LRGB combination

Invocation: nightlight -out lrgb.fits lrgb lum.fits red.fits green.fits blue.fits with appropriate filenames for your channels and desired output. You can do HaRGB by providing a H-alpha file as the first argument instead of a luminance file.

Phases and steps almost identical to RGB combination. Key differences:

• Need four input files: L, R, G, B
• Luminance always used as the refrence frame
• Color combination first done for RGB. Then converted to CIE LCH. Luminance channel replaced with L, conserving chroma/saturation and hue information