OpenCV-Java：VideoCapture读取框架与USB摄像机挂在一起

Question

I'm quite new to OpenCV - Java programming, and I'm trying to setup an application to read video frames from USB WebCam, to start with something.

This is the document I followed up to now: https://opencv-java-tutorials.readthedocs.io/en/latest/03-first-javafx-application-with-opencv.html#video-capturing

The setup is the following:

• Java version: 10.0.1
• OpenCV Version: 3.3.4 and 3.2.0, same error with both versions
• OS: Windows 10 x64
• The .dll is placed under C:\\Windows, that is included in my java.library.path

I have some additional frameworks involved in the application, but I prepared an isolated test case to better check the issue:

import org.junit.Test;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.videoio.VideoCapture;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class CVCaptureTest {

    private static final Logger LOG = LoggerFactory.getLogger(CVCaptureTest.class);

    @Test
    public void testFrameRead() {
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        VideoCapture capture = new VideoCapture();
        capture.open(0);

        for (int i = 0; i < 100; i ++) {
            if (capture.isOpened()) {
                Mat frame = new Mat();
                LOG.info("Capture open. Reading frame...");
                capture.retrieve(frame);

                LOG.info("Captured: {}", frame.dump());
            }
        }
    }
}

Output:

[INFO] Running i.m.r.b.r.c.CVCaptureTest
20:15:57.757 [main] INFO i.m.r.b.r.c.CVCaptureTest - Capture open. Reading frame...

After this log line the program just hangs, without throwing any exception.

Any help on understanding the cause of the freeze is welcome.

Thanks & Regards, Mattia!

Answer 1

Try to use the capture.read(frame); .