OpenCV android : Hough transform rectangle recognition with image with multiple different sized rectangles

Question

So everyone, my first question on stackoverflow. I have been working with android and openCV for a month and I was able to successfully implement template Matching. Now, the next task is to detect all the rectangles in the image and get the coordinates (I actually want the color of every rectangle) for research purposes. Kindly help. I tried using Hough transform with canny edge detection but unfortunately it doesn't detect the small rectangles which is the primary concern now.

Thank you!![![Have to detect all the rectangles, small and big ones

Answer 1

So I'm really proud to post an answer to my own question. Hope this helps someone in future. There are obviously a lot of ways to do this but the most accurate way was to use template matching on the main image to find the coordinates of the biggest rectangle and since all the other rectangles are equidistant to the corner points, center of every rectangle can be found which gives the desired colors.

The thin strip in the middle was also recognized by template matching and then a gradient operator represented the various rectangles, every peak in the gradient represents the rectangles.

Kindly comment for code. For research purposes I cannot post to anonymous.