Hi Brad
Thank you for your feedback and taking the time to look at the images.
I am fairly certain that the "bias" is introduced due to the subsampling
strategy used in the ShrinkImageFilter, if an average would be used the
bias would disappear.
-Sam
On 2013-07-17 11:51, Bradley Lowekamp wrote:
Hello Sam,
I looked at the images you provided here:
http://www.cs.utah.edu/~sgerber/tmp/pyramids.zip [3]
in Slicer3D. I would agree that test1 from the RecursivePyramid with
the shrink filter does not appear to align up correct. So you are
likely onto something.
What I have found useful for many of these types of geometric filters
is to create an image of points of the physical location of center of
the pixels, or a set of images if the filter in question doesn't
support the multi-component pixels. Then pass this through the
filter.
Aside from potential boundary conditions the the pixel values of the
output should still be the physical location of the pixel in the
output. This can create useful and definitive tests.
Brad
On Jul 17, 2013, at 11:15 AM, sgerber <[email protected]> wrote:
Hi
RecursiveMultiResolutionPyramidImageFilter behaves significantly
different when using UseShrinkImageFilterOff() vs.
UseShrinkImageFilterOn(). The default, UseShrinkImageFilterOn(), uses
for subsampling a single pixel ("top right" corner) which results, for
piecewise constant images, in image gradients being shifted in
physical space. Is this intended? It's not the behaviour I expected
when I used this filter. It is also not documented in the
PyramidFilter documentation or the ShrinkImageFilter that this is the
subsampling method used.
Thanks
Sam
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