相机拍摄的图像在OpenCV中为全黑

Question

I am a beginner in OpenCV - Java and trying to learn the basics by capturing an image from camera in laptop. I run the following code in eclipse and I can see the camera light flashing for a second, indicating that it really did start. But the image stored is full black.

import org.opencv.core.*;
import org.opencv.videoio.VideoCapture;
import org.opencv.imgcodecs.*;

public class VideoCap {


    public static void main(String[] args){

        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        VideoCapture camera = new VideoCapture(0);
        if(!camera.isOpened()) {
                    System.out.println("Erro in opening camera");
        }

        else {
            Mat frame = new Mat();
            while(true) {
                if(camera.read(frame)) {
                    System.out.println("Camera obtained");
                    System.out.println("Captured frame width" + frame.width()
                    + " catured frame height " + frame.height() );
                    Imgcodecs.imwrite("cam.jpg", frame);
                    break;                  
                }
            }
        }
        camera.release();
    }
}

No errors on console, What might have gone wrong?

Answer 1

You must change your code like this:

import org.opencv.core.*;
import org.opencv.imgcodecs.Imgcodecs;        
import org.opencv.videoio.VideoCapture;        

public class VideoCap {
    public static void main (String args[]){
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        VideoCapture camera = new VideoCapture(0);

        System.out.println("Welcome to OpenCV " + Core.VERSION);
        if(!camera.isOpened()){
            System.out.println("Error");
        }
        else {
            Mat frame = new Mat();
            camera.read(frame); 
            while(true){
                if (camera.read(frame)){
                    System.out.println("Frame Obtained");
                    System.out.println("Captured Frame Width " + 
                    frame.width() + " Height " + frame.height());
                    Imgcodecs.imwrite("c://capture/camera.jpg", frame);
                    System.out.println("OK");
                    break;
                }
            }   
        }
        camera.release();
    }
}