Cleaning image before bkgnd extraction ?

[xfred53]

Hello,
The image Abell_2151.fit (see link at the end of this post) is the result of 25 frames calibrated, cos corrected, aligned and stacked.
This images has strong diagonal lines that were already on the raw frames (see eg Abell 2151-E-013.fit).
If I try to extract the bkgnd, I'm getting worse results.
Can I do something before in order to clean this image ?
Or is it a waste of time to process such images ?
Thank you for help.

https://www.dropbox.com/s/ci2f2vh9rwytjsu/Abell2151.7z?dl=0

[wvanreeven]

Strong diagonal lines indeed. Did you apply any flat fields, dark, bias? Those should take care of that.


HTH, Wouter

[xfred53]

These images are not from my scope. I took them form the iTelescope web service.
I tried to apply the dark master frame found on iTelescope but the lines remained.
(The bias did not help at all and there is no flat).