[Insight-users] Strange values in BSplineDownsampleImageFilter

[Elena Pavlovskaia]

Hello,

I am using BSplineDownsampleImageFilter with
input image pixel type short, output type double.

I apply it to binary images with values
1 (in region) and 0 (out of region).

The resulting image has strange values inside the region,
far away from the boundary. Namely:

With spline order 1:
All the "in region" pixels at the pixel distance >= 5
from the boundary have value 0.9994. The "out of region"
pixels at the same distance have the value 0.0.

With spline order 3:
All the "in region" pixels have the value 0.9983.
The "out of region" pixels have the value 0.0.

With spline order 0:
All the "in region" pixels have the value 1.0.
The "out of region" pixels have the value 0.0.

I would expect that "in region" pixels have the value 1.0
for any spline order similarly to what I got for spline order 0.

Is the current behavior a bug or "as designed"?

Thank you,

Elena