Re: [APML] Stacking Software

[Jerry Lodriguss <jml@astropix.com>]

At 12:05 AM 9/26/2002 -0400, you wrote:
>I am using Registar and I agree with Jerry. It is wondeful. After having said
>this I have some quetions about the stacking proccess. I had the idea that
>when you stack two or more images of the same object, the signal you have in
>the final composite is the sum of the signals from the original images,
>whereas the background is not the sum but something like an average. But after
>having used Registar for a while I have discovered that the "only" advantage
>of stacking is that the final image have less background but no more signal.
>So it is not the same a stack of two frames exposed half an hour each, that a
>single frma exposed for an hour. The stack of the two frmaes may have less
>backgound but the one hour single frma will have more signal. In conclusion
>the stacking proccess using programs such as Registar is not the panacea to
>obtain great images by simply adding a lot of underexpossed frames to get a
>beautifully color saturated, high contrast final composite. So my questions
>are: 1) Is there a balanced solution to get the maximum capabilities of the
>stacking proccess?:2) Is the diminishing of the backgound the only advantage
>of stacking several images?


You have it right.  Film is not CCD, and adding together 100 one minute 
exposures do not add up to 1 one hundred minute exposure.

After you register the images in Registar, there are different ways of 
combining them in Photoshop to boost the signal. See:

http://www.astropix.com/HTML/J_DIGIT/COMPEXP2.HTM

Some methods boost the signal while keeping the sky background noise the 
same. Others produce the exact equivalent of an average, which keeps the 
signal the same while reducing the sky background noise.

The answer to both of your questions, for film at least, is basically the 
same. Shooting multiple originals, each to the skyfog limit, and averaging 
them produces a great benefit in reducing the background noise, which then 
lets you boost the signal with a levels or curves adjustment.

Jerry

Astronomical photography: http://www.astropix.com




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