[This is just one of many articles in the author’s Astronomy Digest.]
No lenses are perfect and brighter stars near the corners of the image can show a form of coma making them look like little seagulls. It is possible to make a brush tool which keeps the central part of the distorted star present, but overwrites the surrounding ‘wings’.
Makinga star repair brush tool in Adobe Photoshop:
Make a new blank image 500 x 500 pixels in size.
Use the elliptical selection tool to make a circle ~300 pixels in diameter centrally within it and paint its interior black.
Remove the selection and apply a Gaussian blur with a radius of 15 pixels to blur the black disk edges.
At the centre of the black disk make a circular selection of ~80 pixels across and paint its interior white. Remove the selection.
Make a circular selection surrounding this of ~150 pixels across and apply a Gaussian blur of ~12 pixels. This blurs the edges of the white disk and will define how ‘sharp’ the repaired stars will appear. If too sharp, the blur radius should be increased. Remove the selection.
Under ‘Edit/ Define Brush Preset’ make this into a brush called ‘coma’.
If the coma brush is selected (with a double click so that the left and right square bracket ([ ]) keys can be used to control its size) one can copy from a blank region of the adjacent sky and paste over the star with an appropriate size.