%NPRE435
%% generate the Modified Shepp-Logan phantom, with projection angles defined
%% in phi
P=phantom('Modified Shepp-Logan', 200);
phi=[0:8:179];
[RP,xp]=radon(P,phi); % Radon transform to get the projection data
 
%% Add Gaussian white noise (mean=1, standard-deviation=std) to the projection data
std=0.125; % standard deviation of the gaussian noise
RP_noisy=imnoise(RP/max(max(RP)), 'gaussian', std)*max(max(RP));
 
%% Display the noise free projection data
figure(1);
imshow(phi, xp, RP, [], 'notruesize');
colorbar;
 
%% Display the noisy projection data
figure(2);
imshow(phi, xp, RP_noisy, [], 'notruesize');
colorbar;
 
%% inverse radon transform to reconstruct the image from noise free data
I=iradon(RP, phi);
figure(3);
imshow(I);
colorbar;
 
%% inverse radon transform to reconstruct the image from noisy data
I=iradon(RP_noisy, phi);
figure(4);
imshow(I);
colorbar;

%% The Assignment:
%% Please modify this code to generate projection data using the
%% shepp-logan phantom:
%% (1) 0~90 degrees only with 1 degree steps
%% (2) 0~179 degrees with 8 degree steps
%% (2) 0~179 degrees with 16 degree steps
%% note that all projection data has added noise using the imnoise() function shown above.
 
%% Reconstruct the image using iradon() and please print 
%% (1) noisy projection data
%% (2) reconstructed images
%% (3) the code for generating the projection data and doing the reconstruction

%% Please repeat the above steps and chaging the noise standard deviation
%% to 0.25 (setting std=0.25) and print the results.