I can find the circle when I look for the Hoff circle on a grayscale image through opencv, but once I binarize that grayscale image through OpenCV, I can"t find the circle. Here"s some code

 Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image_test);
        Mat srcMat=new Mat();
        Utils.bitmapToMat(bitmap,srcMat);
        Mat grayMat=new Mat();
        //
        Imgproc.cvtColor(srcMat,grayMat,Imgproc.COLOR_RGB2GRAY);
        Mat binaryMat =new Mat();
        //
        Imgproc.threshold(grayMat,binaryMat,40,255,Imgproc.THRESH_BINARY);
          // grayMat  binaryMat
        Mat effectMat = OpenCvHelper.findEffectArea(grayMat, 5, 20, 5,
                seekbarWidth.getProgress(),
                seekbarHeight.getProgress(),
                seekbarIntervalx.getProgress(),
                seekbarIntervaly.getProgress());
        if (effectMat == null) {
            Toast.makeText(this, "", Toast.LENGTH_SHORT).show();
            return;
        }
        mImage.setImageBitmap(mat2Bitmap(effectMat));

here is the code to find the circle in OpencvHelper.findEffectArea ():

        Mat matchAnchorMat = new Mat();
         Imgproc.HoughCircles(mat, matchAnchorMat, Imgproc.CV_HOUGH_GRADIENT, 1, minDist, param1, param2, minRadius, maxRadius);
        int size = matchAnchorMat.cols();
        Log.w(TAG,"findCircle() :"+size);
        List<CircleInfo> pointList = new ArrayList<>();
        for (int i = 0; i < size; iPP) {
            double[] data = matchAnchorMat.get(0, i);
            CircleInfo circleInfo = new CircleInfo(data[0], data[1], data[2]);
            pointList.add(circleInfo);
        }
        return pointList;