[ITK] [ITK-users] Questions on the itkANTSNeighborhoodCorrelationImageToImageMetricv4GetValueAndDerivativeThreader.hxx

[jiancong wang]

Hi guys,
I am working on replicating this image registration metric on gpu and has
some questions that I want to ask.

In both of the UpdateQueue functions I saw a line like this:
......
for ( SizeValueType indct = i; indct < hoodlen; indct += ( diameter +
NumericTraits<SizeValueType>::OneValue() ) )
......

Why the index is incremented by the diameter of the NCC window instead of
by 1? Isn't this suppose accumulate local pixel values for reuse purpose?
Also why there is only one for loop here? How do they handle 3D data in
this case?

I read the original paper and they are trying to cache the local sum value
(for example for a 7 by 7 window they are supposed to accumulate 7by1
column window, that each time it proceeds it only has to recompute the next
7by1 column instead of the full 7by7 window).

Any help is greatly appreciated! Thanks!
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