[Insight-users] GradientRecursiveGaussianImageFilter

[Luis Ibanez]

Hi Zein,

Yes, this filter will compute the gradient
the image. If your image happens to contain
a binary object, the gradient values in the
border of the object will be an estimation
of the surface normals.  Note that only
and estimation is possible due to the discrete
nature of digital images.

Sigma should be expressed in physical units
for this filter. You probably want to use
at least 2x the largest pixels spacing.

Note that any surface features that are smaller
that 2 pixels will tend to disappear from the
gradient computation.

You may find useful to play first with the
GaussianFilter application in InsightApplications,
by looking at the individual components of the
gradient. That will be the safest way to find
an appropriate sigma value for your image.



Regards,


    Luis


---------------
salah wrote:

> Hello all,
> 
> I have a 3D itk binary image containing a segmentation,  and I want to compute the
> gradient at the outer surface of the segmented object.
> Is the (GradientRecursiveGaussianImageFilter) the right filter to use? or there is a 
> better one? BTW, I already used this filter, but found it very sensitive to the value of
> sigma and image spacing. Is there a rough method to guess the value of sigma ?
> 
> Many Thanks,
> Zein 
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