Star reduction procedure in Gimp 2.10

 Star reduction procedure in Gimp 2.10

The procedure followed here have been carried out on  a cropped Seestar S50 image of the bubble nebula. It is of average quality but serves nicely to demonstrate the procedure.

Animation showing the before and after star reduction

The star reduction procedure is detailed below

 

Tools

    Selection Tools

        By Colour Select

        In Tool Options

            Threshold 40

            Click on a star

                Select

                    Grow

                    Grow selection by 3 pixels

                Select

                    Feather

                    Feather selection by 4 pixels

                    If some nebulosity has been selected as well as stars

        Then use Free select tool with CTRL pressed and outline the area to be excluded from the selection

        Filters

            Distorts

                Value Propagate...

                    Mode More Black

       Select

       None

 

 

Note: The numbers 40, 3 and 4 in bold above will work but are guideline values that can be experimented with.

The above procedure is carried out in the Gimp and is shown by the following screenshots.

Click on a screenshot to get  a closer view

Tools > Selection Tools > By Colour Select

Threshold = 40

Click on a star to select and note that a small amount of the bubble nebulosity has also been selected

Select > Grow > Grow selection by 3 pixels

The selections have grown by 3 pixels

Select > Feather > Feather selection by 4 pixels

Use Free select tool with CTRL pressed to exclude the area of nebulosity that had been selected

Filters > Distorts  > Value Propagate

Mode > More Black

Preview disabled

Preview enabled

Select > None

Stars have been reduced

The original animation of before and after star reduction

This article was inspired by two YouTube videos, one by Ruzeen Farsad and the other on the AstroOnBudget channel