AFNI Message Board

Dear AFNI users-

We are very pleased to announce that the new AFNI Message Board framework is up! Please join us at:

https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

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bob cox
July 29, 2003 08:44PM
A 3 point order statistic filter is used. That is, if the time series is

... a b c ...

then the value b is replaced by the following algorithm:

(a) Sort (a,b,c) into (p,q,r), where p <= q <= r.

(b) Output = 0.7*p + 0.15*(q+r)

This algorithm is applied to each point in the input time series to produce a new time series. It is not applied to points where any of (a,b,c) are being ignored.

Order statistic filters were originally defined to provide an intermediate type of filter between linear filters and median filters. I chose this particular filter back in 1993 (in the old program FD2) mostly because I liked the results visually. As I recall, these coefficients are optiimal for filtering time series which have Laplacian distributed noise.

bob cox
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Subject Author Posted

smooth ideal reference function

Philippe Goldin July 29, 2003 05:28PM

Re: smooth ideal reference function

bob cox July 29, 2003 08:44PM