thin the boundary of objects of black & white images

I have a black and white image consists of very simple geometric shapes. the boundaries of the shapes are very thick. i want to thin them and skel. how can i do it?

Answer 1

[David Sanchez]

Use imerode.

From Matlab documentation:

IM2 = imerode(IM,SE) erodes the grayscale, binary, or packed binary image IM, returning the eroded image IM2. The argument SE is a structuring element object or array of structuring element objects returned by the strel function.

Example:

Erode a binary image with a disk structuring element.

originalBW = imread('circles.png');  
se = strel('disk',11);        
erodedBW = imerode(originalBW,se);
imshow(originalBW), figure, imshow(erodedBW)