NSGweight and image rejection - a white paint analogy

[rockenrock]

Hi John & others,

In the past I struggled where to draw the line in rejecting images with declining NSG weight.

Now I like to think of it as making white paint, where the most perfect image is pure white (no noise), but in reality the additional paint I am adding is not pure white (are noisy). Then I think of a low NSGweight image as dark grey paint being added to almost white. A few drops of dark grey is going to mitigate a lot of almost white paint.

So I am now more willing to cancel those lower level images whereas before my self-talk would say "it can't hurt" and almost all would go in the mix. 

Of course we are making black backgrounds not white, but the white paint analogy helps me be more honest. Some of my subs just aren't white enough (to noisy)!

 

Maybe someone else will have a bad apple analogy!

 

Roger

[John Murphy]

On 9/27/2023 at 6:11 AM, rockenrock said:

Hi John & others,

In the past I struggled where to draw the line in rejecting images with declining NSG weight.

Now I like to think of it as making white paint, where the most perfect image is pure white (no noise), but in reality the additional paint I am adding is not pure white (are noisy). Then I think of a low NSGweight image as dark grey paint being added to almost white. A few drops of dark grey is going to mitigate a lot of almost white paint.

So I am now more willing to cancel those lower level images whereas before my self-talk would say "it can't hurt" and almost all would go in the mix. 

Of course we are making black backgrounds not white, but the white paint analogy helps me be more honest. Some of my subs just aren't white enough (to noisy)!

 

Maybe someone else will have a bad apple analogy!

 

Roger

I love the white paint analogy, but as you suspected, the reality is a bit more complicated than that (which is why you asked the question). The white paint analogy is only valid if image weighting wasn't used.

 

This question arises quite frequently, so I have spent some time creating an extra page on my website to explain the main issues.

 

See the "Image weights" page on my website.

Regards, John Murphy

https://astroprocessing.com