Is there any way to separate astronomical and instrumental objects?

Question

Here is an image of hcg79 taken from APO. I'm just curious if there is any way to separate astronomical and instrumental features in this picture?

Answer 1

A priori it is very difficult to distinguish the origin of any particular feature from just one image.

For that reason it is established workflow, especially in astronomical context, to create 4 kind of images:

• the light frame R. That's the actual image of what you are interested in
• the dark frame D. That's an exposure of identical length and at identical conditions, but with closed apperture. That takes care to assess the sensor reading in the absense of anything visible
• the bias frame B. That's a short-duration image which allows to assess the read-out noise
• the flat field F. That's an image of a perfectly white / grey area which allows to assess the different sensitivity of the individual pixels.

Then you can obtain the corrected image C via $ C = (R-D-B) \cdot \frac{<F - D - B>}{F - D - B}$

https://en.wikipedia.org/wiki/Flat-field_correction