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Thom,
No stupid questions, that's how we learn.
Lord knows I've gained much from this group, so let me see if I can
help.
The answer to your question is obvious when we
examine just what is this stacking process. When we 'stack' images we are
applying some mathmatical function to the pixels of each image in the
stack. Typically pixels at the same relative coordinates are averaged or
added. Now I think the answer to your question becomes clear. If you
average the same value for any sample size you get the same number. Also
if you add the same relative values to themselves the values will increase, but
will do so proportionately and will not give any better signal to noise ratio
and will likely end up clipping on the white end.
But lets look at what happens when we 'stack' using
different images of the same subject. When the relative pixels are
averaged, say, the pixels of our subject are more consistent than the backrouund
noise and tend to clean up. The result is better signal to noise
ratio.
Jerry does a much better job of explaining this on
his website along with a scientific study of various stacking techniques:
http://www.astropix.com
Carpe Noctem, Frank
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