RE: [APML] ESO Tarantula CCD image

["Chris Schur" <cschur@cybertrails.com>]

Jerry, I make synthetic luminance frames all the time from three RGB or
tricolor film images for the LRGB combine.  You DO get a better signal to
noise in the final image when the image is converted to LAB color in this
fashion.  It is very substantial, and also allows you to process the L
portion with transfer fucntions that are not possible with a color image.

Chris Schur

Astrophotography: http://www.psiaz.com/schur/astro/index.html


-----Original Message-----
From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
Behalf Of Jerry Lodriguss
Sent: Thursday, June 13, 2002 10:16 PM
To: astro-photo@seds.org
Subject: [APML] ESO Tarantula CCD image


It appears the pros are using techniques developed by amateurs, which would
be something to be proud of, but the pros are doing it incorrectly!

Scroll down to the bottom of this page to the technical information about
the photos:

http://www.eso.org/outreach/press-rel/pr-2002/phot-14-02.html

It says:

>is an LRGB composite image, using a processing technique known as
>"Luminance Layering". The red, green and blue images were stacked for the
>Luminance (L) channel, yielding a black and white, high S/N-ratio image.
>In order to show details in the bright centre of the nebula as well as the
>much fainter outer filaments, a non-linear filtering technique known as
>"DDP" (cf. http://www.asahi-net.or.jp/~rt6k-okn/viewgrap.htm for more
>details) was applied to the Luminance image. In parallel, the three colour
>channels were combined in the usual way into an RGB colour image. The
>colour information from the latter image was then copied onto the
>Luminance image.


Notice they are making the luminance layer out of a combination of the red,
green and blue filtered images.

I wonder if they know they are not gaining anything by doing this because
they did not shoot a separate high resolution luminance channel with a
higher signal to noise ratio to start with.

The signal to noise ratio from combining the RGB channels is the same if
it's color, or if it's black and white.

I'm not talking about applying Okano's DDP to the image.

Maybe someone should clue them in... <G>

Jerry

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

Sports Photography: http://www.astropix.com/SPORTSPIX/INDEX.HTM


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