NVIDIA Jetson TX1 系列开发教程之十：V4L2+OpenCV2.4.13实现预览、拍照功能

NVIDIA Jetson TX1 系列开发教程之十：V4L2+OpenCV2.4.13实现预览、拍照功能

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• 转载请注明作者和出处：http://blog.csdn.net/u011475210
• 嵌入式平台：NVIDIA Jetson TX1
• 嵌入式系统：Ubuntu16.04
• 虚拟机系统：Ubuntu14.04
• 编者: WordZzzz

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写在前面：
本篇博文主要用来讲解上篇博文中关于V4L2框架的程序部分，并在其基础上实现预览和拍照功能的实现.其中，预览分辨率640*480，用键盘检测来改变标志位，当标志位改变时进行拍照，拍照分辨率1920*1080，随后自动切换回预览模式，肉眼基本看不出切换卡顿。

一、V4L2框架：
V4L2程序是基于标准的V4L2框架来写的，大部分程序注释都已给出，如果还有什么不清楚的地方，可以评论、私信或自行查阅V4L2开发手册。

下图是标准V4L2程序流程图。

博客中的程序，在标准V4L2程序的基础上进一步进行了封装，主要是为了实现拍照与预览模式的切换。

/*
 * v4l2cap.h
 *
 *  Created on: Jul 26, 2017
 *      Author: wordzzzz
 */

#ifndef V4L2CAP_H_
#define V4L2CAP_H_

#include "include.h"

#define CLEAR(x) memset(&(x), 0, sizeof(x))

#define TRUE 1
#define FALSE 0

class V4L2Capture {
public:
    V4L2Capture(char *devName, int width, int height, int width_cap, int height_cap);
    virtual ~V4L2Capture();

    int openDevice();
    int closeDevice();
    int initDevice();
    int initDeviceCap();
    int startCapture();
    int stopCapture();
    int freeBuffers();
    int getFrame(void **,size_t *);
    int backFrame();
    int pre2cap();
    int cap2pre();
    int preBegin();
    int preEnd();

    int initBuffers();

    struct cam_buffer
    {
        void* start;
        unsigned int length;
    };
    char *devName;
    int widthCap;
    int heightCap;
    int width;
    int height;
    int fd_cam;
    cam_buffer *buffers;
    unsigned int n_buffers;
    int frameIndex;
};

#endif /* V4L2CAP_H_ */

/*
 * v4l2cap.cpp
 *
 *  Created on: Jul 26, 2017
 *      Author: wordzzzz
 */

#include "v4l2cap.h"

V4L2Capture::V4L2Capture(char *devName, int width, int height, int width_cap, int height_cap) {
    // TODO Auto-generated constructor stub
    this->devName = devName;
    this->fd_cam = -1;
    this->buffers = NULL;
    this->n_buffers = 0;
    this->frameIndex = -1;
    this->width=width;
    this->height=height;
    this->widthCap=width_cap;
    this->heightCap=height_cap;
}

V4L2Capture::~V4L2Capture() {
    // TODO Auto-generated destructor stub
}

/**********打开设备**********/
int V4L2Capture::openDevice() {
    /*设备的打开*/
    printf("video dev : %s\n", devName);
    fd_cam = open(devName, O_RDWR);
    if (fd_cam < 0) {
        perror("Can't open video device");
    }
    return TRUE;
}

/**********关闭设备**********/
int V4L2Capture::closeDevice() {
    if (fd_cam > 0) {
        int ret = 0;
        if ((ret = close(fd_cam)) < 0) {
            perror("Can't close video device");
        }
        return TRUE;
    } else {
        return FALSE;
    }
}

/**********初始化设备（预览模式）**********/
int V4L2Capture::initDevice() {
    int ret;
    struct v4l2_capability cam_cap;     //显示设备信息
    struct v4l2_cropcap cam_cropcap;    //设置摄像头的捕捉能力
    struct v4l2_fmtdesc cam_fmtdesc;    //查询所有支持的格式：VIDIOC_ENUM_FMT
    struct v4l2_crop cam_crop;          //图像的缩放
    struct v4l2_format cam_format;      //设置摄像头的视频制式、帧格式等

