Pixel Rejection

[Farzad_k]

Hello, Folks.

I am processing Andromeda using the fantastically well-written and presented online tutorial by Kayron - thanks, Kayron.

I know a little bit about what I am doing and am still trying to figure things out.

In case of pixel rejection during integration, I am not sure if I should necessarily do that. In the attached image of when I enable pixel rejection, it looks like a lot of data may be getting tossed out. Should I be concerned? Should I disable pixel rejection?

Thanks


Farzad

[Geoff]

After running ImageIntegration, look in the Process Console.  It will tell you what percentage of pixels have been rejected.  Then tweak sigma high and sigma low to get the best tradeoff between good noise reduction, low pixel rejection and removal of spurious data.
See here http://www.astrosurf.com/jordigallego/articles.html for dated but still useful info. Look at the 3rd article "Image Integration Techniques....."
Geoff

[RickS]

You're rejecting good data which will reduce SNR.  You should adjust the Sigma low and Sigma high sliders until what is left in the rejection maps is just the cold and hot pixels, cosmic ray trails, etc.  If you can see image features in one of the rejection maps then the slider value is too low.

As Geoff suggested, it is also useful to look at the total pixel rejection percentages.  After a while you'll get a good feel for what are reasonable numbers for your system.  It is worth checking through the percentages for the individual subs as well.  If you find a sub with especially high percentages you might want to take a closer look at it and perhaps consider dropping it from the integration.

The reference Geoff mentions is excellent too.  That's where I learned about tuning the rejection algorithm and parameters.

Cheers,
Rick.

[Farzad_k]

Thanks, I will definitely follow through.

Farzad

[Farzad_k]

So i am playing with the sigma value and when I get to 1, the background of the rejection becomes gray. I am assuming this is not a good thing, right?

[Farzad_k]

I think I was going the wrong way - I need to increase the number to make rejection less aggressive.

[RickS]

I think I was going the wrong way - I need to increase the number to make rejection less aggressive.

Correct.