title: MATLAB How to implement a Ram-Lak filter (Ramp filter) in the frequency domain?
body: <p>I have an assignment to implement a Ram-Lak filter, but nearly no information given on it (except look at fft, ifft, fftshift, ifftshift).</p>
  
  <p>I have a sinogram that I have to filter via Ram-Lak. Also the number of projections is given.</p>
  
  <p>I try to use the filter </p>
  
  <pre><code>                      1/4              if I == 0
  
  (b^2)/(2*pi^2)  *     0                if I even
  
                        -1/(pi^2 * I^2)  if I odd
  </code></pre>
  
  <p>b seems to be the cut-off frequency, I has something to do with the sampling rate?</p>
  
  <p>Also it is said that the convolution of two functions is a simple multiplication in Fourier space.</p>
  
  <p>I do not understand how to implement the filter at all, especially with no b given, not told what I is and no idea how to apply this to the sinogram, I hope someone can help me here. I spent 2hrs googling and trying to understand what is needed to do here, but I could not understand how to implement it.</p>