[ITK] Valid FFT Sizes

[Cory Quammen]

Tobias,

Indeed, the prime factorization of each dimension needs to consist of 2s,
3s, and 5s, which is indeed different from being a multiple of 2. 416 has
13 as a prime, but 60 is fine.

You could pad up to 432 = 2^4 * 3^3, you don't need to pad all the way up
to 512.

Cory

On Thu, Sep 17, 2015 at 7:10 AM, Wood, Tobias <tobias.wood at kcl.ac.uk> wrote:

> Hello,
>
> I am trying to FFT a moderately large 3D image but am receiving a
> contradictory error message:
>
> itk::ERROR: VnlForwardFFTImageFilter(0x3038500): Cannot compute FFT of
> image with size [416, 416, 60]. VnlForwardFFTImageFilter operates only on
> images whose size in each dimension is a multiple of 2, 3, or 5.
>
> All the image dimensions are a multiple of 2!  Are the dimensions
> restricted to be powers of 2/3/5 instead of multiples?
>
> I can pad the image out to a sensible size (e.g. 512x512x64), but would
> like to know if there are any other restrictions I should be aware of
> before going around in circles?
>
> Thanks,
> Toby
>
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>



-- 
Cory Quammen
R&D Engineer
Kitware, Inc.
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