How to exactly count the number of lines in a image using opencv

Question

How to count exactly the lines between the numbers, total count must be 6.

I'm using this method to count the number of lines using openCV and I got the grayscale image.

Is lines.cols() the right way to count the number of lines in an image?

public String Func() {

    Bitmap bitmap = BitmapFactory.decodeResource(getApplicationContext().getResources(), R.drawable.park);
    mat = new Mat();
    edges = new Mat();
    Mat mRgba = new Mat(612, 816, CvType.CV_8UC1);
    Mat lines = new Mat();


    Utils.bitmapToMat(bitmap, mat);
    Imgproc.Canny(mat, edges, 50, 90);

    int threshold = 50;
    int minLineSize = 20;
    int lineGap = 20;

    Imgproc.HoughLinesP(edges, lines, 1, Math.PI / 180, threshold, minLineSize, lineGap);


    int count = lines.cols();
    System.out.println("count = " + count);
    String cou = String.valueOf(count);

    for (int x = 0; x < lines.cols(); x++) {
        double[] vec = lines.get(0, x);
        double x1 = vec[0],
                y1 = vec[1],
                x2 = vec[2],
                y2 = vec[3];

        Point start = new Point(x1, y1);
        Point end = new Point(x2, y2);
        Core.line(mRgba, start, end, new Scalar(255, 0, 0), 3);

    }

    Bitmap bmp = Bitmap.createBitmap(mRgba.cols(), mRgba.rows(), Bitmap.Config.ARGB_8888);
    Utils.matToBitmap(mRgba, bmp);
    bitmap = bmp;

    Drawable d = new BitmapDrawable(Resources.getSystem(), bitmap);
    img2.setImageDrawable(d);

    return cou;
}

score 0 · Answer 1 · edited May 23 '17 at 10:31

0

According to this SO's answer and this one, your code sample seems correct.

To get better results, prior to applying canny filter, you should do a color threshold on the image to only keep the white painted strips.

Other than that, I think you should increase your minLineSize in order to discard too short lines.

edited May 23 '17 at 10:31

Community

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answered May 11 '17 at 08:13

Elouarn Laine

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I have the opencv sdk of lower version.Im getting error in the first line,can u provide me the link to download new version of opencv sdk – San May 11 '17 at 08:43
@San What OpenCV's version do you have? I've updated my post with a 2nd method, can you give it a try? – Elouarn Laine May 11 '17 at 08:51
I have version 2.3 now Im downloading 3.2. and one more thing Im using opencv in android..ur code looks like c++ – San May 11 '17 at 09:22
that was not helpful – San May 11 '17 at 10:21
@San Do you mind explaining what your problem is? Any errors? – Elouarn Laine May 11 '17 at 10:32
@San Can you print `lines.rows()` and `lines.cols()` and tell me the result? – Elouarn Laine May 11 '17 at 12:37
ya I did lines.cols() is 64 and lines.rows() is 3. lines.cols() considers everying as a line – San May 11 '17 at 12:47
@San Are you running OpenCV 3.2 now? Can you try to print x1, y1, x2, y2 for the first columns of the lines mat? – Elouarn Laine May 11 '17 at 13:32
when i run the above code I could not get even the greyscale image – San May 12 '17 at 06:15
@San, `Canny` needs a greyscale image, but in your code I don't see any color conversions, add this line before `Canny` : `Imgproc.cvtColor(mat, mat, Imgproc.COLOR_BGR2GRAY);` As far as I understand, your code should display an image with blue lines on a black background, is it the case? – Elouarn Laine May 12 '17 at 07:43

How to exactly count the number of lines in a image using opencv

1 Answers1