A block is called as an all-zero block (AZB) if all its transformation coefficients are quantized to be zero. Provided that an AZB can be detected early, the processes of transformation and quantization on an AZB can be omitted. This leads to significant redundant computations being skipped and thus speeds up the coding of a video sequence. In this paper, a more precise threshold value than previous methods is proposed to increase the number of AZBs detected. The threshold value is cautiously derived from relative theories and no assumption is adopted, ensuring that video quality is not degraded. A comparison to different methods on detectable ranges is graphically illustrated to show the improvement of the proposed method. The computational complexity of the proposed algorithm is analyzed. Experimental results show that the proposed algorithm outperforms the previous methods in all cases and achieves major improvement of computation reduction in the range from 4% to 71.3% compared to previous methods. The larger the quantization is, the larger the computation reduction is.
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