HEVC编码技术概览.ppt

3、Inter Prediction 3.1. Motion Vector Pridiction For each CU or PU, the best motion vector predictor is computed with the process specified as follows. Firstly, a set of motion vector predictor candidates shall be normative process, by referring to motion parameters of neighboring partitions. Then, the best one from the candidate set is determined by a criterion that selects a motion vector predictor candidate that minimizes the cost Jmotion. 3.1.1. Coding Mode In the HM encoder, an inter CU can be segmented into multiple inter PUs. An inter CU can be encoded with one of the following coding modes : MODE_SKIP, MODE_DIRECT, MODE_INTER, and MODE_MERGE. For MODE_SKIP, MODE_DIRECT and MODE_MERGE cases, any sub-partitioning is not allowed. On the contrary, four types of further partitioning in the CU can be allowed for MODE_INTER case. The HM encoder first evaluates CU coding costs with skip and direct mode . For these cases, motion vector predictor for the current CU is directly used as current motion vector. The motion vector to be used for MODE_SKIP or MODE_DIRECT are determined by checking all possible motion vector candidates and selecting the best one that minimizes the cost Jmode. The HM encoder compares the coding cost of MODE_SKIP and MODE_DIRECT first, takes the better mode, and then proceed to checking other remaining variations. 3.1.2. Skip/Direct mode If the coding cost Jmode is smaller than the one obtained in Skip/Direct mode, pred_mode is set to “MODE_MERGE”. In this case, motion vector of the selected left or upper partition are directly used as current motion parameters. After the process specified in the previous section, the HM encoder evaluates whether motion merging should be enabled or not for the current CU. Decision on the use of motion merging is performed only at CU level whose PU size is SIZE_2Nx2N, which is identical to CU size. The decision on the use of motion merging starts with checking availabilities of left and