[Insight-developers] RecursiveMultiResolutionPyramidImageFilter

[sgerber]

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 <sgerber at cs.utah.edu> 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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> [3] http://www.cs.utah.edu/~sgerber/tmp/pyramids.zip