Reducing Bloated Stars and Star Halos In PixInsight

Particularly when using a mono camera, certain filters such as OIII or SII will give bloated stars. In this quick guide, I'll be showing you how to reduce those pesky bloated stars and halos.

I tend to do this in the non-linear stage after all of my noise reduction and masked stretch.

• First, make a mask using the range selection tool. Change the lower limit to 0.6-0.8, only leaving the star cores left.

Make a clone of the range mask and call one A and the other B

Let's work on A first. This will be to protect the star cores

• Open up convolution and change the StdDev to 3 in the parametric tab and apply it to mask A

• Now apply a histogram transformation and change the highlights value to 0.7-0.8 to brighten it up a little

Repeat this for mask B, changing the StdDev value to 20 and then the highlights to 0.04

Next, open PixelMath, make sure that use a single expression is checked and type in B-A to remove the star cores from the halo mask

You should get a result looking something like this.

Lastly, open ATrousWaveletTransform. Change the layers to 12 and experiment deselecting the detail layer on layers 6 to 11. It's recommended to use the preview around some affected stars to see the result. You don't want it to have any dark ringing

I hope you found this helpful. If you have any questions, please don't hesitate to contact me.

Matt