輪廓檢測函式：
Imgproc. findContours(image, contours, hierarchy, mode, method)
通過輪廓檢測找到面積最大的輪廓並繪製輪廓：

        List<MatOfPoint> contours=new ArrayList<>();
        Imgproc.findContours(blurredImage,contours,new Mat(),Imgproc.RETR_LIST,Imgproc.CHAIN_APPROX_SIMPLE);
        double maxVal = 0;
        int
 
 maxValIdx = 0;
        for (int contourIdx = 0; contourIdx < contours.size(); contourIdx++)
        {
            double contourArea = Imgproc.contourArea(contours.get(contourIdx));
            if (maxVal < contourArea)
            {
                maxVal = contourArea;
                maxValIdx = contourIdx;
            }
        }
 Mat mRgba=new
 
 Mat();
        mRgba.create(blurredImage.rows(), blurredImage.cols(), CvType.CV_8UC3);
        //繪製檢測到的輪廓
         Imgproc.drawContours(mRgba, contours, maxAreaIdx, new Scalar(0,255,0), 5);

//通過輪廓檢測獲取4個交點

    public static List<Point> getCornersByContour(Mat imgsource){
        List<MatOfPoint> contours=new
 
 ArrayList<>();
        //輪廓檢測
        Imgproc.findContours(imgsource,contours,new Mat(),Imgproc.RETR_LIST,Imgproc.CHAIN_APPROX_SIMPLE);
        double maxArea=-1;
        int maxAreaIdx=-1;
        MatOfPoint temp_contour=contours.get(0);//假設最大的輪廓在index=0處
        MatOfPoint2f approxCurve=new MatOfPoint2f();
        for (int idx=0;idx<contours.size();idx++){
            temp_contour=contours.get(idx);
            double contourarea=Imgproc.contourArea(temp_contour);
            //當前輪廓面積比最大的區域面積大就檢測是否為四邊形
            if (contourarea>maxArea){
                //檢測contour是否是四邊形
                MatOfPoint2f new_mat=new MatOfPoint2f(temp_contour.toArray());
                int contourSize= (int) temp_contour.total();
                MatOfPoint2f approxCurve_temp=new MatOfPoint2f();
                //對影象輪廓點進行多邊形擬合
                Imgproc.approxPolyDP(new_mat,approxCurve_temp,contourSize*0.05,true);
                if (approxCurve_temp.total()==4){
                    maxArea=contourarea;
                    maxAreaIdx=idx;
                    approxCurve=approxCurve_temp;
                }
            }
        }
        double[] temp_double=approxCurve.get(0,0);
        Point point1=new Point(temp_double[0],temp_double[1]);

        temp_double=approxCurve.get(1,0);
        Point point2=new Point(temp_double[0],temp_double[1]);

        temp_double=approxCurve.get(2,0);
        Point point3=new Point(temp_double[0],temp_double[1]);
        temp_double=approxCurve.get(3,0);

        Point point4=new Point(temp_double[0],temp_double[1]);

        List<Point> source=new ArrayList<>();
        source.add(point1);
        source.add(point2);
        source.add(point3);
        source.add(point4);
        //對4個點進行排序
        Point centerPoint=new Point(0,0);//質心
        for (Point corner:source){
            centerPoint.x+=corner.x;
            centerPoint.y+=corner.y;
        }
        centerPoint.x=centerPoint.x/source.size();
        centerPoint.y=centerPoint.y/source.size();
        Point lefttop=new Point();
        Point righttop=new Point();
        Point leftbottom=new Point();
        Point rightbottom=new Point();
        for (int i=0;i<source.size();i++){
            if (source.get(i).x<centerPoint.x&&source.get(i).y<centerPoint.y){
                lefttop=source.get(i);
            }else if (source.get(i).x>centerPoint.x&&source.get(i).y<centerPoint.y){
                righttop=source.get(i);
            }else if (source.get(i).x<centerPoint.x&& source.get(i).y>centerPoint.y){
                leftbottom=source.get(i);
            }else if (source.get(i).x>centerPoint.x&&source.get(i).y>centerPoint.y){
                rightbottom=source.get(i);
            }
        }
        source.clear();
        source.add(lefttop);
        source.add(righttop);
        source.add(leftbottom);
        source.add(rightbottom);
        return source;
    }

ps：輪廓檢測的輸入影象必須是二值化的圖片否則只能檢測一個輪廓。