    /* 使用IOCTL命令VIDIOC_QUERYCAP，获取摄像头的基本信息*/
    ret = ioctl(fd_cam, VIDIOC_QUERYCAP, &cam_cap);
    if (ret < 0) {
        perror("Can't get device information: VIDIOCGCAP");
    }
    printf(
            "Driver Name:%s\nCard Name:%s\nBus info:%s\nDriver Version:%u.%u.%u\n",
            cam_cap.driver, cam_cap.card, cam_cap.bus_info,
            (cam_cap.version >> 16) & 0XFF, (cam_cap.version >> 8) & 0XFF,
            cam_cap.version & 0XFF);

    /* 使用IOCTL命令VIDIOC_ENUM_FMT，获取摄像头所有支持的格式*/
    cam_fmtdesc.index = 0;
    cam_fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    printf("Support format:\n");
    while (ioctl(fd_cam, VIDIOC_ENUM_FMT, &cam_fmtdesc) != -1) {
        printf("\t%d.%s\n", cam_fmtdesc.index + 1, cam_fmtdesc.description);
        cam_fmtdesc.index++;
    }

    /* 使用IOCTL命令VIDIOC_CROPCAP，获取摄像头的捕捉能力*/
    cam_cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (0 == ioctl(fd_cam, VIDIOC_CROPCAP, &cam_cropcap)) {
        printf("Default rec:\n\tleft:%d\n\ttop:%d\n\twidth:%d\n\theight:%d\n",
                cam_cropcap.defrect.left, cam_cropcap.defrect.top,
                cam_cropcap.defrect.width, cam_cropcap.defrect.height);
        /* 使用IOCTL命令VIDIOC_S_CROP，获取摄像头的窗口取景参数*/
        cam_crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        cam_crop.c = cam_cropcap.defrect;       //默认取景窗口大小
        if (-1 == ioctl(fd_cam, VIDIOC_S_CROP, &cam_crop)) {
            //printf("Can't set crop para\n");
        }
    } else {
        printf("Can't set cropcap para\n");
    }

    /* 使用IOCTL命令VIDIOC_S_FMT，设置摄像头帧信息*/
    cam_format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    cam_format.fmt.pix.width = width;
    cam_format.fmt.pix.height = height;
    cam_format.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;        //要和摄像头支持的类型对应
    cam_format.fmt.pix.field = V4L2_FIELD_INTERLACED;
    ret = ioctl(fd_cam, VIDIOC_S_FMT, &cam_format);
    if (ret < 0) {
        perror("Can't set frame information");
    }
    /* 使用IOCTL命令VIDIOC_G_FMT，获取摄像头帧信息*/
    cam_format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    ret = ioctl(fd_cam, VIDIOC_G_FMT, &cam_format);
    if (ret < 0) {
        perror("Can't get frame information");
    }
    printf("Current data format information:\n\twidth:%d\n\theight:%d\n",
            cam_format.fmt.pix.width, cam_format.fmt.pix.height);
    return TRUE;
}

/**********初始化设备（拍照模式）**********/
int V4L2Capture::initDeviceCap() {
    int ret;
    struct v4l2_format cam_format;      //设置摄像头的视频制式、帧格式等

    /* 使用IOCTL命令VIDIOC_S_FMT，设置摄像头帧信息*/
    cam_format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    cam_format.fmt.pix.width = widthCap;
    cam_format.fmt.pix.height = heightCap;
    cam_format.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;        //要和摄像头支持的类型对应
    cam_format.fmt.pix.field = V4L2_FIELD_INTERLACED;
    ret = ioctl(fd_cam, VIDIOC_S_FMT, &cam_format);
    if (ret < 0) {
        perror("Can't set frame information");
    }
    /* 使用IOCTL命令VIDIOC_G_FMT，获取摄像头帧信息*/
    cam_format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    ret = ioctl(fd_cam, VIDIOC_G_FMT, &cam_format);
    if (ret < 0) {
        perror("Can't get frame information");
    }
    printf("Current data format information:\n\twidth:%d\n\theight:%d\n",
            cam_format.fmt.pix.width, cam_format.fmt.pix.height);
    return TRUE;
}

