PixInsight Forum (historical)

PixInsight => Tutorials and Processing Examples => Topic started by: kerrywaz1 on 2011 July 03 15:22:37

Title: Star Elongation?
Post by: kerrywaz1 on 2011 July 03 15:22:37

Anyone have a tutorial or steps outlining how to fix some minor star elongation in PixInsight?

Thanks,

Title: Re: Star Elongation?
Post by: Nocturnal on 2011 July 03 15:30:32

Sure, find the source and eliminate it :)

Sorry, I have no idea how to reduce that effect except perhaps an erosion filter where you emulate the star shape with the matrix. I never considered that type of post processing worth the trouble so I haven't looked at it closely.

Title: Re: Star Elongation?
Post by: kerrywaz1 on 2011 July 03 15:44:59

Seems like I have seen a snippet on how to fix minor star elongation buried in another tutorial, but I can't remember which one.

--- Kerry

Title: Re: Star Elongation?
Post by: zvrastil on 2011 July 03 23:28:10

Hi Kerry,

you can try to fix/reduce star elongation with Deconvolution process. Choose Gaussian PSF, set "Aspect ratio" parameter to make PSF oval and "Rotation" parameter to orient it same way as your stars are elongated. Play with StdDev and Shape parameters -the resulting PSF (point spread function) should look like one of your unsaturated stars.

If you do need more info about how to apply Deconvolution, I'd suggest to look at this thread http://pixinsight.com/forum/index.php?topic=2727.0 (http://pixinsight.com/forum/index.php?topic=2727.0) - at the end of Page 1, there's great quickstart by Juan.

regards, Zbynek

Title: Re: Star Elongation?
Post by: Jack Harvey on 2011 July 04 07:03:24

I have done it using the Motion Blur PSF tab at the top of Deconvolution.  You will have to experiment with the two sliders.  Top one gives the amount of correction and of course the angle has to be set but I cannot remember if it is along the axis of elongation or 90 deg to the axis of elong.  Good luck.

Title: Re: Star Elongation?
Post by: Simon Hicks on 2011 July 05 00:04:23

Kerry,

Deconvolution with the shape parameters described above will work, but unfortunately can lead to hard edges to the stars. If this happens try using some MorphologicalTransform after deconvolution to soften the edges up again.

Cheers
           Simon

Title: Re: Star Elongation?
Post by: Carlos Milovic on 2011 July 05 09:16:30

Usually a mixed approach works very well. Perform deconvolutions and erosion filters, following the "drift". Try to iteratively achieve the final result, instead of one perfect step. Usually this procedure yields less artefacts, and a more pleasant result.