Square shaped black lines round stars.

[Astrogaby]

Hi guys, I am wondering what is the cause of the square shaped dark margins round the stars? The telescope used was the TS71 349mmFL with QSI690. This is a preview of an RGB image Astrodon filters and Baader UHC-S Filter for light pollution. The image was produced using standard procedures and the final noise reduction was done using MLT.  Any help would be greatly appreciated.
Gaby

[pfile]

check the registered subs for these artifacts, it may have been ringing caused by the StarAlignment interpolation algorithm. this can happen with undersampled images.

rob

[Astrogaby]

Will do thanks.

[rdryfoos]

check the registered subs for these artifacts, it may have been ringing caused by the StarAlignment interpolation algorithm. this can happen with undersampled images.

rob

  Then how do folks make wonderfull images at 3.5 arcsec/pix?  I have run into this issue to at 2.58 arcsec/pix and clamping does not solve it--I have to go to nearest neighbor to solve it--but that is not supposed to be as accuirate--correct?

[pfile]

drizzle can help with this problem, but as you've noted, besides that the only way to get around it is to use a different interpolation algorithm. the registration is accurate with other methods, but the registered images will be slightly less sharp. rather than nearest neighbor, you can try Bicubic Spline which is also pretty good and won't cause ringing to the extent that the default (lancosz-3) does.

rob

[Astrogaby]

I have redone the stacking using Bicubic spline and indeed the dark lines have gone however there are now red/blue strings in the image now. Any ideas as to cause?

[pfile]

pixel rejection settings in imageintegration should be able to take care of those.

rob