%  STEP2LINE - Generate test image interpolating a step to a line.%%  Function to generate a test image where the feature type changes%  from a step edge to a line feature from top to bottom%%  Usage:%      im = step2line(nscales, ampexponent, sze)%%      nscales     - No of fourier components used to construct the signal%      ampexponent - decay exponent of amplitude with frequency%                    a value of -1 will produce amplitude inversely%                    proportional to frequency (corresponds to step feature)%                    a value of -2 will result in the line feature%                    appearing as a triangular waveform.%      sze         - Optional size of image, defaults to 256x256%%      Returns:%              im  - Image showing the grating pattern%%  suggested parameters: %      step2line(100, -1) %% Copyright (c) 1997 Peter Kovesi% School of Computer Science & Software Engineering% The University of Western Australia% http://www.csse.uwa.edu.au/% % Permission is hereby granted, free of charge, to any person obtaining a copy% of this software and associated documentation files (the "Software"), to deal% in the Software without restriction, subject to the following conditions:% % The above copyright notice and this permission notice shall be included in % all copies or substantial portions of the Software.%% The Software is provided "as is", without warranty of any kind.function im = step2line(nscales, ampexponent, sze)    Octave = exist('OCTAVE_VERSION') ~= 0;  % Are we running under Octave?            if nargin == 3	Npts = sze;    else	Npts = 256;    end    x = [0:(Npts-1)]/(Npts-1)*3*pi;        im = zeros(Npts,Npts);    off = 0;        for row = 1:Npts	signal = zeros(1,Npts);	for scale = 1:2:(nscales*2-1)	    signal = signal + scale^ampexponent*sin(scale*x + off);	end	im(row,:) = signal;	off = off + pi/2/Npts;    end        figure    colormap(gray);    imagesc(im), axis('off') , title('step to line feature interpolation');        range = 3.2;    s = 'Profiles having phase congruency at 0/180, 30/210, 60/240 and 90/270 degrees';        if Octave	plot(im(1,:)) , title(s), axis([0,Npts,-range,range]), axis('off'); hold('on')	plot(im(fix(Npts/3),:)), axis([0,Npts,-range,range]), axis('off');	plot(im(fix(2*Npts/3),:)), axis([0,Npts,-range,range]), axis('off');	plot(im(Npts,:)), axis([0,Npts,-range,range]), axis('off');     	hold('off')    else   % MATLAB plotting	figure	subplot(4,1,1), plot(im(1,:)) , title(s), axis([0,Npts,-range,range]), axis('off');	subplot(4,1,2), plot(im(fix(Npts/3),:)), axis([0,Npts,-range,range]), axis('off');	subplot(4,1,3), plot(im(fix(2*Npts/3),:)), axis([0,Npts,-range,range]), axis('off');	subplot(4,1,4), plot(im(Npts,:)), axis([0,Npts,-range,range]), axis('off');    end