Re: [APML] Synthetic Luminance Channel for Film Images

["Volker Wendel" <volker@spiegelteam.de>]

Jerry,

> Man, I'm just trying to understand how a synthetic luminance could improve
> the s/n.

there was another question about this, answered by Stan Moore on the SBIG
list, maybe it helps:

***
> I really doubt that using LRGB with a synthetic L channel can
> increase the real S/N...

But it does seem possible to transfer some of the chromatic S/N to
the luminance, the penalty being lower chromatic spacial resolution
(a familiar characteristic of LRGB <g>).

For a weakly colored object (like a galaxy), combining the RGB
exposures into a greyscale produces S/N approx 1.7x higher than each
filtered exp. If you then make an LRGB and blur the color layer you
will remove most of the chromatic noise (at the expense of spacial
resolution).  So the resulting image may better resolve some dimmer
features, but without accurate coloration.

However, characterizing the human eye/mind response to RGB S/N poses
a serious difficulty in doing a complete anaysis of this technique.

Stan
***

I donīt know if you saw Rob Gentlers fine explantions about the use of two
synthetic L-channels (<G>), but here it is:
http://www.robgendlerastropics.com/LLRGB.html

Volker
www.spiegelteam.de




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