How to generate a circular mask ?

How to generate a image mask (500X500) having circles at specified centre points.I have with me the centre(different) and radius(same) of the circles with me. How to create a mask having circles generated at those centre points with the radius that is same.

Answer 1

[Walter Roberson]

http://www.mathworks.com/matlabcentral/newsreader/view_thread/291115

http://www.mathworks.com/matlabcentral/fileexchange/47905-createcirclesmask-m