Hi,
2.355 is quite good! See, for example,
http://mathworld.wolfram.com/GaussianFunction.html
for the relationship between sigma and FWHM.
Cheers-
Andreas
________________________________
Von: FSL - FMRIB's Software Library im Auftrag von Peter Fried
Gesendet: Fr 20.07.2007 15:46
An: [log in to unmask]
Betreff: Re: [FSL] Spatial Smoothing in Command-line
Thanks Steve and Dan.
My confusion was trying to reconcile the report.log output with the
gui/command-line instructions.
-Pete
> Hi Pete,
> I do not know what math is used to calculate the spatial smoothing
> sigma for ip, but you can see what FSL calculates by trying a couple
> of smoothing widths and then looking at the report.log...I have found
> this identifies a constant relationship.
> For example, in my analyses I see that 4mm smoothing involves -s
> 1.69851380042 , and 8mm smoothing involves 3.39702760085. This shows
> that dividing the desired mm smoothiing by 2.355 gives you the sigma
> FSL uses ...I am not sure whether any of the other variable
> preprocessing parameters alters this number.
> Dan
>
>
>
>
>
> On 7/20/07, Steve Smith <[log in to unmask]> wrote:
>> Hi - please see the usage description that you get when you type
>> "ip". The -s flag is followed by the spatial sigma width - i.e.
>> approx half of the FWHM. Hence you would want to specify 3 here to
>> get 6mm FWHM.
>>
>> Cheers.
>>
>>
>>
>> On 19 Jul 2007, at 22:44, Peter Fried wrote:
>>
>> > Hi All,
>> >
>> > To perform gaussian spatial smoothing of 6mm FWHM in the command-
>> > line, do
>> > I simply run the command:
>> >
>> > ip <input> <output> -s 6
>> >
>> > Or do I need to calculate a different value for -s?
>> >
>> > Also is the threshold value arbitrary?
>> >
>> > Thanks.
>> >
>> > -Pete Fried
>>
>>
>> ------------------------------------------------------------------------
>> ---
>> Stephen M. Smith, Professor of Biomedical Engineering
>> Associate Director, Oxford University FMRIB Centre
>>
>> FMRIB, JR 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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