aliasing1.m

aliasing in matlab by lrmaster,aliasing in matlab by lrmaster

% A program to demonstrate aliasing caused by sampling

clear all; % remove all previous data, etc
close all; % close anw windows

N= 128;   % set the size of the picture
[x,y] = meshgrid( 1:N ); % define sample locations

% make two signal pictures...
% ...One a slowly varying pattern...
w1 = 16;
pict1 = rem(x,2*w1) < w1;
% ...the other more rapidly varying
w2 = 2;
pict2 = rem(x,2*w2) < w2;

% now make a criss-corss sample grid
w3 = 2;
pict3 = (rem(x,2*w3 ) < w3) & (rem(y,2*w3 ) < w3);
ang = -5.0;
dummy = ones(size(pict3));
dummy = imrotate(dummy,ang,'bicubic');
pict3 = imrotate(pict3,ang,'bicubic');
pict3 = pict3.*dummy + ~dummy;
clear dummy; % delete the variable we no longer need

% make up a big picture as a target to put the others into
pict = ones( 2*N,2*N );

% place the signal pictures...
pict(1:N,1:N) = pict1;
pict(N+1:end,N+1:end) = pict2;

% ...and the sample grid...
[nr,nc] = size(pict3);
a = round(N/2);
b = a;
pict( a:(a+nr-1), b: (b+nc-1) ) = pict( a:(a+nr-1), b: (b+nc-1) ) .* pict3;

% then show the result
imshow(pict);