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find contours miss some objects

asked 2017-06-28 04:40:20 -0600

Nani gravatar image

updated 2017-08-02 11:50:05 -0600

I use the following code to read through all objects that I segmented from my image which should be ordered in row and columns as semi-circle (because of segmentation and morphological processing for reducing noise):

    Imgproc.Canny(srcImg, srcImg, 50, 150);
    Imgcodecs.imwrite("/mnt/sdcard/DCIM/cannyImg.jpg", srcImg);//check

    List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
    Mat hierarchy = new Mat();
    Imgproc.findContours(srcImg, contours, hierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE, new Point(0,0));

    //int index = 0;
    //double maximc = Imgproc.contourArea(contours.get(0));
    for (int contourIdx = 1; contourIdx < contours.size(); contourIdx++) {
        double temp;
        temp = Imgproc.contourArea(contours.get(contourIdx));
        if (temp > 100) { 
                           // condition to differentiate between noise and objects
            Mat drawing = Mat.zeros(srcImg.size(), CvType.CV_8UC1);
            Imgproc.drawContours(drawing, contours, contourIdx, new Scalar(255), -1);

            Mat resultMat = new Mat();
            maskImg.copyTo(resultMat, drawing);
            Imgcodecs.imwrite("/mnt/sdcard/DCIM/resultImg" + contourIdx + ".jpg", resultMat);//check

however, the loop can not read important objects in my image even canny image is correct and can identify all the objects. My questions are: in which order find contours read objects? and also is there another way in Opencv to read through all objects in the image other than find contours? last question i used the size of contours to differentiate between the objects and the noise, so is this Ok or you can suggest other methods.

Attached is the result image and the one with red circles correctly identified while the others which I need not being identified.

Any help is appreciated

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int contourIdx = 0; (you're already missing the 1st object here)

if (temp > 100) (maybe you need a better "filter" ?)

berak gravatar imageberak ( 2017-06-29 01:48:30 -0600 )edit

I changed the contourIdx to start at 0 and the problem is still on. I thought it may be due to objects become open (not closed objects) after morphological processing; Is that could be the reason?

Nani gravatar imageNani ( 2017-06-29 03:19:47 -0600 )edit

sounds likely. but can you try to add the canny image, and somehow highlight, where it goes wrong ?

(reduce the speculation )

berak gravatar imageberak ( 2017-06-29 03:29:54 -0600 )edit

@berak how to add image in here

Nani gravatar imageNani ( 2017-06-29 04:23:15 -0600 )edit

edit your question, it has an image button.

or use markup : ![description](img_url)

berak gravatar imageberak ( 2017-06-29 04:27:33 -0600 )edit

Thanks @berak I added the result image.

Nani gravatar imageNani ( 2017-06-29 05:03:39 -0600 )edit

@berak, do you know how I can find the objects myself by using the findnonezero() or countnonezero() functions to read all the objects and how to calculate the black distance between white objects.

Please help.

Nani gravatar imageNani ( 2017-07-12 08:54:54 -0600 )edit

If I change the retrieval mode to RETR_LIST or RETR_CCOMP, I can get all the objects but with redundancy then how to get rid of redundant objects is my question.

Nani gravatar imageNani ( 2017-07-12 10:05:51 -0600 )edit

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answered 2017-07-13 09:04:50 -0600

Nani gravatar image

I threshold the image for other processing before finding contours then I applied Canny and this causes my problem and after removing canny and use RETR_CCOMP mode which gives 2 level of hierarchy, I can now get the correct result.

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Asked: 2017-06-28 04:40:20 -0600

Seen: 208 times

Last updated: Aug 02 '17