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72896Re: Calculating average brightness in an area of a fits image

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  • Stan
    Jun 2, 2013
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      --- 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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