[Insight-users] Base question on derivative filters

[Kishore Mosaliganti]

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
>
> ------------------------------
> The information contained in this message may be confidential and legally
> protected under applicable law. The message is intended solely for the
> addressee(s). If you are not the intended recipient, you are hereby notified
> that any use, forwarding, dissemination, or reproduction of this message is
> strictly prohibited and may be unlawful. If you are not the intended
> recipient, please contact the sender by return e-mail and destroy all copies
> of the original message.
>
> _____________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the ITK FAQ at:
> http://www.itk.org/Wiki/ITK_FAQ
>
> Follow this link to subscribe/unsubscribe:
> http://www.itk.org/mailman/listinfo/insight-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.itk.org/pipermail/insight-users/attachments/20090908/f0081548/attachment-0001.htm>