MATLAB: How to detect orientation of an object

Question

Hello!

I've been stuck on this particular task for a while, so I thought I would ask the Computer Vision gurus on here. So far I've tried regionprops (specifically – orientation property of regionprops), which has been fairly poor for in terms of results. I was wondering if anyone has any tips or method for which I could calculate the orientation of a letter in the attached image. I've also attached an example image of what I would like to achieve.

Thank you.

Edit: Attached an input example image

Edit2: Attached imgmat.mat file containing the original image and a binary image.

Edit3: Attached shapeLetters.mat binary and an RGB image containing both letters and shapes for possible advice on clean segmentation of shapes and letters.

Answer 1

First find the letters. Pretty easy. Just threshold and call imclearborder() to get rid of the background, then do a little cleanup with bwareafilt() or bwareaopen().

Then detect which letter is which with Hu's moments http://www.youtube.com/watch?v=Nc06tlZAv_Q or Deep Learning. Or else just get the orientation from regionprops() and look at the angle delta from a correctly oriented letter.