How to remove small connected objects using OpenCV

Question

I use OpenCV and Python and I want to remove the small connected object from my image.

I have the following binary image as input:

The image is the result of this code:

dilation = cv2.dilate(dst,kernel,iterations = 2)
erosion = cv2.erode(dilation,kernel,iterations = 3)

I want to remove the objects highlighted in red:

How can I achieve this using OpenCV?

Answer 1

In order to remove objects automatically you need to locate them in the image. From the image you provided I see nothing that distinguishes the 7 highlighted items from others. You have to tell your computer how to recognize objects you don't want. If they look the same, this is not possible.

If you have multiple images where the objects always look like that you could use template matching techniques.

Also the closing operation doesn't make much sense to me.

Answer 2

#For isolated or unconnected blobs: Try this (you can set noise_removal_threshold to whatever you like and make it relative to the largest contour for example or a nominal value like 100 or 25).

    mask = np.zeros_like(img)
    for contour in contours:
      area = cv2.contourArea(contour)
      if area > noise_removal_threshold:
        cv2.fillPoly(mask, [contour], 255)