[ITK] Valid FFT Sizes

[Bradley Lowekamp]

Hello Toby,

Have you looked into the FFTPadImageFilter [1], this automatically pad the image as needed.

This error message may need to be improved/corrected. If I recall this may be a a restriction on the prime factorization of the image dimensions, not simply that the size is a multiple of one of those numbers but that they are the only valid number for prime factorization...

416 prime factorization is 2^5 * 13. Does not work since 13 is a factor
450 prime factorization is 5^2*3^2*2  ( eyeball a close number)

I think the FFTPad filter should help with this computation.

HTH,
Brad


[1] http://www.itk.org/Doxygen/html/classitk_1_1FFTPadImageFilter.html

On 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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