使用OpenCV和C ++拍摄Keypress上的网络摄像头摘要的屏幕截图

Question

I'm currently getting the webcam feed of my laptop using VideoCapture cap(0) function and then display it in a Mat frame. What I want to do next is whenever I press a key 'c' for example, it takes the screenshot of the frame and save it into a folder as a JPEG image. However I have no idea on how to do so. Help is much needed, thank you.

Answer 1

I have spent several days searching the internet for the right solution with simple keyboard input. Ther was allways some leg / delay while using cv::waitKey.

The solution i have found is with adding Sleep(5) just after the capturing the frame from webcam.

The below example is a combination of different forum threads.

It works without any leg / delay. Windows OS.

Press "q" to capture and save the frame.

There is a webcam feed always present. You can change the sequence to show the captured frame / image.

PS "tipka" - means "key" on the keyboard.

Regards, Andrej

#include <opencv2/opencv.hpp>
#include <iostream>
#include <stdio.h>
#include <windows.h> // For Sleep


using namespace cv;
using namespace std;


int ct = 0; 
char tipka;
char filename[100]; // For filename
int  c = 1; // For filename

int main(int, char**)
{


    Mat frame;
    //--- INITIALIZE VIDEOCAPTURE
    VideoCapture cap;
    // open the default camera using default API
    cap.open(0);
    // OR advance usage: select any API backend
    int deviceID = 0;             // 0 = open default camera   
    int apiID = cv::CAP_ANY;      // 0 = autodetect default API
                                  // open selected camera using selected API
    cap.open(deviceID + apiID);
    // check if we succeeded
    if (!cap.isOpened()) {
        cerr << "ERROR! Unable to open camera\n";
        return -1;
    }
    //--- GRAB AND WRITE LOOP
    cout << "Start grabbing" << endl
        << "Press a to terminate" << endl;
    for (;;)
    {
        // wait for a new frame from camera and store it into 'frame'
        cap.read(frame);

        if (frame.empty()) {
            cerr << "ERROR! blank frame grabbed\n";
            break;
        }


        Sleep(5); // Sleep is mandatory - for no leg!



        // show live and wait for a key with timeout long enough to show images
        imshow("CAMERA 1", frame);  // Window name


        tipka = cv::waitKey(30);


        if (tipka == 'q') {

            sprintf_s(filename, "C:/Images/Frame_%d.jpg", c); // select your folder - filename is "Frame_n"
            cv::waitKey(10); 

            imshow("CAMERA 1", frame);
            imwrite(filename, frame);
            cout << "Frame_" << c << endl;
            c++;
        }


        if (tipka == 'a') {
            cout << "Terminating..." << endl;
            Sleep(2000);
            break;
        }


    }
    // the camera will be deinitialized automatically in VideoCapture destructor
    return 0;
}