Same old dilemma: AVG or SUM?

Hello everyone,

I hope that everyone of you dear U.S. friends have had time to digest the Thanksgiving turkey cause I've got an old problem on which I'd like your advice.

I post 2 images of the Horsehead (I had time to add one more hour of data to my last image of the same subject): both are 6 20 minute subs, BUT one (image A) is a sum and the other (image B) is an average of the 6 subs. Both have been processed the same way: what is your opinion?
My opinions are:
1) I think that the average seems to be a little smoother than the sum, but I don't know why: even at 500% it is however hard to tell if it is true or it's only my impression.
2) The color seems more intense, in the sum and it should be because the sum should have a stronger signal and hence a stronger color.

I don't remember where but I read somewhere that if you have many images it is probably better to average, whereas, if you only have a few, it would be better to sum: can anyone help me on this? I believe that all the combined experience in this forum could be extremely helpful in solving this problem.

Ciao all and thanks for any suggestion you may have.

Luca

Attached Image:

It also depends on what your raw data is.

If your raw date is bright enough, then when you add it all together in a straight sum, you may oversaturate the highlights, and lose detail.

On the other hand, if you simply avarage, and you don't have enough range in your individual exposures, you will have to do more stretching than you would with a sum.

I think in general your rule about the more exposures you have the better averaging becomes holds true only if you have enough signal in the exposures that they don't need to be stretched as much later.

Alex