/**********申请缓存**********/
int V4L2Capture::initBuffers() {
    int ret;
    /* 使用IOCTL命令VIDIOC_REQBUFS，申请帧缓冲*/
    struct v4l2_requestbuffers req;
    CLEAR(req);
    req.count = 4;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;
    ret = ioctl(fd_cam, VIDIOC_REQBUFS, &req);
    if (ret < 0) {
        perror("Request frame buffers failed");
    }
    if (req.count < 2) {
        perror("Request frame buffers while insufficient buffer memory");
    }
    buffers = (struct cam_buffer*) calloc(req.count, sizeof(*buffers));
    if (!buffers) {
        perror("Out of memory");
    }
    for (n_buffers = 0; n_buffers < req.count; n_buffers++) {
        struct v4l2_buffer buf;
        CLEAR(buf);
        // 查询序号为n_buffers 的缓冲区，得到其起始物理地址和大小
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = n_buffers;
        ret = ioctl(fd_cam, VIDIOC_QUERYBUF, &buf);
        if (ret < 0) {
            printf("VIDIOC_QUERYBUF %d failed\n", n_buffers);
            return FALSE;
        }
        buffers[n_buffers].length = buf.length;
        //printf("buf.length= %d\n",buf.length);
        // 映射内存
        buffers[n_buffers].start = mmap(
                NULL, // start anywhere
                buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd_cam,
                buf.m.offset);
        if (MAP_FAILED == buffers[n_buffers].start) {
            printf("mmap buffer%d failed\n", n_buffers);
            return FALSE;
        }
    }
    return TRUE;
}

/**********释放缓存**********/
int V4L2Capture::freeBuffers() {
    unsigned int i;
    for (i = 0; i < n_buffers; ++i) {
        if (-1 == munmap(buffers[i].start, buffers[i].length)) {
            printf("munmap buffer%d failed\n", i);
            return FALSE;
        }
    }
    free(buffers);
    return TRUE;
}

/**********开始采集**********/
int V4L2Capture::startCapture() {
    unsigned int i;
    for (i = 0; i < n_buffers; i++) {
        struct v4l2_buffer buf;
        CLEAR(buf);
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        if (-1 == ioctl(fd_cam, VIDIOC_QBUF, &buf)) {
            printf("VIDIOC_QBUF buffer%d failed\n", i);
            return FALSE;
        }
    }
    enum v4l2_buf_type type;
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == ioctl(fd_cam, VIDIOC_STREAMON, &type)) {
        printf("VIDIOC_STREAMON error");
        return FALSE;
    }
    return TRUE;
}


/**********停止采集**********/
int V4L2Capture::stopCapture() {
    enum v4l2_buf_type type;
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == ioctl(fd_cam, VIDIOC_STREAMOFF, &type)) {
        printf("VIDIOC_STREAMOFF error\n");
        return FALSE;
    }
    return TRUE;
}

/**********获取图像**********/
int V4L2Capture::getFrame(void **frame_buf, size_t* len) {
    struct v4l2_buffer queue_buf;
    CLEAR(queue_buf);
    queue_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    queue_buf.memory = V4L2_MEMORY_MMAP;
    if (-1 == ioctl(fd_cam, VIDIOC_DQBUF, &queue_buf)) {
        printf("VIDIOC_DQBUF error\n");
        return FALSE;
    }
    //printf("queue_buf.index=%d\n",queue_buf.index);
    //pthread_rwlock_wrlock(&rwlock);
    *frame_buf = buffers[queue_buf.index].start;
    *len = buffers[queue_buf.index].length;
    frameIndex = queue_buf.index;
    //pthread_rwlock_unlock(&rwlock);
    return TRUE;
}

/**********返回队列**********/
int V4L2Capture::backFrame() {
    if (frameIndex != -1) {
        struct v4l2_buffer queue_buf;
        CLEAR(queue_buf);
        queue_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        queue_buf.memory = V4L2_MEMORY_MMAP;
        queue_buf.index = frameIndex;
        if (-1 == ioctl(fd_cam, VIDIOC_QBUF, &queue_buf)) {
            printf("VIDIOC_QBUF error\n");
            return FALSE;
        }
        return TRUE;
    }
    return FALSE;
}

/**********预览切换至拍照**********/
int V4L2Capture::pre2cap() {
    if(V4L2Capture::stopCapture() == FALSE){
        printf("StopCapture fail~~\n");
        exit(2);
    }
    if(V4L2Capture::freeBuffers() == FALSE){
        printf("FreeBuffers fail~~\n");
        exit(2);
    }
    if(V4L2Capture::closeDevice() == FALSE){
        printf("CloseDevice fail~~\n");
        exit(1);
    }
    if(V4L2Capture::openDevice() == FALSE){
        printf("OpenDevice fail~~\n");
        exit(1);
    }
    if(V4L2Capture::initDeviceCap() == FALSE){
        printf("InitDeviceCap fail~~\n");
        exit(1);
    }
    if(V4L2Capture::initBuffers() == FALSE){
        printf("InitBuffers fail~~\n");
        exit(2);
    }
    if(V4L2Capture::startCapture() == FALSE){
        printf("StartCapture fail~~\n");
        exit(2);
    }
    return TRUE;
}

