LRGB technique query

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Astaunton
Asternaut
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Joined: Sat Mar 17, 2012 11:04 pm

LRGB technique query

Post by Astaunton » Sat Mar 17, 2012 11:12 pm

Hi There

Just a question about the LRGB technique:

On all the online sources I have found expounding on this technique, they imply that it can be used with commercial cameras that use an RGB colour filter array (CFA). What I can't figure out is how to get the luminance (L) frame - are they suggesting that I must remove the CFA in order to take the L frame? because I would probably break the camera if I tried to do that!!

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Chris Peterson
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Re: LRGB technique query

Post by Chris Peterson » Sun Mar 18, 2012 12:07 am

Astaunton wrote:On all the online sources I have found expounding on this technique, they imply that it can be used with commercial cameras that use an RGB colour filter array (CFA). What I can't figure out is how to get the luminance (L) frame - are they suggesting that I must remove the CFA in order to take the L frame? because I would probably break the camera if I tried to do that!!
You can't remove the CFA from any sensor: it is deposited directly onto the silicon by lithographic techniques.

In general, LRGB is not useful when using color cameras. The main reason for using LRGB is to reduce your total exposure time, since you can collect high resolution L data with a long exposure, and then low resolution binned data (2x2 or 3x3) for the color channels, which can tolerate much lower S/N when combined with the high S/N luminance. With a color sensor, this is impossible. Binned color images produce low resolution luminance- completely backwards from LRGB images through filters.

I've seen people who reported various processing techniques they identified as LRGB with color cameras, but they really aren't, and they don't offer any advantages over simply using the one-shot RGB data.

One possibility for LRGB with color cameras is to collect your luminance with a conventional B&W astronomical camera, and then use a one-shot camera like a DSLR for your color, which you can then combine using conventional LRGB techniques.
Chris

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Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com