FFT: How to select BW and frequency [message #9549] |
Mon, 21 July 1997 00:00  |
hahn
Messages: 108 Registered: November 1993
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Senior Member |
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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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