Removing stars from a deep-sky nebula target

Use a Photoshop plug-in to eliminate stars in an image of the Statue of Liberty Nebula

With the exception of targets like open clusters, stars are generally not the main feature of astro images. In fact, their presence can hinder us from teasing out nebulae and similar objects of interest. While some programs, like Photoshop, offer techniques to partly get around this, a new plug-in makes it much easier. In this article, I will look at the benefits of using StarX Terminator.

The plug-in StarX Terminator, by Russell Croman, has been trained to recognise and eliminate stars from an image, by using 'machine learning' (artificial intelligence). Once these have been removed, the image can be processed with full attention paid to the target. When the processing is complete, the stars can be put back in, or left out (see images, above).

The starless software revolution itself began with StarNet++, a free script for PixInsight. Several years later, StarX Terminator, a commercial plug-in, built by Croman's RC Astro, was introduced for Photoshop (and PixInsight). The software is compatible with Windows, macOS and Linux operating systems, and a free 30-day trial is offered (see www.rc-astro.com/ resources/StarXTerminator).

Why are stars such a challenge? For starters they are already bright, so you can damage them by 'stretching' (boosting) dimmer elements of the picture. Also, unlike the rest of the image, stars do not require sharpening or noise reduction - the removal of unwanted artefacts. If you are trying to process nebulae that lie within the Milky Way, it can be tricky to enhance their dim tendrils due to the stars in the field. You'll find that removing the stars makes processing so much easier.

Making life easier