Sum or average?

Hello guys,

here is the beginning of my 2nd narrowband imaging project: IC1396

This is the h-alpha shot: it is composed of 37x15min subs 8)

However, I could not process all the images together, so I divided them into 3 batches and then averaged the results. I also tried to sum them, but the resulting image did not seem all that different. But, since the values seemed a bit strange (I got some 200,000 values 8O ), I decided to process the average.
Any advice on this procedure? Should I use the sum when I have a similar problem in the future? I forecast there will be more of these multi-subs images in my future and I would love to know how to go about it.

The set up is my usual: TEC APO180FL with FF & ST-L 11K

Thanks and ciao

Luca

Attached Image:

Here is a 100% crop of the trunk

Attached Image:

Hi Luca,
I like Sigma combine because it gives you the benefits of both SUM and Average. Plus it does some noise reduction too.

Luca,

Belissima! I hope I didn't murder that word in context or spelling

If I understand you correctly, you had to create three sub-masters (for lack of better description) from your original 37 (I'm guessing two batches of 12 subs and 1 of the remainder?). I believe you would sum the three sub-masters. The big values are to be expected, since any value that is saturated to the 65,000+ level will obviously sum to big numbers. As long as you save the final file in floating-point FITs, you should be good. I'm presuming that you used something like Sigma Reject to create each of the sub-masters?

HTH,
Eric