Android opencv(四)轮廓检测

轮廓检测函数：
Imgproc. findContours(image, contours, hierarchy, mode, method)
通过轮廓检测找到面积最大的轮廓并绘制轮廓：

        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);        //绘制检测到的轮廓         Imgproc.drawContours(mRgba, contours, maxAreaIdx, new Scalar(0,255,0), 5);

//通过轮廓检测获取4个交点

    public static List<Point> getCornersByContour(Mat imgsource){        List<MatOfPoint> contours=new ArrayList<>();        //轮廓检测        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);//假设最大的轮廓在index=0处        MatOfPoint2f approxCurve=new MatOfPoint2f();        for (int idx=0;idx<contours.size();idx++){            temp_contour=contours.get(idx);            double contourarea=Imgproc.contourArea(temp_contour);            //当前轮廓面积比最大的区域面积大就检测是否为四边形            if (contourarea>maxArea){                //检测contour是否是四边形                MatOfPoint2f new_mat=new MatOfPoint2f(temp_contour.toArray());                int contourSize= (int) temp_contour.total();                MatOfPoint2f approxCurve_temp=new MatOfPoint2f();                //对图像轮廓点进行多边形拟合                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);        //对4个点进行排序        Point centerPoint=new Point(0,0);//质心        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;    }