PixInsight Forum

PixInsight => Image Processing Challenges => Topic started by: tdgm on 2018 February 06 12:08:12

Title: Repair star core
Post by: tdgm on 2018 February 06 12:08:12
Hello everyone

Below you will see an image of a star zoomed in and if you look close the core is evident and a little darker than the rest of the star. How do I fix this situation. You will have to look close to see what I am talking about but it is there. It becomes more evident as you process the images. This image is just after Integration of a.n luminance image of 31x10 minute images.

Thanks for any suggestions you guys/gals can come up with.

Steve Herrman
Title: Re: Repair star core
Post by: RickS on 2018 February 06 12:57:12
You might find the 3DPlot script useful for inspecting the stars.  A star mask and a little blur (Convolution or remove some small scale layers with one of the Multiscale processes) should make an improvement.  I'd also put some effort into working out why it is happening in the first place...
Title: Re: Repair star core
Post by: ngc1535 on 2018 February 06 21:48:54
Perhaps just a sanity check (similar to Rick's suggestion- I can't see from the JPEG- but you should measure the actual value in the star cores. If it is "1" then congrats! This is a well known optical illusion. (I run into this all the time when processing.) If the value isn't one...but very close, simply lowering the white point by just a little bit (1-3 screen (8-bit)) levels usually takes care of this. It is basically a contrast issue, when you lower the white point, the background will become a little brighter- so you raise the black point, thus a contrast adjustment.


P.S. It is a similar effect to the Hermann grid illusion with stars basically being the intersections...  see: https://en.wikipedia.org/wiki/Grid_illusion