsigned int i;
	unsigned char* y0=yuv+0;
	unsigned char* u0=yuv+1;
	unsigned char* y1=yuv+2;
	unsigned char* v0=yuv+3;

	unsigned char* r0=rgb+0;
	unsigned char* g0=rgb+1;
	unsigned char* b0=rgb+2;
	unsigned char* r1=rgb+4;
	unsigned char* g1=rgb+5;
	unsigned char* b1=rgb+6;

	double rt0=0,gt0=0,bt0=0,rt1=0,gt1=0,bt1=0;
	for(i=0;i<=(length/4);i++){
		bt0=1.164*(*y0-16)+2.017*(*u0-128);
		gt0=1.164*(*y0-16)-0.813*(*v0-128)-0.392*(*u0-128);
		rt0=1.164*(*y0-16)+1.596*(*v0-128);

		bt1=1.164*(*y1-16)+2.017*(*u0-128);
		gt1=1.164*(*y1-16)-0.813*(*v0-128)-0.392*(*u0-128);
		rt1=1.164*(*y1-16)+1.596*(*v0-128);

		if(rt0>255) rt0=255;
		else if(rt0<0) rt0=0;
	
		if(gt0>255) gt0=255;
		else if(gt0<0) gt0=0;
		
		if(bt0>255) bt0=255;
		else if(bt0<0) bt0=0;
		
		if(rt1>255) rt1=255;
		else if(rt1<0) rt1=0;
		
		if(gt1>255) gt1=255;
		else if(gt1<0) gt1=0;
		
		if(bt1>255) bt1=255;
		else if(bt1<0) bt1=0;
	
		*r0=(unsigned char)rt0;
		*g0=(unsigned char)gt0;
		*b0=(unsigned char)bt0;
		*r1=(unsigned char)rt1;
		*g1=(unsigned char)gt1;
		*b1=(unsigned char)bt1;
		
		yuv=yuv+4;
		rgb=rgb+8;

		if(yuv==NULL)
			break;

		y0=yuv;
		u0=yuv+1;
		y1=yuv+2;
		v0=yuv+3;

		r0=rgb+0;
		g0=rgb+1;
		b0=rgb+2;
		r1=rgb+4;
		g1=rgb+5;
		b1=rgb+6;
	}
}

int main(){
	struct buffer* yuv=NULL;
	v4l2_init(640,480);
	framebuffer_init();
	void * pic=malloc(640*480*3);	
	while(1){
		yuv=v4l2_get();
		yuyv_to_rgb24(yuv->start,yuv->length,(unsigned char*)pic);
	}
	framebuffer_close();
	v4l2_close();
}

 

 

2、framebuffer文件

头文件

#ifndef _FRAMEBUFFER_H
#define _FRAMEBUFFER_H

typedef struct{
	unsigned char r;
	unsigned char g;
	unsigned char b;
	unsigned char rgbReserved;
}rgb32;

typedef struct{
	unsigned char r;
	unsigned char g;
	unsigned char b;
	unsigned char rgbReserved;
}rgb32_frame;

typedef struct{
	unsigned char r;
	unsigned char g;
	unsigned char b;
}rgb24;

typedef struct{
	unsigned char r;
	unsigned char g;
	unsigned char b;
}rgb24_frame;

void framebuffer_init(void);

void framebuffer_write(void* img_buf,unsigned int img_width,unsigned int img_height,unsigned int img_bits);

void framebuffer_close(void);


#endif

 

 

C文件

#include "framebuffer.h"
#include
#include
#include
#include
#include
#include
#include
#include

static int frame_fd=-1;
void* framebuffer=NULL;
static int screensize=0;
int framex=0;

void framebuffer_init(void){ 
    struct fb_var_screeninfo vinfo;
    struct fb_fix_screeninfo finfo;
    frame_fd = open("/dev/fb0" , O_RDWR);  
    if(frame_fd==-1)  
        perror("open frame buffer fail"),exit(-1);

    // Get fixed screen information
    if (ioctl(frame_fd, FBIOGET_FSCREENINFO, &finfo))
        printf("Error reading fixed information.\n"),exit(-1);
   
	 // Get variable screen information
    if (ioctl(frame_fd, FBIOGET_VSCREENINFO, &vinfo)) 
        printf("Error reading variable information.\n"),exit(-1);
    //这里把整个显存一起初始化(xres_virtual 表示显存的x,比实际的xres大,bits_per_pixel位深)
   
	screensize = vinfo.xres_virtual * vinfo.yres_virtual * vinfo.bits_per_pixel / 8;
    framex=vinfo.xres_virtual;
	//获取实际的位色,这里很关键,后面转换和填写的时候需要
    int framebpp = vinfo.bits_per_pixel;
    printf("%dx%d, %d bpp  screensize is %ld\n", vinfo.xres_virtual, vinfo.yres_virtual, vinfo.bits_per_pixel,screensize);
    
    //映射出来,用户直接操作
    framebuffer = mmap(0, screensize, PROT_READ | PROT_WRITE , MAP_SHARED ,frame_fd ,0 );  
    if(framebuffer == (void *)-1)  
        perror("memory map fail"),exit(-1);    
}



//写入framebuffer   img_buf:采集到的图片首地址  width:用户的宽 height:用户的高  bits:图片的位深 
void framebuffer_write(void *img_buf, unsigned int img_width, unsigned int img_height, unsigned int img_bits){   
    int row, column;
    int num = 0;        //img_buf 中的某个像素点元素的下标
    rgb32_frame *rgb32_fbp = (rgb32_frame *)framebuffer;
    rgb24 *rgb24_img_buf = (rgb24 *)img_buf;    
    
    //防止摄像头采集宽高比显存大
    if(screensize < img_width * img_height * img_bits / 8){
        printf("the imgsize is too large\n"),exit(-1);
    }
    /*不同的位深度图片使用不同的显示方案*/
    switch (img_bits){
        case 24:
            for(row = 0; row < img_height; row++){
                    for(column = 0; column < img_width; column++){
                        //由于摄像头分辨率没有帧缓冲大,完成显示后,需要强制换行,帧缓冲是线性的,使用row * vinfo.xres_virtual换行
                        rgb32_fbp[row * framex + column].r = rgb24_img_buf[num].b;
                        rgb32_fbp[row * framex + column].g = rgb24_img_buf[num].g;
                        rgb32_fbp[row * framex + column].b = rgb24_img_buf[num].r;
                        num++;
                    }        
                }    
            break;
        default:
            break;
    }
}

void framebuffer_close(void){
    munmap(framebuffer,screensize);  
	if(frame_fd==-1)
		perror("file don't exit\n"),exit(-1);
    close(frame_fd);  
}

 

 

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