Finding coordinates of each pixel using programming

Question

What is the way to find the coordinates of each pixel of the inner circle (or the outer one) in the following Image using programming(openCV or MATLAB)?
imtool gives this information but it is mouse driven.

Update

I used imtool to detect these locations, by putting my mouse cursor on each point on the circle and manual noting this value. But how do I do it using programming as manually I cant do it for so many pints on the circle.

Answer 1

In Matlab, you can just do:

im = imread('im.png');      %# load image
[y,x] = find(all(im<5, 3)); %# find black pixels
position = [x,y];           %# display them