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FFT: How to select BW and frequency [message #9549]

Mon, 21 July 1997 00:00

hahn
Messages: 108
Registered: November 1993

Senior Member

Hi,

I shot several photos of objects that were behind a curtain. Now I want
to eliminate the vertical and horizontal white streaks from the pictures.
The photos are stored as 24 bit tiff images. To get familiar with the
problem I read the blue image of one picture into the FFT demo of
IDL 3.01 and played with a band pass filter to get the vertical lines
of the curtain as good as possible, having the band width as low
as possible.

I manage to see the vertical lines in the filtered picture but when I
switch to the "band reject" function of the FFT demo, the lines
are not removed.

When I look at the first scan line of the photo I find 7 pixels that
are o.k. and 2 pixels that represent a part of the curtain. So the
following question comes up:

What is the relation of the number of pixels I want to change and
the bandwidth and frequency in the FFT program?

I selected the FFT demo as a first iteration because the streaks
made by the curtain are highly periodic. But, what other program can
be used instead of FFT?

Thanks for any help,

Norbert

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[Message index]

		FFT: How to select BW and frequency By: hahn on Mon, 21 July 1997 00:00
		Re: FFT: How to select BW and frequency By: Peter Mason on Wed, 23 July 1997 00:00

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