/**********拍照切换至预览**********/
int V4L2Capture::cap2pre() {
    if(V4L2Capture::stopCapture() == FALSE){
        printf("StopCapture fail~~\n");
        exit(2);
    }
    if(V4L2Capture::freeBuffers() == FALSE){
        printf("FreeBuffers fail~~\n");
        exit(2);
    }
    if(V4L2Capture::closeDevice() == FALSE){
        printf("CloseDevice fail~~\n");
        exit(1);
    }
    if(V4L2Capture::openDevice() == FALSE){
        printf("OpenDevice fail~~\n");
        exit(1);
    }
    if(V4L2Capture::initDevice() == FALSE){
        printf("InitDevice fail~~\n");
        exit(1);
    }
    if(V4L2Capture::initBuffers() == FALSE){
        printf("InitBuffers fail~~\n");
        exit(2);
    }
    if(V4L2Capture::startCapture() == FALSE){
        printf("StartCapture fail~~\n");
        exit(2);
    }
    return TRUE;
}

/**********预览开启**********/
int V4L2Capture::preBegin() {
    if(V4L2Capture::openDevice() == FALSE){
        printf("OpenDevice fail~~\n");
        exit(1);
    }
    printf("first~~\n");
    if(V4L2Capture::initDevice() == FALSE){
        printf("InitDevice fail~~\n");
        exit(1);
    }
    printf("second~~\n");
    if(V4L2Capture::initBuffers() == FALSE){
        printf("InitBuffers fail~~\n");
        exit(2);
    }
    printf("third~~\n");
    if(V4L2Capture::startCapture() == FALSE){
        printf("StartCapture fail~~\n");
        exit(2);
    }
    printf("fourth~~\n");
    return TRUE;
}

/**********预览结束**********/
int V4L2Capture::preEnd() {
    if(V4L2Capture::stopCapture() == FALSE){
        printf("StopCapture fail~~\n");
        exit(2);
    }
    if(V4L2Capture::freeBuffers() == FALSE){
        printf("FreeBuffers fail~~\n");
        exit(2);
    }
    if(V4L2Capture::closeDevice() == FALSE){
        printf("CloseDevice fail~~\n");
        exit(1);
    }
    return TRUE;
}

二、键盘检测：
主要实现的功能是通过模拟kbhit功能，实现在线程中完成对键盘的检测功能（检测到‘c’时标志位置1）。

/*
 * pthread.h
 *
 *  Created on: Jul 27, 2017
 *      Author: wordzzzz
 */

#ifndef PTHREAD_H_
#define PTHREAD_H_

#include "include.h"

static __inline
int tty_reset(void);

static __inline
int tty_set(void);

static __inline
int kbhit(void);

void *thread(void *arg);

static struct termios ori_attr, cur_attr;

extern uchar flag;

#endif /* PTHREAD_H_ */

/*
 * pthread.cpp
 *
 *  Created on: Jul 27, 2017
 *      Author: wordzzzz
 */

#include "thread.h"

static __inline
int tty_reset(void)
{
        if (tcsetattr(STDIN_FILENO, TCSANOW, &ori_attr) != 0)
                return -1;

        return 0;
}

static __inline
int tty_set(void)
{

        if ( tcgetattr(STDIN_FILENO, &ori_attr) )
                return -1;

        memcpy(&cur_attr, &ori_attr, sizeof(cur_attr) );
        cur_attr.c_lflag &= ~ICANON;
//        cur_attr.c_lflag |= ECHO;
        cur_attr.c_lflag &= ~ECHO;
        cur_attr.c_cc[VMIN] = 1;
        cur_attr.c_cc[VTIME] = 0;

        if (tcsetattr(STDIN_FILENO, TCSANOW, &cur_attr) != 0)
                return -1;

        return 0;
}

static __inline
int kbhit(void)
{

        fd_set rfds;
        struct timeval tv;
        int retval;

