Data dependencies in CABAC make it difficult to parallelize and thus limits its throughput. The majority of the bins processed by the CABAC are used to represent the prediction error/residual in terms of quantized transform coefficients. This paper provides an overview of the various improvements to context selection and scans in transform coefficient coding that enable HEVC to potentially achieve higher throughput relative to AVC/H.264. Specifically, it describes changes that remove data dependencies in significance map and coefficient level coding. Proposed and adopted techniques up to HM-4.0 are discussed. This work illustrates that accounting for implementation cost when designing video coding algorithms can result in a design that can enable higher processing speed and reduce hardware cost, while still delivering high coding efficiency.
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