%%
%% Lecture 6, CNS186 Winter 2002
%% 
%% (c) Pietro Perona, California Institute of Technology
%% 





%%
%% Generate left and right images
%% These are random dot stereograms (see Bela Julesz's work)
%%
left_image = round(rand(64,64));
right_image = left_image;
right_image(25:40,25:40) = left_image(25:40,8+[25:40]);
right_image(25:40,41:48) = round(rand(16,8));

%% Display left and right images
%% You can try and free-fuse them
figure(1);
subplot(1,2,1); imagesc(left_image); colormap(gray); title('Left image');
subplot(1,2,2); imagesc(right_image); colormap(gray); title('Right image');


%% Display line 32 from the left and right image.
%% Notice that they are identical on the sides and shifted
%% with respect to each other in the center.
figure(2);
OFFSET = 0.01;
LINE = 32;
li = left_image(32,:);
ri = right_image(32,:);
plot(li-OFFSET,'r'); hold on;
plot(ri+OFFSET,'g'); hold off;
title('Scanline n. 32 in left and right images');

%%
%% Find correspondence
%%

%% Generate receptive fields of 3 types of cells
kk = [1 2 1]; for i=1:2, kk = conv2(kk,kk); end;
k0 = kk;  k0 = k0 / sum(abs(k0));
k1 = conv2(k0,[-1 0 1]); k1 = k1 / sum(abs(k1));
k2 = conv2(k0,[1 -2 1]); k2 = k2 / sum(abs(k2));
figure(3);
subplot(1,3,1); plot(k0); title('Gaussian kernel');
subplot(1,3,2); plot(k1); title('Gaussian 1^{st} derivative kernel');
subplot(1,3,3); plot(k2); title('Gaussian 2^{nd} derivative kernel');


%% Filter the two scanlines with the 2 derivative filters and compare
%% in order to obtain correspondence.
li_0 = conv2(li,k0,'same');
li_1 = conv2(li,k1,'same');
li_2 = conv2(li,k2,'same');
ll = [li_0;li_1;li_2];
ri_0 = conv2(ri,k0,'same');
ri_1 = conv2(ri,k1,'same');
ri_2 = conv2(ri,k2,'same');
rr = [ri_0;ri_1;ri_2];

for i=1:64, for j=1:64,
  DD(i,j) = norm(ll(:,i)-rr(:,j));
end; end;


%% Display places where the cells' responses are similar.
%% These places are good candidates for correspondence
THRESH = 0.01;
figure(4);
imagesc(DD>THRESH); colormap(gray);
title('Points where there is good correspondence');
xlabel('Left image coordinate');
ylabel('Right image coordinate');