        /* Watch stdin (fd 0) to see when it has input. */
        FD_ZERO(&rfds);
        FD_SET(0, &rfds);
        /* Wait up to five seconds. */
        tv.tv_sec  = 0;
        tv.tv_usec = 0;

        retval = select(1, &rfds, NULL, NULL, &tv);
        /* Don't rely on the value of tv now! */

        if (retval == -1) {
                perror("select()");
                return 0;
        } else if (retval)
                return 1;
        /* FD_ISSET(0, &rfds) will be true. */
        else
                return 0;
        return 0;
}

void *thread(void *arg)
{
    int tty_set_flag;
    tty_set_flag = tty_set();
    while(1) {

        if( kbhit() ) {
            const int key = getchar();
            printf("%c pressed\n", key);
            //检测到'c'则标志位置1
            if(key == 'c')
                flag=1;
            //检测到'q'则退出程序
            if(key == 'q')
                exit(0);
                break;
        } else {
//              fprintf(stderr, "\n");
        }
    }

    if(tty_set_flag == 0)
            tty_reset();
    return 0;
}

三、主函数：
include.h里面包含我们所有用到的头文件。

/*
 * include.h
 *
 *  Created on: Jul 26, 2017
 *      Author: wordzzzz
 */

#ifndef INCLUDE_H_
#define INCLUDE_H_

extern "C" {
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 
#include 
}

#include 
#include 
#include 

#include 
#include 

using namespace std;

#endif /* INCLUDE_H_ */

主函数主要实现预览模式的开启、键盘检测线程开启，预览和拍照模式的切换等功能，总体程序比较简单。

/*
 * main.cpp
 *
 *  Created on: Jul 26, 2017
 *      Author: wordzzzz
 */

#include "include.h"
#include "v4l2cap.h"
#include "thread.h"

#define IMAGEWIDTH_CAP 1920 //拍照分辨率
#define IMAGEHEIGHT_CAP 1080//拍照分辨率

#define IMAGEWIDTH 640      //预览分辨率
#define IMAGEHEIGHT 480     //预览分辨率

#define TRUE 1
#define FALSE 0

uchar flag;

int main()
{
    IplImage* img,* img_cap;
    CvMat cvmat,cvmat_cap;
    double t;
    flag=0;
    unsigned char *frame = NULL;
    unsigned long frameSize = 0;
    string videoDev="/dev/video1";//制定设备号

    V4L2Capture *vcap = new V4L2Capture(const_cast<char*>(videoDev.c_str()),
            IMAGEWIDTH, IMAGEHEIGHT, IMAGEWIDTH_CAP, IMAGEHEIGHT_CAP);
    vcap->preBegin();//预览模式开启

    cvNamedWindow("one",CV_WINDOW_AUTOSIZE);//创建显示窗口

    pthread_t id;
    printf("Main thread id is %d \n",pthread_self());
    if(!pthread_create(&id,NULL,thread,NULL))
    {
    printf("succeed!\n");
    }
    else
    {printf("Fail to Create Thread");
    return -1;
    }

    while(1){
        //如果flag为1，则抓取一张照片
        if(flag == 1){
            vcap->pre2cap();                      //预览模式切换至拍照模式
            //这里多获取几次图像队列，以便得到更高的图像质量（刚打开设备时图像模糊）
            vcap->getFrame((void **) &frame, &frameSize);vcap->backFrame();
            vcap->getFrame((void **) &frame, &frameSize);vcap->backFrame();
            vcap->getFrame((void **) &frame, &frameSize);
            cvmat_cap = cvMat(IMAGEHEIGHT_CAP,IMAGEWIDTH_CAP,CV_8UC3,frame);//CV_8UC3
            img_cap = cvDecodeImage(&cvmat_cap,1);//OpenCV图像解码

            if(!img_cap)    printf("No img_cap\n");
            cvSaveImage("cap.jpg",img_cap);       //保存图片
            cvReleaseImage(&img_cap);             //释放img_cap
            vcap->backFrame();                    //返回队列

            vcap->cap2pre();                      //拍照模式切换至预览模式

            flag = 0;
        }
        t = (double)cvGetTickCount();
        vcap->getFrame((void **) &frame, &frameSize);
        cvmat = cvMat(IMAGEHEIGHT,IMAGEWIDTH,CV_8UC3,frame);//CV_8UC3
        img = cvDecodeImage(&cvmat,1);           //OpenCV图像解码
        if(!img)    printf("No img\n");
        cvShowImage("one",img);                  //显示图片
        cvReleaseImage(&img);                    //释放img
        vcap->backFrame();                       //返回队列
        cvWaitKey(1);                            //没有这句话图像无法显示
        t=(double)cvGetTickCount()-t;
        printf("used time is %gms\n",(t/(cvGetTickFrequency()*1000)));
    }

    pthread_exit(0);                            //退出键盘检测线程

    vcap->preEnd();                             //预览模式结束

    return 0;
}

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