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Re: negative return values after FFT [message #49526 is a reply to message #49458]

Fri, 28 July 2006 15:46

news.qwest.net
Messages: 137
Registered: September 2005

Senior Member

<adisn123@yahoo.com> wrote in message
news:1154029980.397254.232310@h48g2000cwc.googlegroups.com.. .

> How do I interpret the "negative" spacial pixel values after inverse
> FFT?

Did you filter away the DC level? How does the mean of the
original compare with the mean of the filtered image.

What type of filter is it (low pass? high pass?).
I would be suprised to see a low pass filter extend the span of the data.
In fact, I would be surprised to see any filter extend the span of the data
by any appreciable amount.

Cheers,
bob

PS it seems like you solved the problem with "complex" values. I would
have mentioned to be sure your filter is "symmetric" about the origin in 2d
fourier
space, in order to ensure a real valued result.

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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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