LRGB

LRGB, short for Luminance, Red, Green and Blue, is a photographic technique used in amateur astronomy for producing good quality colour photographs by combining a high-quality black-and-white image with a lower-quality colour image

In amateur astronomy, it is easier and cheaper to obtain good quality, high signal-to-noise ratio, images in black and white. The LRGB method is used to work around this to get good colour images. The colour information from the colour image is combined with the overall brightness from the black-and-white image. As only the colour information is used, the noise in the colour image is not transferred to the final image, retaining the quality of the black-and-white image.