LRGB quadcolor composit test

LRGB quadcolor composit method is a new technique to make high S/N color images. Also it will allows us to reduce the total exposure time.

1. Take R, G, B images and a monochrome image (without filter or with filter for example DSP filter or H-alpha filter etc).

2. Composit the RGB images in a tricolor image.

3. Load it in PhotoShop, and comvert it to Lab mode.
Note: L-ch is "brightness" channel, a/b-ch include the color signal.

4. Replace the L-ch with the monochrome image.
Note: the position of stars in both images must be adjusted before replacing.

This process is LRGB quadcolor composit process, where L means "Luminance". You do not need high quality RGB images for a/b ch, if you obtain a good monochrome image for L-ch. Therefore you may take the RGB images with 2x2 or 3x3 bining.

Also see an LRGB composit test by Al Kelly


M74 original images

Gray channel: 31cm F=5 Newtonian + HPC-1 CCD + DSP filter (80min)
RGB channel: 20cm F=4 Newtonian + ST-7 CCD + SBIG filters
(R=G=B=30min, 2x2 bining for B)

LRGB composit result for M74 by Lab method



NGC253 original images by C5

Gray channel: C5 + ST-7 Nofilter (22 min)
RGB channel: C5 + ST-7 + SBIG RGB filters + Edmund new IR block
(R=G=B=20 min, 2x2 bining)
Self guided images

LRGB composit image of NGC253 by Lab method
(proposed by myself)

LRGB composit image of NGC253 by layer method
(proposed by Robert Dalby)

Note that both results are very similar.

LRGB composit image of NGC253
by HLS mode of Picture Publisher 4.0 (MicroGrafx)

(proposed by Oohashi)

HLS mode is somewhat senstive to tone-curve tuning of RGB image.


The color images are processed by
Digital development and color enhancement method.


If you are interested in my C5 mobile imaging system,
please go to C5 image gallary


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