↓ 8 callersMethodGetFrequencyBin* Image Index [0, N - 1] returns [0 to N/2] (positive) union [-N/2 + 1, -1] (negative).
* So index N/2 + 1 returns the bin -N/2 + 1.
* If first
Modules/Filtering/ImageFrequency/include/itkFrequencyHalfHermitianFFTLayoutImageRegionConstIteratorWithIndex.h:177