how can i rounding corners in circle

Hello all

I have an image which has edge information. i will round the pixels value to fixed it for my real project. but they lost their form. i want to give they new form like at start. i'll explain what is real problem

I take a picture and do edges detection with canny filter. This image has a letter 'B' and 'O'. i get the edges and i divide and round my pixels value to my real work, too much. and i need smaller value to this. in here, my image has edge with corners like stair-edge. 'B's and 'O's round parts become like sawtooth. i want to change this edges to circle with any function. in att. i share with you what i have, and what i want.

sorry for bad english, thanks in advance.