OpenCV on Android findContours throws Exception

Question

I use OpenCV 2.4.0 on Android and try to find contours in a binary imgage.

List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Mat mIntermediateMat = new Mat();
Imgproc.Canny(img, mIntermediateMat, 50, 100);
Imgproc.findContours(mIntermediateMat, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);

But the function throws a "Unrecognized or unsupported array type in function CvMat..." exception.

Also i try this Mat as input:

Mat mIntermediateMat = new Mat(height, width, CvType.CV_8UC1, new Scalar(0));

But i get the same exception.

I think i found the problem. The size of the input Mat ist to large. — ChHaupt
– ChHaupt, Commented Sep 20, 2012 at 15:08

Joker · Accepted Answer · 2014-09-15 02:30:30Z

Try this function to find contours :

public static ArrayList<Rect> detection_contours(Mat outmat) {
    Mat v = new Mat();
    Mat vv = outmat.clone();
    List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
    Imgproc.findContours(vv, contours, v, Imgproc.RETR_LIST,
            Imgproc.CHAIN_APPROX_SIMPLE);

    double maxArea = 100;
    int maxAreaIdx = -1;
    Rect r = null;
    ArrayList<Rect> rect_array = new ArrayList<Rect>();

    for (int idx = 0; idx < contours.size(); idx++) {
        Mat contour = contours.get(idx);
        double contourarea = Imgproc.contourArea(contour);
        if (contourarea > maxArea) {
            // maxArea = contourarea;
            maxAreaIdx = idx;
            r = Imgproc.boundingRect(contours.get(maxAreaIdx));
            rect_array.add(r);
          //  Imgproc.drawContours(imag, contours, maxAreaIdx, new Scalar(0,0, 255));
        }

    }

    v.release();

    return rect_array;

}

Rui Marques · Accepted Answer · 2012-09-18 11:00:10Z

0

Make sure that after the Canny() call, your mIntermediateMat is of type CvType.CV_8*

answered Sep 18, 2012 at 11:00

Rui Marques

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3 Comments

ChHaupt Over a year ago

But the Mat mIntermediateMat = new Mat(height, width, CvType.CV_8UC1, new Scalar(0)); should work?

Rui Marques Over a year ago

It should if it is after canny. Please post the complete error message if you still have problems.

ChHaupt Over a year ago

After the Canny the image type is CV_8UC1. And Mat mIntermediateMat = new Mat(height, width, CvType.CV_8UC1, new Scalar(0)); replaced the canny. The complete error message is: "CvException [org.opencv.core.CvException: ../modules/core/src/array.cpp:2482: error: (-206) Unrecognized or unsupported array type in function CvMat* cvGetMat(const CvArr*, CvMat*, int*, int)"

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