Background substraction

Astrophotos taken in light polluted skies use to show a noisy gray background that should be avoided mainly for aesthetic reasons, and also to gain contrast in deep-sky objects. Using some image software like Paintshop Pro or Photoshop it is simple to correct the image in 4 steps:

1.- Make a copy of the image.

2.- Level the copy from zero to the highest background noise value. This way bright stars will appear as dim as background.

3.- Gaussian Blur the copy.

4.- Substract the copy to the original picture. You may add a small offset to the substraction if the background removal is very hard.

Here is an example with Orion constellation:

Background Substraction

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