Multi-hypothesis motion-compensated prediction extends traditional
motion-compensated prediction used in video coding schemes. Known
algorithms for block-based multi-hypothesis motion-compensated
prediction are, for example, overlapped block motion compensation (OBMC) and
bidirectionally predicted frames (B-frames). This paper presents a
generalization of these algorithms in a rate-distortion framework. All
blocks which are available for prediction are called hypotheses. Further, we
explicitly distinguish between the search space and the superposition of
hypotheses. Hypotheses are selected from a search space and their
spatio-temporal positions are transmitted by means of spatio-temporal
displacement codewords. Constant predictor coefficients are used to combine
linearly hypotheses of a multi-hypothesis. The presented design algorithm
provides an estimation criterion for optimal multi-hypotheses, a rule for
optimal displacement codes, and a condition for optimal predictor
coefficients. Statistically dependent hypotheses of a multi-hypothesis are
determined by an iterative algorithm. Experimental results show that
increasing the number of hypotheses from 1 to 8 provides prediction gains up
to 3 dB in prediction error.
|