[Insight-developers] Re: FW: [Insight-users] GradientImageFilter vs GradientRecursiveGauss ianImageFilter

[Joshua Cates]

Hello,

This is fixed but I'm waiting until the dashboard is a little greener to
check it in.

Josh.

______________________________
 Josh Cates
 School of Computer Science
 University of Utah
 Email: cates@sci.utah.edu
 Phone: (801) 587-7697
 URL:   www.cs.utk.edu/~cates


On Tue, 30 Apr 2002, Joshua Cates wrote:

> Hi,
>
> I see the confusion now.  Since DerivativeOperator is being used in
> GradientImageFilter as a convolution kernel, it should be flipped across
> all of its axes before sweeping through the image and taking inner
> products.  This will make the difference in sign for a first derivative.
>
> I seem to have neglected to add a method in NeighborhoodOperator to do
> this axis flipping, which would be very handy; so I'll add one and fix
> GradientImageFilter tomorrow.
>
>
> Josh.
>
> ______________________________
>  Josh Cates
>  School of Computer Science
>  University of Utah
>  Email: cates@sci.utah.edu
>  Phone: (801) 587-7697
>  URL:   www.cs.utk.edu/~cates
>
>
> On Tue, 30 Apr 2002, Miller, James V (Research) wrote:
>
> > Josh,
> >
> > The GradientImageFilter uses the DerivativeOperator.  Is this filter using the
> > DerivativeOperator incorrectly? Or are the coefficient signs flipped?
> >
> > Jim
> >
> > -----Original Message-----
> > From: Pieter Vos [mailto:pieterv@nat-239.azn.nl]
> > Sent: Thursday, April 25, 2002 5:55 AM
> > To: insight-users@public.kitware.com
> > Subject: [Insight-users] GradientImageFilter vs
> > GradientRecursiveGaussianImageFilter
> >
> >
> > Hello,
> >
> > I compaired the outputs of the filter GradientImageFilter and the
> > GradientRecursiveGaussianImageFilter.
> > Both filters had the same 3D image: a black image with a white spot in the
> > middle. The vectoroutputs however, where not the same:
> >
> > The vectors of the GradientImageFilter where pointing away form the spot.
> >
> > ------------------
> > |
> > |	^
> > |	|
> > |    <-   ->
> > |    <-   ->
> > |       |
> > |
> > |
> > ------------------
> >
> > And the vectors of the GradientRecursiveGaussian where pointing to the
> > white spot:
> >
> > ------------------
> > |
> > |
> > |        |
> > |    ->     <-
> > |    ->     <-
> > |        ^
> > |        |
> > |
> > ------------------
> >
> > The second picture is as how it should be.
> >
> > So, am I forgetting some basic theory (and should I study again)
> > or should the outcome of the GradientImageFilter not be the opposite?
> >
> > Please help.
> >
> > Greetings,
> >
> > --
> > Pieter Vos
> > UMC Radboud Nijmegen
> > The Netherlands
> > mailto:pieterv@radiology.azn.nl
> >
> > _______________________________________________
> > Insight-users mailing list
> > Insight-users@public.kitware.com
> > http://public.kitware.com/mailman/listinfo/insight-users
> >
>
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