A light-diffusion member includes a substrate having light transparency, a plurality of light-diffusion parts formed on one surface of the substrate, and a light-absorbing layer formed in a region other than a region where the light-diffusion parts are formed, among the one surface of the substrate. A plurality of rubber gripping pads are included along the outward-facing surface of the annular groove for enhancing attachment of the cover to a wheel rim. A mode decision processor is provided for selecting macroblocks of the picture for GMC coding.