function a = putbad(a,x,y,r) % Put a 'bad' cell in image a [m,n] = size(a); % This code is not optimized for speed [mm,nn] = meshgrid(1:m,1:n); d2 = (mm - x).^2 + (nn - y).^2; a(find((mm - y).^2 + (nn - x).^2 <= r^2)) = 0.5; a(find((mm - y).^2 + (nn - x).^2 <= (r/2)^2)) = 1;