Hi,
Actually, it is a little more complicated.
The highpass filter does a locally-Gaussian-weighted straight line fit
and subtracts this from the data. The main difference between this
and a standard Gaussian lowpass subtraction is that perfect linear
functions are totally removed whereas with a standard highpass
filter a linear function always leaves behind a small amount of high
frequency content (as a straight line has non-zero components at
all frequencies).
Apart from this behaviour with straight lines it acts very much like a
Gaussian lowpass subtraction.
All the best,
Mark
On 6 Jul 2011, at 07:02, Stephen Smith wrote:
> Hi - both lowpass and highpass apply a Gaussian lowpass convolution using the widths specified - and in the highpass case the lowpassed version is subtracted from the original to achieve the highpassing.
>
> Cheers.
>
>
>
> On 5 Jul 2011, at 21:48, Satrajit Ghosh wrote:
>
>> hi,
>>
>> is there some information on how temporal filtering is implemented in fslmaths?
>>
>> cheers,
>>
>> satra
>>
>
>
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> Stephen M. Smith, Professor of Biomedical Engineering
> Associate Director, Oxford University FMRIB Centre
>
> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
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