72897Re: [ccd-newastro] Re: Calculating average brightness in an area of a fits image
- Jun 2, 2013That makes sense - thanks!
On Sun, Jun 2, 2013 at 11:01 AM, Stan <stan_ccd@...> wrote:
> --- Mark Striebeck <mark.striebeck@...> wrote:
> > But why is it that sky glow affects star colors differently...
> > thought of sky glow as a kind of filter...
> Sky transparency is a filter that can vary by color. Thus it may be
> necessary to adjust ratios based on air mass (sky alt).
> But sky glow is not a filter, the glow does not absorb or block photons.
> Sky glow is an imposition that is equivalent to a double exposure of the
> astro objects and a colored screen. So the way to neutralize sky glow is to
> subtract its contribution. Messing with color ratios to "balance" sky glow
> will necessarily distort the colors of the astro objects. (This is why most
> terrestrial photo software cannot correctly deal with astro image color.)
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