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negative return values after FFT [message #49458]

Wed, 26 July 2006 14:01

adisn123
Messages: 44
Registered: July 2006

Member

Hi,

I did FFT from spacial domain to frequency domain on an image of about
500 x 500 pixel size.

IDL> ft = FFT(image, -1)

After filtering job, it was inversly fourier tranformed back using
IDL> inverse = FFT(ft, 1)

When I printed "inverse", the values were complex numbers.

1. Aren't they supposed to real numbers since I tranformed back to
spcial domain?

When I only get real numbers, using
IDL> print, float(FFT(ft,1))
There were some negative values in the array (quite a lot).

For my understanding, the inversely fourier tranformed values should
represent the pixel values corresponding to individual pixel
coordinates in 500 x 500 size.
How do I interpret those negative pixel values?

Thanks.

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[Message index]

		negative return values after FFT By: adisn123 on Wed, 26 July 2006 14:01
		Re: negative return values after FFT By: news.qwest.net on Fri, 28 July 2006 15:46
		Re: negative return values after FFT By: adisn123 on Fri, 28 July 2006 12:52
		Re: negative return values after FFT By: James Kuyper on Fri, 28 July 2006 05:15
		Re: negative return values after FFT By: adisn123 on Thu, 27 July 2006 12:53

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