AFNI program: 3dDespike
Output of -help
Usage: 3dDespike [options] dataset
Removes 'spikes' from the 3D+time input dataset and writes
a new dataset with the spike values replaced by something
more pleasing to the eye.
* L1 fit a smooth-ish curve to each voxel time series
[see -corder option for description of the curve].
* Compute the MAD of the difference between the curve and
the data time series (the residuals).
* Estimate the standard deviation 'sigma' of the residuals
* For each voxel value, define s = (value-curve)/sigma.
* Values with s > c1 are replaced with a value that yields
a modified s' = c1+(c2-c1)*tanh((s-c1)/(c2-c1)).
* c1 is the threshold value of s for a 'spike' [default c1=2.5].
* c2 is the upper range of the allowed deviation from the curve:
s=[c1..infinity) is mapped to s'=[c1..c2) [default c2=4].
-ignore I = Ignore the first I points in the time series:
these values will just be copied to the
output dataset [default I=0].
-corder L = Set the curve fit order to L:
the curve that is fit to voxel data v(t) is
k=L [ (2*PI*k*t) (2*PI*k*t) ]
f(t) = a+b*t+c*t*t + SUM [ d * sin(--------) + e * cos(--------) ]
k=1 [ k ( T ) k ( T ) ]
where T = duration of time series;
the a,b,c,d,e parameters are chosen to minimize
the sum over t of |v(t)-f(t)| (L1 regression);
this type of fitting is is insensitive to large
spikes in the data. The default value of L is
NT/30, where NT = number of time points.
-cut c1 c2 = Alter default values for the spike cut values
[default c1=2.5, c2=4.0].
-prefix pp = Save de-spiked dataset with prefix 'pp'
-ssave ttt = Save 'spikiness' measure s for each voxel into a
3D+time dataset with prefix 'ttt' [default=no save]
-nomask = Process all voxels
[default=use a mask of high-intensity voxels, ]
[as created via '3dAutomask -dilate 4 dataset'].
-q[uiet] = Don't print '++' informational messages.
-localedit = Change the editing process to the following:
If a voxel |s| value is >= c2, then replace
the voxel value with the average of the two
nearest non-spike (|s| < c2) values; the first
one previous and the first one after.
Note that the c1 cut value is not used here.
* Despiking may interfere with image registration, since head
movement may produce 'spikes' at the edge of the brain, and
this information would be used in the registration process.
This possibility has not been explored or calibrated.
* Check your data visually before and after despiking and
[Hint: open 2 AFNI controllers, and turn Time Lock on.]
* This binary version of 3dDespike is NOT compiled using OpenMP, a
semi-automatic parallelizer software toolkit, which splits the work
across multiple CPUs/cores on the same shared memory computer.
* However, the source code is modified for OpenMP, and can be compiled
with an OpenMP-capable compiler, such as gcc 4.2+, Intel's icc, and
* If you wish to compile this program with OpenMP, see the man page for
your C compiler, and (if needed) consult the AFNI message board, and
++ Compile date = May 31 2013
This page auto-generated on
Mon Jun 3 08:37:21 EDT 2013