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

[Blue Moon]

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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