The is_contour_bad function requires a single argument, c, which is the contour we are going to test to determine if it should be removed or not. This function handles the implementation of Step 3 above and defines the criterion under which a contour should be marked as “bad” and removed from an image. We then define our is_contour_bad function on Line 6. We’ll use NumPy for numerical processing and cv2 for our OpenCV bindings. The first thing we’ll do is import our necessary packages.

# the contour is 'bad' if it is not a rectangle Open up a new file, name it remove_contours.py, and let’s get coding: # import the necessary packagesĪpprox = cv2.approxPolyDP(c, 0.02 * peri, True) We’ll accomplish this by applying a test to every contour to determine if it should be removed or not.Īnyway, let’s go ahead and get this example started. In this toy example our goal is to remove the circles/ellipses from the image above while retaining the rectangles.

Our goal is to remove all circles/ellipses while retaining the rectangles. Removing contours from an image using Python and OpenCV Figure 1: Our example toy image. This example will run on Python 2.7/Python 3.4+ and OpenCV 2.4.X. Looking for the source code to this post? Jump Right To The Downloads Section From here, you’ll be able to take this code and modify the contour removal criterion according to your own needs. And while it’s impossible for me to guess the criterion as to why you want to remove a contoured region from an image, the remainder of this blog post will demonstrate a toy example that you can use to remove contours from an image. This step could be very simple - or it also could be quite hard, it really depends on your application. The algorithm itself is very straightforward, the main step that you need to pay attention to and consider is Step 3, determining if a contour should be removed.

Step 5: Apply the accumulated mask of bad contours to the original image using a bitwise ‘and’.

Step 4: Accumulate a mask of “bad” contours to be removed.

Step 3: Determine if the contour is “bad” and should be removed according to some criterion.

Step 2: Loop over contours individually.

Step 1: Detect and find contours in your image.

The basic algorithm for removing contours from an image goes something like this: Click here to download the source code to this postĪwhile back I was going through /r/computervision when I stumbled across a question asking how to remove contours from an image using OpenCV.

Flexistarter remove contour line