Snapshot using command line.

asked 2016-03-18 05:41:55 -0500

Hi Folks.

I am trying to take a snapshot from a usb camera from the command line. I have it kind of working. I want to have 3 different commands: open, snapshot and close. I want to open the camera initially and then take snapshots as I please. However the frame grab seems to close the camera down and so it has to be opened again. Is it possible to use one command to open the camera and then another to grab the frame and another to close the camera and is it possible to grab a frame and leave the camera open? My code is below,

Thanks,

Mark.

include <opencv2 opencv.hpp="">

include <iostream>

using namespace cv; using namespace std;

std::string open_cmd("open"); std::string close_cmd("close"); std::string snapshot_cmd("snap");

int main(int argc, char argv[], char*) { //Open the first webcam plugged in the computer

cv::VideoCapture camera(2);
if (!camera.isOpened())
{
    std::cerr << "ERROR: Could not open camera" << std::endl;
    //return 1;
}


int count;

printf("This program was called with \"%s\".\n", argv[0]);

if (argc > 1)
{
    for (count = 1; count < argc; count++)
    {
        printf("argv[%d] = %s\n", count, argv[count]);
    }
}
else
{
    printf("The command had no other arguments.\n");
}

// return 0;

//Create a window to display the images from the webcam
cv::namedWindow("Webcam", CV_WINDOW_AUTOSIZE);

vector<int> compression_params;
compression_params.push_back(CV_IMWRITE_PNG_COMPRESSION);
compression_params.push_back(9);


//Pick up a new frame and display it until you press a key
while (1)
{
    //This will contain the image from the webcam
    cv::Mat frame;

    //Capture the next frame from the webcam
    camera >> frame;

    //Show the image on the window
    cv::imshow("Webcam", frame);

    std::string input_cmd(argv[1]);

    if (open_cmd.compare(input_cmd) == 0) {
        cv::VideoCapture camera(2);
        cv::imshow("Webcam", frame);
        //return 0;
    }
    else if (snapshot_cmd.compare(input_cmd) == 0) {
        camera >> frame;
        imwrite("MyImage.png", frame, compression_params);
        return 0;
    }
    else if (close_cmd.compare(input_cmd) == 0) {
        camera.release();
        //return 0;
    }


}

//Success. The program accomplished its mission and now it can go
// to the heaven of programs.
return 0;

}

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Comments

" Is it possible to use one command to open the camera and then another to grab the frame and another to close the camera" - this sounds like a broken idea. remember, that you have to do all 3 things in the correct order, to take a snapshot.

also, since imshow() won't work without waitKey(some_millis) , wouldn't you want to use the keypress there, to determine, if your program should take another shot, or shutdown (and close the cam) ?

berak gravatar imageberak ( 2016-03-18 05:49:37 -0500 )edit

Is there a quicker way to get a snapshot? At the moment it is taking about 3 seconds. This will be running in the background so I don't need to see it. imwrite seems to do all the steps(even when I have closed it). Is there a different function that will do just the write?????

Thanks.

Mark123 gravatar imageMark123 ( 2016-03-23 10:27:14 -0500 )edit