Hi John mri_nlfilter implements what I think is the first example of nonlocal filtering/nonlocal means from this paper:

http://ieeexplore.ieee.org/document/745732/

it tries to avoid displacing edges as happens in straight Gaussian filtering

cheers Bruce

On Thu, 14 Dec 2017, John Anderson wrote:

Dear Dr Bruce, Kindly, I have question regarding the command "mri_nlfilter". I am sorry if my questions is simple, but I highly appreciate any explanation to improve my understanding.

I see in the man list of the command "mri_nlfilter" that it can apply Gaussian filtering and blurring kernell.  What is the difference between Gaussian smoothing and blurring. For example in PET images we used to smooth the images to improve SNR. Does blurring apply something similar and can be helpful to improve SNR.

Thanks for any clarification! J