[Insight-users] Base question on derivative filters
Kishore Mosaliganti
kishoreraom at gmail.com
Tue Sep 8 16:19:55 EDT 2009
The resulting units are in world coordinates. You will not need to divide by
spacing. The sigma is also in world coordinates.
Kishore
On Tue, Sep 8, 2009 at 11:49 AM, Gomez Herrero, Alberto <
alberto.gomez-herrero at philips.com> wrote:
> Hello all,
>
>
>
> this is a question regarding derivative filters in general and the
> RecursiveGaussianImageFilter in particular.
>
>
>
> When we compute, say, the first order derivative of, say, a 2D image “ I“
> we get two images of the same size, “Ix”, and “Iy”. My question is, the
> resulting value (i.e. the Ix and Iy gray levels) is expressed in what
> units?, I mean, if the gradient is defined as increment_of_gray_level /
> increment_of_distance_in_world_coordinates, everything is ok; but if this
> filter works as a simple pixelwise convolution mask, then the gradient is in
> increment_of_gray_level / increment_of_pixels. In that case, I need to
> divide by the spacing to get the right units.
>
>
>
> I guess this is a very basic question, but I really need to make sure that
> this filters work as the first definition. I can’t find it in the code, I
> only know that the sigma for the smoothing is in world coordinates though…
>
>
>
> Anyone can clarify this please?
>
>
>
> Thanks,
>
>
>
> Alberto
>
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