Image Integration Problem with red spots at the edge of stars

[wkrispler]

Hi,

I have an issue with the image integration of 30 lights. Attached I have the integrated file without pixel rejection (integration_no_rejection), the
file using the Winsorized Sigma Clipping algorithm (default values) and the third one using the linear fit algorithm.

As you can see when using the Winsorized Sigma clipping on the edges of the three bright stars (marked in red) , red spots appear on the
right lower edge of the stars. Otherwise the image looks good. In the linear fit image those artefacts do not show up but the pixel rejection
is not sufficent in other aereas.

Any idea how I can get rid of those red spots?

Many thanks,

Wolfgang

PS: I know the stars are not round but that is a different problem

[vicent_peris]

Hi,

Have you tried to lower the sigma high of the linear fit clipping algorithm?


Best regards,
Vicent.

[Andres.Pozo]

Do these red pixels appear in the borders of the bright stars in the registered lights before the integration? If this is the case, the problem could be in the interpolation algorithm. You can try to change the value of the parameter "Clamping threshold" in ImageRegistration or BatchPreprocessing.

[wkrispler]

Good point Andres!
Yes, they also show up on the registered lights.
I will try to modify the clamping threshold.
Thank you so much!
@Vicent, thanks to you as well. The lowering of  the sigma high helped but created red pixels in other aereas of the stars!

[vicent_peris]

As Andrés points out, it could be the interpolation algorithm, specially if they appear in the subs. Those artifacts can happen when you have extremely high contrast from one pixel to another, as it could be the case in the corner of your stars. Because of this, the artifact cannot be effectively rejected, as it's located always in the same place. If it does not disappear by modifying the clamping threshold, then try to use drizzle in BPP.


Best regards,
Vicent.

[wkrispler]

Hi Vincent,

it does not disappear by lowering the clamping threshold not even when going down to 0. The "dark" pixel are already visible in the subs. I am always using drizzle as my
data is undersampled.
This did not help.

The funny thing is that these artefacts are not visble when I do the integration without rejection! They are clearly visible when I use Winsorized Sigma clipping. They are not
visible when using Linear fit but unfortunately other pixels which should have been rejected have not been rejected. I will now try Linear fit with different Low and High parameters and hope
to solve this problem this way.
Best Regards,
Wolfgang