如何去除重叠的轮廓

Question

我正在开发一个程序，试图从拼图中提取彩色方块。我从视频捕获中获取一帧，然后找到所有轮廓。然后我删除不是正方形的轮廓（这工作正常但正在寻找更好的方法）。我面临的主要问题是轮廓重叠。我使用 RETR_TREE 获取所有轮廓，但是当使用 RETR_EXTERNAL 时，轮廓变得更难检测。有什么方法可以改进正方形的检测吗？或者我可以删除图像中重叠轮廓的方法。

这是一张轮廓重叠的图像：在这张图片中找到了 11 个轮廓，但我只想要 9 个。（我画了矩形以更容易地看到重叠部分）

。如何去除内部轮廓？这是我的代码：

public Mat captureFrame(Mat capturedFrame){

    Mat newFrame = new Mat();
    capturedFrame.copyTo(newFrame); 

    //Gray
    Mat gray = new Mat();
    Imgproc.cvtColor(capturedFrame, gray, Imgproc.COLOR_RGB2GRAY);

    //Blur
    Mat blur = new Mat();
    Imgproc.blur(gray, blur, new Size(3,3));
    //Canny image
    Mat canny = new Mat();
    Imgproc.Canny(blur, canny, 20, 40, 3, true);

    //Dilate image to increase size of lines
    Mat kernel = Imgproc.getStructuringElement(1, new Size(3,3));
    Mat dilated = new Mat();
    Imgproc.dilate(canny,dilated, kernel);


    List<MatOfPoint> contours = new ArrayList<>();
    List<MatOfPoint> squareContours = new ArrayList<>();

    //find contours
    Imgproc.findContours(dilated, contours, new Mat(), Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_NONE);


    //Remove contours that aren't close to a square shape.
    //Wondering if there is a way I can improve this?
    for(int i = 0; i < contours.size(); i++){

        double area = Imgproc.contourArea( contours.get(i)); 
        MatOfPoint2f contour2f = new MatOfPoint2f(contours.get(i).toArray());

        double perimeter = Imgproc.arcLength(contour2f, true);
        //Found squareness equation on wiki... 
        //https://en.wikipedia.org/wiki/Shape_factor_(image_analysis_and_microscopy)
        double squareness = 4 * Math.PI * area / Math.pow(perimeter, 2);

        //add contour to new List if it has a square shape.
        if(squareness >= 0.7 && squareness <= 0.9 && area >= 3000){
           squareContours.add(contours.get(i));
        }
    }

    MatOfPoint2f approxCurve = new MatOfPoint2f();
    for(int n = 0; n < squareContours.size(); n++){

        //Convert contours(n) from MatOfPoint to MatOfPoint2f
        MatOfPoint2f contour2f = new MatOfPoint2f( squareContours.get(n).toArray());
        //Processing on mMOP2f1 which is in type MatOfPoint2f
        double approxDistance = Imgproc.arcLength(contour2f, true)*0.02;
        Imgproc.approxPolyDP(contour2f, approxCurve, approxDistance, true);

        //Convert back to MatOfPoint
        MatOfPoint points = new MatOfPoint( approxCurve.toArray());

        // Get bounding rect of contour
        Rect rect = Imgproc.boundingRect(points);
        //length and width should be about the same
        if(rect.height - rect.width < Math.abs(10)){
            System.out.printf("%s , %s \n", rect.height, rect.width);
        }

         // draw enclosing rectangle (all same color, but you could use variable i to make them unique)
        Imgproc.rectangle(newFrame, new Point(rect.x,rect.y), new Point(rect.x+rect.width,rect.y+rect.height),new Scalar (255, 0, 0, 255), 3); 

        }  

    return newFrame;
}

Answer 1

幸运的是，cv::findContours 还为我们提供了层次结构矩阵，您在代码段中忽略了它，层次结构对于 RETR_EXTERNAL 以外的所有模式都非常有用，您可以找到详细文档层次矩阵 here。

层次矩阵包含每个轮廓的 [下一个，上一个，First_Child，父] 格式的数据。现在你可以过滤轮廓，其逻辑如select only those contours where parent == -1，这将消除父轮廓内的子轮廓。

要使用层级矩阵，您需要将 cv::findContours 调用为：

cv::Mat hierarchy;
Imgproc.findContours(dilated, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_NONE);

如何去除重叠的轮廓

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