Radon Transform reducing the number of parallel beams

Hi,

I am trying to understand different filters' and other things' effects on Radon Transform by using MATLAB. First I upload an image, then take its Radon transform with radon function and then reconstruct it with iradon function.

Now I wanted to see the difference between undersampling the projection data by reducing the number of parallel beams by a factor of 4 and reducing the number of rotation angles by a factor of 4. However according to what I understood from radon and iradon functions' descriptions, I can only change the number of rotation angles. Is not it true? If not, what is the way to do it?

Here is what I do to decrease the number of rotation angles by a factor of 4:

      I = imread ('asdasd.tif'); 
      Rad = radon (img,0:4:179); 
      I_ram = iradon(Rad,0:4:179,'linear','Ram-Lak'); 
      I_ham = iradon(Rad,0:4:179,'linear','Hamming');

Answer 1

[Matt J]

      I = imread ('asdasd.tif'); 
         N=length(I);

      Rad = radon (img,0:4:179);
         Rad=Rad(1:4:end,:)

      I_ram = iradon(Rad,0:4:179,'linear','Ram-Lak',N); 
      I_ham = iradon(Rad,0:4:179,'linear','Hamming',N);