OpenCV imwrite无效

Question

I have a simple OpenCV application that takes a video stream from the webcam, and when the spacebar is pressed it captures the current image and freezes on that image. When I try to use the cv::imwrite() method to save the picture to disk, it does not work. The code successfully compiles but it does not save the image. It is returning a false value as well from the call. I am not sure if this is an issue of type of image or something else, but I seem to be stumped.

Here is the code for my current cpp class:

#include <iostream>

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

using namespace std;
using namespace cv;

Mat picture;
char key;

class FacialRec {

};

int main() {
    //Starting the video
    VideoCapture videoCapture(0);

    if (!videoCapture.isOpened()) {
        cout << "Unable to open video file." << endl;
        return 1;
    }

    namedWindow("Webcam", CV_WINDOW_AUTOSIZE);

    while(true) {
        Mat frame;
        videoCapture.retrieve(frame);
        bool success = videoCapture.read(frame);

        if (!success) {
            cout << "Could not read from video file" << endl;
            return 1;
        }

        imshow("Webcam", frame);
        key = waitKey(30);

        if (key == 27) { //escape key pressed: stop program
            cout << "ESC pressed. Program closing..." << endl;
            break;
        }else if (key == ' ') { //spacebar pressed: take a picture
            picture = frame;
            key = -1;

            while (true) {
                imshow("Webcam", picture);

                key = waitKey(30);

                if (key == 27 || key == 32) {
                    cout << "ESC or SPACE pressed. Returning to video..." << endl;
                    break;
                }

                if (key == 115) {
                    //trying to save to current directory
                    bool maybe = imwrite("/testimage.jpg", picture);
                    // maybe bool is always getting value of 0, or false
                   cout << "s was pressed. saving image " << maybe << endl;
                }   
            }
        }

    }

    return 0;
}

Answer 1

You are attempting to write testimage.jpg to the / directory. The executing program probably doesn't have sufficient permissions to write to that directory. Based on your comment, you probably want

//trying to save to current directory
bool maybe = imwrite("./testimage.jpg", picture);

Since . denotes the current working directory.

Answer 2

OpenCV sometimes has problems to write to a .jpg image. Try to change that to .png or .bmp to see if that makes a difference in your case.

If you have further issues with writing images, you can debug them in OpenCV by adding this few lines of code to display them and see if they are valid:

// Create a window for display.
namedWindow( "Display window", WINDOW_AUTOSIZE );

// Show our image inside it.
imshow( "Display window", picture );                   

// Wait for a keystroke in the window
waitKey(0);                                         

Answer 3

A few suggestions.

1. try a different file format.
2. does your IDE defiantly know your target folder / home path directory?
3. Is your image definitely valid? does it show when you imshow()?