Extending a contour in OpenCv

4
votes

i have several contours that consist of several black regions in my image. Directly adjacent to these black regions are some brighter regions that do not belong to my contours. I want to add these brighter regions to my black region and therefor extend my contour in OpenCv.
Is there a convenient way to extend a contour? I thought about looking at intensity change from my gradient-image created with cv::Sobel and extend until the gradient changes again, meaning the intensity of pixel is going back to the neither black nor bright regions of the image.

Thanks!

Here are example images. The first picture shows the raw Image, the second the extracted Contour using Canny & findContours, the last one the Sobel-Gradient intensity Image of the same area. I want to include the bright boundaries in the first image to the Contour.

enter image description hereenter image description hereenter image description here

Update: Now i've used some morphological operations on the Sobelgradients and added a contour around them (see Image below). Next step could be to find the adjacent pair of purple & red contours, but it seems very much like a waste of procession time to actually have to search for directly adjacent contours. Any better ideas?

enter image description here

Update 2: My solution for now is to search for morphed gradient (red) contours in a bounding box around my (purple) contours and pick the one with correct orientation & size. This works for gradient contours where the morphological operation closes the "rise" and "fall" gradient areas like in Figure 3. But it is still a bad solution for cases in which the lighted area is wider then in the image above. Any idea is still very much appreciated, thanks!

1
c++image-processingopencv
Please provide a sample image !!! - Abid Rahman K
Okay, added some pictures and clarification to my question. - moatilliatta

1 Answers

3
votes

What you're trying to do is find two different features and merge them. It's not terribly difficult but you have to use multiple copies of the image to make it happen.

  1. Make one copy, and threshold it for the dark portion
  2. Make another copy and threshold it for the light portion
  3. Merge both thresholded images into a new image
  4. Apply a morphological operation like opening or closing (depending on how you threshold) This will connect nearby components
  5. Find contours in the resultant image
  6. Use those contours on your original image. This will work since all the images are the same size and all based off of the original.