%% Shows Sinogram explicity and demonstrates that 
%  unfiltered backprojection is a convolution.
N = 256;
x0 = 192; 
y0 = 192;
    im = zeros(N);
    im(x0,y0) = 1;
figure(1);clf;
subplot(2,2,1); imagesc(im);title('Original Image');
%%

ang = [0:179];
g = radon(im,ang);
figure(1);subplot(2,2,2); imagesc(g); title('Sinogram')

%% now show moving pixels and sinograms

for x0 = 16:8:240
    for y0 = 16:8:240
        im = zeros(N);
        im(x0,y0) = 1;      
        g = radon(im,ang);
        
        figure(1);clf;
        subplot(2,2,1); imagesc(im);title('Original Image');
        subplot(2,2,2); imagesc(g); title('Sinogram')
        bg = iradon(g,ang,'linear','none');
        subplot(2,2,3);imagesc(bg);title('Unfiltered BackProjection');
 
        pause(0.1);
    end
end