[Insight-users] Negative values inside a shape using SignedMaurerDistanceMapImageFilter

[Gaëtan Lehmann]

Hi,

In the SignedMaurerDistanceMapImageFilter, the object are not defined  
by their bourders, but by the label of their pixel. All the pixels  
above 0 are inside the object, the other are outside.

In your example, the center of the shape is *outside* the object, and  
that's why you get positive values. To get negative values, you have  
to fill your object, for example with the  
GrayscaleFillholeImageFilter, before computing the distance map.  
Something like:

o o o o o o o o
o o o x x o o o
o o x x x x o o
o o x x x x o o
o o o x x o o o
o o o o o o o o

Will give what you want.

Regards,

Gaëtan




Le 30 août 07 à 20:00, Blue Moon a écrit :

> Hi,
>
> I am new to ITK and I am trying to use  
> SignedMaurerDistanceMapImageFilter to compute the distance map  
> around a shape. My problem with this filter is I always get  
> positive values inside the shape. An example is given below:
>
> For an input shape o o o o o o o o
> o o o x x o o o
> o o x o o x o o
> o o x o o x o o
> o o o x x o o o
> o o o o o o o o
>
> I am expecting something like:
> 3 2 1 1 1 1 2 3
> 2 1 1 0 0 1 1 2
> 2 1 0-1-1 0 1 2
> 2 1 0-1-1 0 1 2
> 2 1 1 0 0 1 1 2
> 3 2 1 1 1 1 2 3
>
> but I get +1 instead of -1 for the internal pixels. When I set the  
> internal 'o' to 'x' in the input image, I get '0' for these positions.
> Is this what the filter is designed to produce, or I've done  
> something wrong?
> Any suggestions on how to use this filter will be much appreciated.  
> Thanks in advance.
>
> BM
>
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--
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr



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