[Aavso-photometry] RE: average vs. median

[Tomas L. Gomez]

Thank you very much for all these useful and interesting replies!

> If you median-combine a group of images taken with even
> slightly different background brightness, the combination returns the image
> of middle brightness, with little or no reduction in noise and little or no
> rejection of any but the most extreme artifacts. You get around that by
> having the software normalize the images as part of the combining process.

That is right!. A couple of weeks ago I did a median combine of several
images and I saw this. This is specially bad when observing from a very
light polluted place, as I do. The background light varies very much from
image to image, and if you just do a median combine, you will just get
the image with middle brightness.

Furthermore, I was thinking that if there is a lot of light pollution
(due to cities or Moon), there will also be a strong gradient in the
background light, so just a normalization
might not be enough preparation to do a median combine.

-Tomas