LRGB stands for Luminance, Red, Green, and Blue. This is a photography technique that combines an unfiltered (or UV-IR filtered) Luminance frame - essentially a black-and-white image - with images taken through colored filters. The advantage of the LRGB technique is that it can provide a higher overall signal-to-noise ratio than simply combining three color images. It is also possible in many cases to combine a higher-resolution Luminance image with slightly lower-resolution RGB images without significant loss of image quality.