As an extension of H.264/AVC, MVC also employs the RD optimization technique24 to select the optimal MB mode with the minimum RD cost, among candidate inter- or intramodes, and RD cost of each mode includes rate portion and distortion portion. Both inter and intramodes include different size modes, which have distinct characteristics of rate portion and distortion portion. By providing more precise motion/disparity estimation, small-size intermodes which include , , and can obtain less distortion portions of RD costs than large-size intermodes (Skip/Direct, ). However, because small-size intermodes need more bits for encoding motion vector of each partition block, they have larger rate portions of RD costs than that of large-size intermodes. For MBs with complex motion/disparity, small-size intermodes can obtain a much less distortion portion of RD cost than large-size intermodes, and they are more likely to be selected as the optimal MB mode. For MBs with smooth motion/disparity, large-size intermodes usually can provide the same level performance of distortion portions as small-size modes, and they have less rate portions than small-size intermodes due to encoding only partition information. Similar to intermodes, small-size intramodes ( and ) can also obtain less distortion portions and more rate portions than that of large-size intramode (). For MBs with complex textures, small-size intramodes will often have less RD costs than large-size intramode. For MBs with smooth texture, large-size intramode usually obtains less RD cost than small-size intramode. In this article, according to the RD properties of different size modes, all intermodes and intramodes are classified into the large-size mode (includes Skip/Direct, , and modes) and the small-size mode (includes , , , , and modes).