C语言高级应用---操作linux下V4L2摄像头应用程序

我们都知道，想要驱动linux下的摄像头，其实很简单，照着V4L2的手册一步步来写，很快就可以写出来，但是在写之前我们要注意改变系统的一些配置，使系统支持framebuffer，在dev下产生fb0这样的节点，这样我们才能在linux系统上操作Camera摄像头,framebuffer在之前的博文已经有说过了，这里就不再提了。

有需要了解framebuffer的那么请点击:http://baike.baidu.com/view/3351639.htm

       最重要的，我们需要改一个脚本，在/dev/grub.conf，我们来看看怎么改:

# grub.conf generated by anaconda## Note that you do not have to rerun grub after making changes to this file# NOTICE:  You have a /boot partition.  This means that#          all kernel and initrd paths are relative to /boot/, eg.#          root (hd0,0)#          kernel /vmlinuz-version ro root=/dev/sdb2#          initrd /initrd-[generic-]version.img#boot=/dev/sdbdefault=0timeout=5splashimage=(hd0,0)/grub/splash.xpm.gzhiddenmenutitle CentOS (2.6.32-431.el6.i686)root (hd0,0)kernel /vmlinuz-2.6.32-431.el6.i686 ro root=UUID=2bc12537-d6c1-4e67-b4e5-e9c466205554 nomodeset rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_MD crashkernel=auto LANG=zh_CN.UTF-8 rd_NO_LVM rd_NO_DM rhgb quiet vga=0x318initrd /initramfs-2.6.32-431.el6.i686.img

通常情况下，要让framebuffer生效，要加一句vga=???(这里是参数)，简单介绍一下:

我写vga=0x318就是默认就设置为1024x768x24bpp模式。当然还有其它的模式:如下图，根据自己的系统来配置。

色彩640x400640x480800x6001024x7681280x10241600x12004bits??0x302???8bits0x3000x3010x3030x3050x3070x31C15bits?0x3100x3130x3160x3190x31D16bits?0x3110x3140x3170x31A0x31E24bits?0x3120x3150x3180x31B0x31F32bits??????配置完成以后，我们先来了解一下V4L2的主要功能。

V4L2就使程序有发现设备和操作设备的能力.它主要是用一系列的回调函数来实现这些功能。像设置摄像头的频率、帧频、视频压缩格式和图像参数等等。当然也可以用于其他多媒体的开发，如音频等。

但是此框架只能运行在Linux操作系统之上。v4L2是针对uvc免驱usb设备的编程框架 ，主要用于采集usb摄像头等，编程模式如下：

采集方式

打开视频设备后，可以设置该视频设备的属性，例如裁剪、缩放等。这一步是可选的。在Linux编程中，一般使用ioctl函数来对设备的I/O通道进行管理：

extern int ioctl (int __fd, unsigned long int __request, …) __THROW;__fd：设备的ID，例如刚才用open函数打开视频通道后返回的cameraFd；__request：具体的命令标志符。在进行V4L2开发中，一般会用到以下的命令标志符：VIDIOC_REQBUFS：分配内存VIDIOC_QUERYBUF：把VIDIOC_REQBUFS中分配的数据缓存转换成物理地址VIDIOC_QUERYCAP：查询驱动功能VIDIOC_ENUM_FMT：获取当前驱动支持的视频格式VIDIOC_S_FMT：设置当前驱动的频捕获格式VIDIOC_G_FMT：读取当前驱动的频捕获格式VIDIOC_TRY_FMT：验证当前驱动的显示格式VIDIOC_CROPCAP：查询驱动的修剪能力VIDIOC_S_CROP：设置视频信号的边框VIDIOC_G_CROP：读取视频信号的边框VIDIOC_QBUF：把数据放回缓存队列VIDIOC_DQBUF：把数据从缓存中读取出来VIDIOC_STREAMON：开始视频显示函数VIDIOC_STREAMOFF：结束视频显示函数VIDIOC_QUERYSTD：检查当前视频设备支持的标准，例如PAL或NTSC。这些IO调用，有些是必须的，有些是可选择的。

V4L2操作流程:点击这个网址，说得很详细了，这里不多说。

http://baike.baidu.com/view/5494174.htm

接下来我们来看看实战部分,下面是我自己写的程序接口,可以实现视频采集:

