Hi - this is just in the bits of code that test for whether the USAN
(local neighbourhood of similar valued voxels to the centre voxel) is
empty or not - these constants represent the value which is generated by
the centre voxel itself - which clearly isn't of interest in judging
whether the USAN is "empty" - hence this value is first subtracted from
the USAN sum. By default, if the USAN is empty, then the algorithm reverts
to the median.
Cheers, Steve.
On Mon, 25 Jul 2005, Martin Kavec wrote:
> Hi,
>
> I think I address this question mainly to Steve Smith, the author of Susan
> filter.
>
> I have a student, who is implementing Susan smoothing filter using ITK
> (www.itk.org) image processing library. In trying to understand FSL
> implementation he studied susan_smooth.c. However, he can not figure out, how
> were some constants determined:
>
> a) 10000 at lines 386, 387 and 390
> b) 100 at lines 427, 428, 431
> c) 1000000 at lines 699, 700 and 703
> d) 20000 at lines 966 and 1156
> e) 200 at lines 1036 and 1230
> f) 2000000 at line 1363
>
> These constants are always used near-by
> if ( use_median ), so I assume the logic is similar.
>
> I would appreciate your explanation. Thanks in advance.
>
> Cheers,
> Martin
>
--
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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