拉冬变换，反变换

P=phantom(256);
figure,imshow(P);
title('image of a head phantom of Shepp-Logg');
theta1=0:10:170;
[R1,xp]=radon(P,theta1);
theta2=0:5:175;
[R2,xp]=radon(P,theta2);
theta3=0:2:178;
[R3,xp]=radon(P,theta3);
%figure,imagesc(theta1,xp,R1);
%colormap.title('R_{theta}(X\prime)');
%title('radon transform of 18 angles for Shepp-logan head phanto ');
%xlabel('\theta(degree)');
%ylabel('X\prime');
%set(gca,'Xtick',0:20:180);
%colormap(hot);
%colorbar;
%figure, imagesc(theta2,xp,R2);
%title('radon transform of 36 angles for Shepp-logan head phanto');
%xlabel('\theta(degree)');
%ylabel('X\prime');
%set(gca,'Xtick',0:20:180); 
%colormap(hot);
%colorbar;
%figure, imagesc(theta3,xp,R3);
%title('radon transform of 90 angles for Shepp-logan head phanton');
%xlabel('\theta(degree)');
%ylabel('X\prime');
%set(gca,'Xtick',0:20:180);
%colormap(hot);