1、project.c

#include <stdio.h>#include <unistd.h>#include <fcntl.h>#include "j-yuv.h"#include "CameralOpt.h"#include "FrameBufferOpt.h"#define    WIDTH   640#define    HIGHT   480int main(void){char yuyv[WIDTH*HIGHT*2];char bmp[WIDTH*HIGHT*3];//set_bmp_header((struct bmp_header_t *)bmp, WIDTH, HIGHT);//初始化摄像头Init_Cameral(WIDTH , HIGHT );//初始化framebufferInit_FrameBuffer(WIDTH , HIGHT ); //开启摄像头Start_Cameral();//采集一张图片int count = 0 ; while(1){Get_Picture(yuyv);yuyv2rgb24(yuyv, bmp, WIDTH, HIGHT);Write_FrameBuffer(bmp);//printf("count:%d \n" , count++);}//关闭摄像头Stop_Cameral();//关闭FramebufferExit_Framebuffer();//退出Exit_Cameral();return 0;}

2、juv.h

#ifndef __JYUV_H#define __JYUV_Htypedef unsigned char  u8;typedef unsigned short u16;typedef unsigned int   u32;#pragma pack(1)//定义bmp头struct bmp_header_t{    u16        magic;    u32       file_size;    u32       RESERVED1;    u32       offset;         //54 bytes 表示54个偏移量    u32       head_num;    //40    u32       width;    u32       height;    u16       color_planes; //1    u16       bit_count;    u32       bit_compression; //0    u32       image_size; //except the size of header    u32       h_resolution;    u32       v_resolution;    u32       color_num;    u32       important_colors;};#pragma pack()void set_bmp_header(struct bmp_header_t * header, u32 width, u32 height);int yuyv2rgb24(u8 *yuyv, u8 *rgb, u32 width, u32 height);#endif /* __JYUV_H */ 

3、juv.c

#include "j-yuv.h"#define BIT_COUNT   24void set_bmp_header(struct bmp_header_t *header, u32 width, u32 height){    header->magic = 0x4d42;    header->image_size = width * height * BIT_COUNT/8;    header->file_size = header->image_size + 54;    header->RESERVED1 = 0;    header->offset = 54;    header->head_num = 40;    header->width = width;    header->height = height;    header->color_planes = 1;    header->bit_count = BIT_COUNT;    header->bit_compression = 0;    header->h_resolution = 0;    header->v_resolution = 0;    header->color_num = 0;    header->important_colors = 0;}//yuyv转rgb24的算法实现int yuyv2rgb24(u8 *yuyv, u8 *rgb, u32 width, u32 height){    u32 i, in, rgb_index = 0;    u8 y0, u0, y1, v1;    int r, g, b;    u32 out = 0, x, y;     for(in = 0; in < width * height * 2; in += 4)    {y0 = yuyv[in+0];u0 = yuyv[in+1];y1 = yuyv[in+2];v1 = yuyv[in+3];for (i = 0; i < 2; i++){if (i)y = y1;elsey = y0;r = y + (140 * (v1-128))/100;  //rg = y - (34 * (u0-128))/100 - (71 * (v1-128))/100; //g b = y + (177 * (u0-128))/100; //bif(r > 255)   r = 255;        if(g > 255)   g = 255;        if(b > 255)   b = 255;       if(r < 0)     r = 0;        if(g < 0)     g = 0;        if(b < 0)     b = 0;y = height - rgb_index/width -1;x = rgb_index%width;rgb[(y*width+x)*3+0] = b;rgb[(y*width+x)*3+1] = g;rgb[(y*width+x)*3+2] = r;rgb_index++;}    }    return 0;}

4、FrameBufferOpt.c

#include "FrameBufferOpt.h"static int Frame_fd ; static int *FrameBuffer = NULL ; static int W , H ;//初始化framebufferint Init_FrameBuffer(int Width , int Higth){W = Width ; H = Higth ; Frame_fd = open("/dev/fb" , O_RDWR);if(-1 == Frame_fd){perror("open frame buffer fail");return -1 ; }//根本就不用CPU搬运   用DMA做为搬运工FrameBuffer = mmap(0, 1280*1024*4 , PROT_READ | PROT_WRITE , MAP_SHARED , Frame_fd ,0 );if(FrameBuffer == (void *)-1){perror("memory map fail");return -2 ;}return 0 ; }//写入framebufferint Write_FrameBuffer(const char *buffer){int row  , col ; char *p = NULL ; for(row = 0 ; row <1024 ; row++){for(col = 0 ; col < 1280 ;  col++){if((row < H)  && (col < W)){p = (char *)(buffer + (row * W+ col ) * 3); FrameBuffer[row*1280+col] = RGB((unsigned char)(*(p+2)),(unsigned char)(*(p+1)),(unsigned char )(*p));}}}return 0 ; }//退出framebufferint Exit_Framebuffer(void){munmap(FrameBuffer ,  W*H*4);close(Frame_fd);return 0 ; }

