Constrained motion compensation for very low bit rate video compression

To achieve a higher compression ratio for very low bit rate (VLBR) video compression, motion estimation has to be more reliable and easier to code. Many segmentation based techniques try to approximate several motion vectors by a single global motion vector so that fewer vectors are required. However, a global motion vector may not be a good representation for the original vectors and the bit saving is not worth the loss. This paper proposes a new scheme for motion vector representation. Many candidates from full search block matching are selected for merging possibility. Blocks which experience similar displacement are combined to form a single object. Upon compensation for object translation or global compensation, accurate motion of each block can be identified by local compensation within an object. Instead of presenting object movement as a vector, a specific index is assigned to reduce the overhead bits. Based on extensive simulation, the proposed method with an appropriate threshold shows an improvement over standard block based hybrid schemes.