%% edgedet.m 
%% demonstrate edge detection
%% S. Allen Broughton - 7 Mar 01

% get image from MATLAB image
load('trees');

% show original image
figure(1);
imshow(real(X),[]);
title('original image');
drawnow;
 
% construct convolution functions
[m,n] = size(X);
g = [1 -1];  
h = [1; -1]; 


% construct convolution matrices as sparse matrices
Wg = circconv2(X,g);
Wh = circconv2(X,h);
  
% show transformed images
figure(2);
imshow(Wg,[]);
title('horizontal difference filtering');
drawnow;

figure(3)
imshow(Wh,[]);
title('vertical difference filtering');
drawnow;

figure(4)
imshow(abs(Wg)+abs(Wh),[]);
title('edges');
drawnow;

% truncate and show edges
figure(5)
W = abs(Wg)+abs(Wh);
Y = zeros(size(W));
M = max(W(:));
J = find(W > .2*M); 
Y(J) = W(J);
imshow(Y,[]);
title('edges after thresholding truncation');
drawnow;