[Insight-developers] FFT implementations handle spacing differently

[Kevin H. Hobbs]

>>             On 9/27/12 7:13 AM, "Bradley Lowekamp"
>>             <blowekamp at mail.nih.gov <mailto:blowekamp at mail.nih.gov>>
>>             wrote:
>>             However, I am
>>             >uncertain that this actually make sense, as the
>>             FFTForward filter does
>>             >converts from the spacial domain to the frequency this
>>             physical
>>             >information may not be very logical.
>>             >


It would be really nice if the transformed image had frequency units, or
log2 frequency units.

I for one do not know enough to calculate the precise meaning of a
position on the transformed image.

I do know that artifacts that show up in repeating patterns will show up
as a blob on the transformed image, and I can high or low pass filter an
image with a circular mask, after applying itkFFTShiftImageFilter.

What I cannot do is use the current units on the transformed image to
confirm that the blob I mask corresponds to the artifact that repeats
every 10mm.

I also cannot compare two FFTs of repeating structures, I'm thinking
sarcomeres, and say anything quantitative about what's different.

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