Stars artefacts aft...

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Stars artefacts after creating a mosaic  


Main Sequence Star Customer
Joined: 1 year ago
Posts: 49
February 23, 2020 12:03  


I'm working on a little 2x2 mosaic and I've noticed strange artefacts in the stars shape : scare center, dark borders...

The single stacked frames don't show any artefact, only the mosaic. See the joined picture : 300% zoom, single stacked frame on the left, mosaic on the right side).

By looking at my previous mosaics, the artefact is also there.

So I think the issue might come from the parameters used, or not 😀 

Here are my usual settings :

3 -  stars count at 5000

4 - quadrilaterals, scale 1 to 10, DDC and same camera and optic checked, mosaic registration mode and projective

5 - advanced mode and defaults parameters

6 - mainly defaults, full mode, LNC 1-3, MBB 15, no rejection, no drizzle




Thanx for your feedback.



This topic was modified 1 month ago by Dav78

White Dwarf Customer
Joined: 2 years ago
Posts: 17
February 23, 2020 15:30  

300% - that is some pixel peeping 😊 

Only thing that comes to mind immediately - you really need 5000, I usually use 3000 at best (although I don't think this has anything to do with your problem.

What is your imaging gear ?

Dav78 liked
Quasar Admin
Joined: 3 years ago
Posts: 2366
February 24, 2020 20:48  

Hi David @dav78,

It looks to me like there is downscaling in play together with Lanczos data interpolation. Are you creating the mosaic using frames with different image scales?

The artefacts migh be avoided by

  • using another data interpolation filter, like Cubic B-Spline, or
  • preventing the possible downscaling
  • or using drizzle integration instead of non-drizzle integration, just enable drizzle, use scale 1.0, droplets of 1.0 and the tophat kernel, that should really give you better stars 😉




Main developer of Astro Pixel Processor and owner of Aries Productions

Dav78 liked
Main Sequence Star Customer
Joined: 1 year ago
Posts: 49
February 24, 2020 21:40  


@einari, yes 300% is definitely a huge pixel peeping 😉, the purpose was to show the issue. But looking at the full mosaic, it's not so bad, but some stars have a strange shape. My gear is A7S modified + TS Star 71.

@mabula-admin, thanx for your quick feedback ! The different pictures were just cropped to avoid bad sides, but they have the same scale, at least I think. I will try your solutions and be back here soon 😀 

Main Sequence Star Customer
Joined: 1 year ago
Posts: 49
February 25, 2020 00:17  


I tried a few things :

1 - lanczos3 as usual, with the issue

2 - Cubic-Spline : the stars are perfectly round, but much bigger, and very soft, as the background

3 - Drizzle 1 : the better result, with stars just a little bigger than the single stacked frame, but with a softer background

4 - Billinear : similar to drizzle 1, but the stars seem to be a little bigger.


What do you think about those results Mabula ?