WIP: General itkFrequencyShrink / Expand #31
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WIP: Shrink is almost there, but the fix of nyquist band is still WIP. Fixing involves averaging of largest frequencies --largest taking into account the shrink factor-- in the input image, and placing in the nyquist band of the shrinked image. There are only nyquist bands in the dimension when the outputSize is even. A nyquist band exist in 2D, in 3D is a nyquist slice, in 1D is a point. When there are more even dimension, lower dimensions structures appear. In 3D, two even dimensions create 2 nyquist slices, and 1 nyquist band in the intersection. This band requires extra averaging. The same thing in 2D with 2 even dimensions, there is one point in the intersection that requires extra averaging. NOTE: Doing it general for NDimensions is verbose, dealing with positive and negative quadrants.
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WIP: General itkFrequencyShrink not requiring hermitian input.
Shrink is almost there, but the fix of nyquist band is still WIP.
Fixing involves averaging of largest frequencies --largest taking into
account the shrink factor-- in the input image, and placing in the
nyquist band of the shrinked image.
There are only nyquist bands in the dimension when the outputSize is even.
A nyquist band exist in 2D, in 3D is a nyquist slice, in 1D is a point.
When there are more even dimensions, lower dimensions structures appear.
In 3D, two even dimensions create 2 nyquist slices, and 1 nyquist band
in the intersection. This band requires extra averaging.
The same thing in 2D with 2 even dimensions, there is one point in the
intersection that requires extra averaging.
NOTE: Doing it general for NDimensions is verbose, dealing with positive
and negative quadrants.