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Re: negative return values after FFT [message #49541 is a reply to message #49444]

Thu, 27 July 2006 09:43

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

edward.s.meinel@aero.org wrote:
> FFT(*, *) can take REAL input and return a COMPLEX result; however, a
> COMPLEX input always returns a COMPLEX result. To get a REAL result you
> need to do:
>
> inverse = REAL(ABS(FFT(ft, 1)))
>
> Ed
>
> PS. The one-line solution: inverse =
> REAL(ABS(FFT(FILTERING_JOB(FFT(image, -1)), 1)))

OK - that's a different way of interpreting the message. I was
assuming, when he said that result was complex, that he wasn't
referring to the data type of the result, but to it's value: in other
words, that he was saying that the imaginary parts of the resulting
array had significantly non-zero magnitudes. With real-valued images,
and a properly defined filter, that shouldn't happen.

To the original poster (Google shortens your e-mail address to
'adisn...@yahoo.com', so I have no idea what I should call you):
Are you merely saying that the data type of the result was complex, or
are you making the stronger statement that the values in that result
had signficantly non-zero imaginary components?

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[Message index]

		Re: negative return values after FFT By: edward.s.meinel@aero. on Thu, 27 July 2006 07:22
		Re: negative return values after FFT By: James Kuyper on Wed, 26 July 2006 18:21
		Re: negative return values after FFT By: James Kuyper on Thu, 27 July 2006 09:43

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