[Insight-developers] RecursiveMultiResolutionPyramidImageFilter

[Bradley Lowekamp]

This is certainly going to require more thought.

But if you shrink by 3, and your image is divisible by 3 does that appear to introduce a bias aswell?

I have a fiter which does average a "shrink" region which can be easily used in an external module[1]. Perhaps that would be more appropriate for your current application.

This issue has been debated about before. I'd be curious as to what you think of this [2] abandoned gerrit topic.

Brad

[1] https://github.com/blowekamp/itkBinShrink
[2] http://review.source.kitware.com/#/c/8179/


On Jul 18, 2013, at 10:54 AM, sgerber <sgerber at cs.utah.edu> wrote:

> 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