ivan@77: function f = pwsmoothfield(n,var,alpha)
ivan@77: % PWSMOOTHFIELD(N,VAR,ALPHA)
ivan@77: %   Generate an image of piecewise smooth filtered white noise
ivan@77: %
ivan@77: %   N = sidelength of the field in pixels
ivan@77: %   VAR = variance of original white nose
ivan@77: %   ALPHA = fraction of FFT coefficents to keep
ivan@77: %
ivan@77: %   Returns an N-by-N array
ivan@77: %
ivan@77: %   This file is used with the kind permission of Stephen J. Wright
ivan@77: %   (swright@cs.wisc.edu), and was originally included in the GPSR
ivan@77: %   v1.0 distribution: http://www.lx.it.pt/~mtf/GPSR .
ivan@77: 
ivan@77: % $Id: pwsmoothfield.m 1040 2008-06-26 20:29:02Z ewout78 $
ivan@77: 
ivan@77: f = sqrt(var)*randn(n);
ivan@77: F = fft2(f);
ivan@77: a = ceil(n*alpha/2);
ivan@77: b = fix(n*(1-alpha));
ivan@77: F(a+1:a+b,:) = 0;
ivan@77: F(:,a+1:a+b) = 0;
ivan@77: f = real(ifft2(F));
ivan@77: 
ivan@77: for i = 1:n
ivan@77:     for j = 1:n
ivan@77:         if (j/n >= 15*(i/n - 0.5)^3 + 0.4)
ivan@77:             f(i,j) = f(i,j) + sqrt(var);
ivan@77:         end
ivan@77:     end
ivan@77: end
ivan@77: