如何在Android中使用Opencv有效地对图像进行Canny边缘检测?

我正在制作一个Android应用程序来检测图像中的多个对象,然后处理这些对象并将它们与参考对象进行比较,以检测异常。我用python测试了不同的图像边缘检测器,Prewitt操作符给出了最好的结果,如下所示 https://i.imgur.com/4iwOx9s.png 对于android,我使用了Canny edge detector,但结果不如Prewitt,如下所示 https://i.imgur.com/Bax1Wxw.png

这是我试过的java代码

    Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.coffret);

    //compress bitmap
    bmp = getResizedBitmap(bmp, 500);

    Mat rgbMat = new Mat();
    Utils.bitmapToMat(bmp, rgbMat);


    Mat grayMat = new Mat();
    Mat bwMat = new Mat();

    Imgproc.cvtColor(rgbMat, grayMat, Imgproc.COLOR_RGB2GRAY);
    Imgproc.equalizeHist(grayMat, grayMat);

    //Imgproc.adaptiveThreshold(grayMat, grayMat, 255, Imgproc.ADAPTIVE_THRESH_MEAN_C, Imgproc.THRESH_BINARY, 15, 40);
    Imgproc.Canny(grayMat, bwMat, 50, 200, 3, false);

    //find largest contour
    List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
        Imgproc.findContours(bwMat, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_NONE);

        double maxArea = -1;
        int maxAreaIdx = -1;
        if (contours.size() > 0) {
            MatOfPoint temp_contour = contours.get(0); //the largest is at the index 0 for starting point
            MatOfPoint2f approxCurve = new MatOfPoint2f();
            Mat largest_contour = contours.get(0);
            List<MatOfPoint> largest_contours = new ArrayList<MatOfPoint>();
            for (int idx = 0; idx < contours.size(); idx++) {
                temp_contour = contours.get(idx);
                double contourarea = Imgproc.contourArea(temp_contour);
                //compare this contour to the previous largest contour found
                if (contourarea > maxArea) {
                    //check if this contour is a square
                    MatOfPoint2f new_mat = new MatOfPoint2f( temp_contour.toArray() );
                    int contourSize = (int)temp_contour.total();
                    Imgproc.approxPolyDP(new_mat, approxCurve, contourSize*0.05, true);
                    if (approxCurve.total() == 4) {
                        maxArea = contourarea;
                        maxAreaIdx = idx;
                        largest_contours.add(temp_contour);
                        largest_contour = temp_contour;
                    }
                }
            }

            if (largest_contours.size() >= 1) {
                MatOfPoint temp_largest = largest_contours.get(largest_contours.size()-1);
                largest_contours = new ArrayList<MatOfPoint>();
                largest_contours.add(temp_largest);
                Imgproc.cvtColor(bwMat, bwMat, Imgproc.COLOR_BayerBG2RGB);
                Imgproc.drawContours(bwMat, largest_contours, -1, new Scalar(0, 255, 0), 1);
            }
        }


    Utils.matToBitmap(bwMat, bmp);

    Matrix matrix = new Matrix();
    matrix.postRotate(180);

    bmp = Bitmap.createBitmap(bmp, 0, 0, bmp.getWidth(), bmp.getHeight(), matrix, true);

    imgView.setImageBitmap(bmp);

如您所注意到的,使用Prewitt操作符,文本更清晰,轮廓更清晰。 我认为我没有正确地应用Canny,这就是为什么没有检测到最大轮廓。我做错什么了?

编辑: 这是原图 https://i.imgur.com/BtyZOvj.jpg