Removing the background of a wide field shot

[Roy Easto]

Just a post to ask what other people have as a solution to a particular
image processing problem.

The problem is to remove sky background from a wide field image, say a
20mm - 200mm camera lens where there is a light gradient across the
image. So without removing the background, if you brightness stretch the
image to show fainter stars you will burn out part of the image and
blacken other parts.

Flat fields are done but as the gradients are real in the sky they do
not disappear. I have tried generating gradients programmatically but
without great success. Finally I asked ChatGPT to write me a program and
this is what I use now. It takes the image, identifies and removes the
stars, replaces the hole with surrounding levels and then does a large
Gaussian blur on the whole image to create a background for subtraction
from the original image.

The attached image is a side by side comparison of the raw vs processed
image after flat fielding and background generation and subtraction. The
image is a 5 second exposure at f1.4 with a 50mm lens and mag 10 stars
are just visible.

I'm wondering if other people use functions within PaintShopPro or
something else?

Roy

[drja...@aol.com]

Roy

Your version looks as good to me as the results from apps specifically made for the purpose. 

Starnet2 in Pixinsight will remove the stars (and then one uses a mask to protect the nebula/galaxy if that's the target) leaving the background to work on.  

I'm expect there are free alternatives on the web, maybe even Starnet.  

The much pushed by influencers alternative is Russell Croman's Star Exterminator (which saves the stars to add back later)  at some considerable cost.

James

Sent from AOL on Android

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