A spectral encoding/decoding method, called LabRGB, was proposed last year [1]. LabRGB consists of six unique base functions and physically meaningful encoding values. LabRGB has several features; color characteristics can be estimated by its encoding values, fixed base functions need not exchange beforehand and tri-chromatic images as well as multi-spectral images can be handled by a single form. In this paper, the derivation of LabRGB was described in detail including fast straightforward calculation of encoding/decoding calculation. Then LabRGB was applied to real multi-spectral images. LabRGB performed well in encoding/decoding various types of multi-spectral images and confirmed to be suitable for practical use.