Processing or Hardware Issue?

Gents (and Ladies),

I have been processing some of my webcam images and have run into a problem after stacking. The attached image consists of a stack of 109 AVI frames from a 740 frame file that were taken through a C8 using a Logitech 4000 webcam and K3CCD tools then stacked in Registax v4.

Disregarding the fact that the planet is out of focus, the problem I am having are the diagonal bands from top left to bottom right that I keep getting across the image. I initially thought that it might be an issue with the Bayer matrix so I attempted to use Registax's debayering options and none of the four combinations (GR, BG, RG, GB) have removed the banding. When I magnify the image so the pixels can be clearly seen it looks as though the bands occur every six pixels rather than every four that I would expect with a debayering issue.

I have used the raw AVI by itself as well as with combinations of flats and darks to try to remove the banding but have been unable to make any headway. What is it that I am seeing here and how do I remove it?

Aaron

Attached Image:

Your gain is set too high. Try reducing gain and the bands sould go away.

Reducing the gain when you take the images might help,
as already suggested. You would need to take new
AVIs; these cannot be repaired.

I have sometimes seen banding like this due to
electronic interference. For example, if the
cable for the camera runs along the cable for
the drive motors. Best to keep the camera
cable well away from drive electronics, etc.

When you are aligning in Registax, do you use
a box which will just cover the planet and
no larger? Keeping the alignment box as small
as possible will help reduce the problem.

Sometimes I can repair minor banding in
Registax by setting the Pre-Filter to
Lowpass3 during the optimize step. But this
is probably beyond what can be repaired
that way. The idea here is to smooth-out
the bands during the image alignment. Otherwise
Registax tries hard to align the bands
instead of the planet. But that works best with
2-pixel bands; it won't do much for 6-pixel bands.

Aaron,

Try Iris:
http://www.astrosurf.com/buil/us/iris/iris.htm

Open the command console and type:
>fftd x y
>ffill 0
>save x
>ffti x y

Set the threshold window to 255 (top slider) and 0 (bottom).


See: Fixed pattern noise removal, about halfway down the page.
http://www.astrosurf.com/buil/iris/new410/new410_us.htm

This only works with black and white images. For color images, you will need to separate the RGB channels, and work with them individually.

Miguel

Attached Image: