idamnjanovic@60: function f = pwsmoothfield(n,var,alpha)
idamnjanovic@60: % PWSMOOTHFIELD(N,VAR,ALPHA)
idamnjanovic@60: %   Generate an image of piecewise smooth filtered white noise
idamnjanovic@60: %
idamnjanovic@60: %   N = sidelength of the field in pixels
idamnjanovic@60: %   VAR = variance of original white nose
idamnjanovic@60: %   ALPHA = fraction of FFT coefficents to keep
idamnjanovic@60: %
idamnjanovic@60: %   Returns an N-by-N array
idamnjanovic@60: %
idamnjanovic@60: %   This file is used with the kind permission of Stephen J. Wright
idamnjanovic@60: %   (swright@cs.wisc.edu), and was originally included in the GPSR
idamnjanovic@60: %   v1.0 distribution: http://www.lx.it.pt/~mtf/GPSR .
idamnjanovic@60: 
idamnjanovic@60: % $Id: pwsmoothfield.m 1040 2008-06-26 20:29:02Z ewout78 $
idamnjanovic@60: 
idamnjanovic@60: f = sqrt(var)*randn(n);
idamnjanovic@60: F = fft2(f);
idamnjanovic@60: a = ceil(n*alpha/2);
idamnjanovic@60: b = fix(n*(1-alpha));
idamnjanovic@60: F(a+1:a+b,:) = 0;
idamnjanovic@60: F(:,a+1:a+b) = 0;
idamnjanovic@60: f = real(ifft2(F));
idamnjanovic@60: 
idamnjanovic@60: for i = 1:n
idamnjanovic@60:     for j = 1:n
idamnjanovic@60:         if (j/n >= 15*(i/n - 0.5)^3 + 0.4)
idamnjanovic@60:             f(i,j) = f(i,j) + sqrt(var);
idamnjanovic@60:         end
idamnjanovic@60:     end
idamnjanovic@60: end
idamnjanovic@60: