Image encoding and decoding methods based on comparison of current prediction modes with reference prediction modes

摘要

Methods and devices are disclosed for encoding or decoding mode information representing a prediction mode for a current image portion by an intra mode coding process, the mode being one of plural prediction modes. In one aspect, the current image portion prediction mode value to be encoded is compared S1003 with reference (e.g., most probable mode (MPM) or a planar mode) prediction mode values derived from prediction modes of respective image portions to determine (select) from plural encoding processes; if the current mode value is different from reference prediction mode values, the current image portion prediction mode value is compared S1004 with a further predefined prediction mode value, e.g. horizontal, vertical or DC prediction mode. In another aspect the method includes deriving a first reference prediction mode based on the prediction mode value of a single or at least two reference image portion(s). Alternatively, the mode information is represented by an angular index of the angular direction of the current prediction mode; where the current angular index value is different to reference angular indexes, the angular index value of the current image portion is coded. Codeword flags may be used.