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RE: [APML] ESO Tarantula CCD image

Jerry, my understanding on how this works is that in an image, the grain is
essentially a luminance noise, and much less color data noise.  If I add the
R+G+B and say thats my new luminance, it will of course have much less noise
than any single frame.  That appears to be the secret, a standard RGB
combines the three channels in such a way that the noise is "colored" and
much more visible.  Some people even blur the RGB and combine with a R+G+B
luminance to make an even smoother but equally sharp image.  This is the
best I can explain it.  I have used it dozens of times, and done carful
comparisons.  It works.  You might try splitting an RGB 16 bit image in PS,
and make a Lab this way to compare.

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: Friday, June 14, 2002 12:17 PM
To: astro-photo@seds.org
Subject: RE: [APML] ESO Tarantula CCD image


At 01:24 AM 6/14/2002 -0700, you wrote:
>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.


Hi Chris,

I guess I really don't understand this then. How is this possible?

You make a luminance frame from three RGB images.

Or, you make a color composite from three RGB images and work on the L
channel in Lab.

Aren't they exactly the same thing?  If not, why not?

Jerry




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

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


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