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Re: FFT with NANs in an array [message #49439 is a reply to message #49342]

Thu, 20 July 2006 12:44

Steve Eddins
Messages: 9
Registered: July 2001

Junior Member

Steve Eddins wrote:
> adisn123@yahoo.com wrote:
>> Hi,
>>
>> I'm trying to fourier transform a spacial domain image to frequency
>> domain using FFT function in IDL.
>>
>> My image has quite a bit of NANs in an array, about 5%.
>>
>> When I use FFT into the image, it doesn't give me any errors, but when
>> I inversely fourier transform after
>>
>> filtering, it gives a little funky result.
>
> I would have expected you to get a VERY funky result. Since every
> output element of an FFT depends on every input element, I'd expect
> every output element of your result to be NaN.
>
>> How do I make FFT ignore NANs in their job or filtering?
>
> I think you'll need to explicitly replace the NaNs with 0s, like this:
>
> A(isnan(A)) = 0;

Whoops, forgot which newsgroup I was in, sorry. The above code line is
MATLAB syntax. Replace it with suitable IDL syntax.

--
Steve Eddins
http://blogs.mathworks.com/steve

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[Message index]

		FFT with NANs in an array By: adisn123 on Thu, 20 July 2006 11:00
		Re: FFT with NANs in an array By: Kenneth P. Bowman on Thu, 20 July 2006 19:48
		Re: FFT with NANs in an array By: adisn123 on Thu, 20 July 2006 17:08
		Re: FFT with NANs in an array By: Steve Eddins on Thu, 20 July 2006 12:44
		Re: FFT with NANs in an array By: Steve Eddins on Thu, 20 July 2006 12:42
		Re: FFT with NANs in an array By: Kenneth P. Bowman on Thu, 20 July 2006 12:24
		Re: FFT with NANs in an array By: R on Wed, 26 July 2006 15:47

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