[Insight-users] GradientImageFilter vs GradientRecursiveGaussianImageFilter

[Pieter Vos]

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