如何使用 OpenCV 打开摄像头获取图像数据？

OpenCV 如何打开摄像头获取图像数据？

代码运行环境：Qt 5.9.1 msvc2015 32bit OpenCV 3.3.0

#include "include/opencv2/opencv.hpp"
#include <iostream>
using namespace std;
using namespace cv;
int main(int argc, char *argv[])
{
#define 第一个摄像头 0
#define 第二个摄像头 1
#define 第三个摄像头 2
#define Esc 27
//#define 轮廓检测
//#define 灰度化
#define 旋转90度
    cv::VideoCapture capture;
    capture.open(第一个摄像头);
    if(!capture.isOpened())
    {
        return;
    }
    Mat frame;
#ifdef 轮廓检测
    Mat cannyDst;
#endif
//    capture.set(CV_CAP_PROP_FRAME_WIDTH, 1280);
//    capture.set(CV_CAP_PROP_FRAME_HEIGHT, 720);
//    capture.set(CV_CAP_PROP_FRAME_WIDTH, 640);
//    capture.set(CV_CAP_PROP_FRAME_HEIGHT, 480);
//    capture.set(CAP_PROP_FRAME_WIDTH,320);
//    capture.set(CAP_PROP_FRAME_HEIGHT,240);
//    capture.set(CAP_PROP_EXPOSURE,10);//设置曝光率
//    qDebug()<<capture.get(CV_CAP_PROP_FRAME_WIDTH)<<"x"<<capture.get(CV_CAP_PROP_FRAME_HEIGHT);
    double FPS, T;
    while(true)
    {
        T = (double)cv::getTickCount();
        capture >> frame;
        if(frame.empty())
            break;
        T = ((double)cv::getTickCount() - T) / cv::getTickFrequency();
        FPS = 1.0 / T;
        putText(frame, "FPS:"+std::to_string(FPS) , Point(30, 80), FONT_HERSHEY_TRIPLEX ,2, cvScalar(0, 0, 255, 0));//int(frame.rows*0.9)
//        qDebug()<<frame.cols<<"x"<<frame.rows;
#ifdef 旋转90度
        cv::transpose(frame,frame);
        flip(frame, frame, 1);
#endif
#ifdef 灰度化
        cv::cvtColor(frame, frame, CV_BGR2GRAY);
#endif
#ifdef 轮廓检测
    cv::Canny(frame, cannyDst, 0, 50, 3);
    cv::imshow("摄像头",cannyDst);
#else
    cv::imshow("摄像头",frame);
#endif
        //退出循环
        if (waitKey(1) == Esc)
        {
            break;
        }
    }
}