为什么我的程序在视频的第一帧之后终止？

Question

我目前正在开发一个程序，该程序将来自网络摄像头的视频作为输入，然后检测该视频中的移动，在对象周围画线以显示它们移动的位置。

但是，当我运行这个程序时，它所做的一切都是从我的网络摄像头中显示一张静止图像。我很清楚为什么会发生这种情况 - if 语句 if (!(matFrame.empty())) 被评估为 false，因此 else 语句运行s，将 keepProcessing 更改为 false。然后终止 while 循环，只留下 ims.showImage(matFrame); 作为输出。

我不知道为什么会这样，所以我希望这里有人可以帮助我。我已经发布了下面的代码，因此您可以检查问题。我还尝试运行用视频对其进行调试，以确保这不是我的网络摄像头的问题，但我发现了同样的问题。感谢您的宝贵时间。

public class CaptureVideo {

public static void main(String[] args) throws InterruptedException {

    // load the Core OpenCV library by name

    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);

    // create video capture device object

    VideoCapture cap = new VideoCapture();

    // try to use the hardware device if present

    int CAM_TO_USE = 0;

    // create a new image object

    Mat matFrame = new Mat();

    Mat previousFrame = new Mat();

    Mat diffFrame = new Mat();

    // try to open first capture device (0)

    try {
        cap.open(CAM_TO_USE);
    } catch (Exception e1) {
        System.out.println("No webcam attached");

        // otherwise try opening a video file 

        try{
            cap.open("files/video.mp4");
        } catch (Exception e2) {
            System.out.println("No video file found");
        }
    }

    // if the a video capture source is now open

    if (cap.isOpened())
    {

        // create a new window object

        Imshow ims = new Imshow("From video source ... ");

        boolean keepProcessing = true;

           // add a flag to check whether the first frame has been read
           boolean firstFrame = true;

           while (keepProcessing)
            {   
                // save previous frame before getting next one, but
                // only do this if the first frame has passed
                if (!firstFrame)
                    previousFrame = matFrame.clone();

                // grab the next frame from video source
                cap.grab();

                // decode and return the grabbed video frame
                cap.retrieve(matFrame);

                // if the frame is valid (not end of video for example)
                if (!(matFrame.empty()))
                {

                    // if we are on the first frame, only show that and
                    // set the flag to false
                    if (firstFrame) {
                        ims.showImage(matFrame);
                        firstFrame = false;
                    }

                    // now show absolute difference after first frame
                    else {                
                        Core.absdiff(matFrame, previousFrame, diffFrame);
                        ims.showImage(diffFrame);                 
                    }

                    // now convert it to grey and threshold it

                    Mat grey = new Mat();
                    Imgproc.cvtColor(diffFrame, grey, Imgproc.COLOR_BGR2GRAY);

                    Imgproc.adaptiveThreshold(grey, diffFrame, 255, Imgproc.ADAPTIVE_THRESH_MEAN_C, 
                                                Imgproc.THRESH_BINARY_INV, 7, 10);

                    // now clean it up using some morphological operations

                    Size ksize = new Size(15,15);
                    Mat kernel =  Imgproc.getStructuringElement(Imgproc.MORPH_ELLIPSE, ksize);

                    Imgproc.morphologyEx(diffFrame, diffFrame, Imgproc.MORPH_CLOSE, kernel);

                    // find the all the contours from the binary image using the edge to contour
                    // stuff we looked at in lectures

                    List<MatOfPoint> contours = new Vector<MatOfPoint>();

                    Imgproc.findContours(diffFrame, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);

                    // draw the contours on image 2 in red

                    Imgproc.drawContours(matFrame, contours, -1, new Scalar(0,0,255));

                    // find the largest contour by area 

                    double maxArea = 0;
                    int maxAreaIndex = 0;

                    for (int i = 0; i < contours.size(); i++) {

                        double area = Imgproc.contourArea(contours.get(i), false);

                        if ( area > maxArea )
                        {
                            maxArea = area;
                            maxAreaIndex = i;
                        }
                    }

                    // draw the largest contour in red

                    Imgproc.drawContours(matFrame, contours, maxAreaIndex, new Scalar(0,255,0));

                    // create a new window objects

                    Imshow ims_diff = new Imshow("Difference");

                   // display images

                    ims_diff.showImage(diffFrame);

                    // display image with a delay of 40ms (i.e. 1000 ms / 25 = 25 fps)                
                    Thread.sleep(40);
                } else { 
                    keepProcessing = false;

                }
            }
      }
   }
}

Answer 1

您应该会在控制台或输出中看到异常 window:

OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cv::cvtColor, file ..\..\..\..\opencv\modules\imgproc\src\color.cpp, line 3739
Exception in thread "main" CvException [org.opencv.core.CvException: cv::Exception: ..\..\..\..\opencv\modules\imgproc\src\color.cpp:3739: error: (-215) scn == 3 || scn == 4 in function cv::cvtColor
]
    at org.opencv.imgproc.Imgproc.cvtColor_1(Native Method)
    at org.opencv.imgproc.Imgproc.cvtColor(Imgproc.java:4598)
    at CaptureVideo.main(CaptureVideo.java:87)

第 87 行（在我的源文件中）是：

Imgproc.cvtColor(diffFrame, grey, Imgproc.COLOR_BGR2GRAY);

问题是 diffFrame 还没有初始化，所以它被炸毁了。通过添加这个块，我能够让它在本地工作：

// decode and return the grabbed video frame
cap.retrieve(matFrame);

// *** START
if (firstFrame) {
    firstFrame = false;
    continue;
}
// *** End

// if the frame is valid (not end of video for example)
if (!(matFrame.empty()))

这样做的效果是第一帧不画，后面的画。此外，稍后的代码将为每个 "diff" 帧打开一个新的 JFrame (Imshow)，这将很快杀死你的机器，所以准备好杀死进程。

为什么我的程序在视频的第一帧之后终止？

Why does my program terminate after the first frame of the video?

java

opencv

image-processing