5、FrameBufferOpt.h

#ifndef  _FRAMEBUFFEROPT_H#define  _FRAMEBUFFEROPT_H#include <stdio.h>#include <fcntl.h>#include <unistd.h>#include <sys/mman.h>#define    RGB(r,g,b)((r<<16)|(g<<8)|b)//初始化ramebufferint Init_FrameBuffer(int Width , int Higth);//写数据到framebufferint Write_FrameBuffer(const char *buffer);//退出framebufferint Exit_Framebuffer(void);#endif //_FRAMEBUFFEROPT_H

6、CameralOpt.h

#ifndef  _CAMERALOPT_H#define  _CAMERALOPT_H#include <stdio.h>#include <linux/videodev2.h>#include <fcntl.h>#include <unistd.h>#include <string.h>#include <stdlib.h>#include <errno.h>#include <sys/mman.h>#define   COUNT  3//初始化摄像头int Init_Cameral(int Width , int Hight);int Exit_Cameral(void); //退出摄像头//摄像头开始采集int Start_Cameral(void);int Stop_Cameral(void);//停止摄像头//获取摄像头的数据int Get_Picture(char *buffer);#endif  //_CAMERALOPT_H

7、CameralOpt.c

#include "CameralOpt.h"int video_fd ; int length ; char *yuv[COUNT] ; struct v4l2_buffer  enqueue  , dequeue ;  //定义出入队的操作结构体成员int Init_Cameral(int Width , int Hight){//参数检查char *videodevname = NULL ; videodevname = "/dev/video0" ; //打开设备video_fd = open(videodevname , O_RDWR);if(-1 == video_fd ){perror("open video device fail");return -1 ; }int i ; int ret ; struct v4l2_format  format ; format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ; format.fmt.pix.width  = Width; format.fmt.pix.height = Hight; format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV ;  //我支持的格式是这个ret = ioctl(video_fd , VIDIOC_S_FMT , &format);if(ret != 0){perror("set video format fail");return -2 ; }//申请buffer,切割成几个部分//3struct v4l2_requestbuffers  requestbuffer ; requestbuffer.count = COUNT ; requestbuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ; requestbuffer.memory = V4L2_MEMORY_MMAP ; ret = ioctl(video_fd , VIDIOC_REQBUFS , &requestbuffer);if(ret != 0){perror("request buffer fail ");return -3  ;}//querybufferstruct v4l2_buffer querybuffer ; querybuffer.type =  V4L2_BUF_TYPE_VIDEO_CAPTURE ; querybuffer.memory = V4L2_MEMORY_MMAP ; for(i = 0 ; i < COUNT ; i++){querybuffer.index = i ; ret = ioctl(video_fd , VIDIOC_QUERYBUF , &querybuffer);if(ret != 0){perror("query buffer fail");return -4 ; }//printf("index:%d length:%d  offset:%d \n" , //querybuffer.index , querybuffer.length , querybuffer.m.offset);length = querybuffer.length ; //将摄像头内存印射到进程的内存地址yuv[i] = mmap(0,querybuffer.length , PROT_READ | PROT_WRITE , MAP_SHARED , video_fd , querybuffer.m.offset );//列队struct v4l2_buffer  queuebuffer ; queuebuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ; queuebuffer.memory =  V4L2_MEMORY_MMAP ; queuebuffer.index = i ; ret = ioctl(video_fd , VIDIOC_QBUF , &queuebuffer);if(ret != 0){perror("queuebuffer fail");return -5 ; }}//初始化入队出队enqueue.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ; dequeue.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ; enqueue.memory = V4L2_MEMORY_MMAP ; dequeue.memory = V4L2_MEMORY_MMAP ; return 0 ; }int Exit_Cameral(void){int i ; for(i = 0 ; i < COUNT ; i++)munmap(yuv+i , length);close(video_fd);return 0 ; }int Start_Cameral(void){//开启摄像头int ret ; int on = 1 ; ret = ioctl(video_fd , VIDIOC_STREAMON , &on);if(ret != 0){perror("start Cameral fail");return -1 ; }return 0 ; }int Stop_Cameral(void){//停止摄像头int ret ; int off= 1 ; ret = ioctl(video_fd , VIDIOC_STREAMOFF, &off);if(ret != 0){perror("stop Cameral fail");return -1 ; }return 0 ;}int Get_Picture(char *buffer){int ret ; //出队ret = ioctl(video_fd , VIDIOC_DQBUF , &dequeue);if(ret != 0){perror("dequeue fail");return -1 ; }//获取图片数据 YUV   yuv[dequeue.index]memcpy(buffer , yuv[dequeue.index] , dequeue.length);//write(yuyv_fd , yuv[dequeue.index] , dequeue.length);enqueue.index = dequeue.index ; ret = ioctl(video_fd , VIDIOC_QBUF , &enqueue);if(ret != 0){perror("enqueue fail");return -2 ; }return 0 ; }

运行结果:楼主本人,长得丑别喷。

画面其实是一直在动的，只是我拍了一张图片而已。