Adaptive runlength coding

Runlength coding is the standard coding technique for block transform-based image/video compression. A block of quantized transform coefficients is first represented as a sequence of RUN/LEVEL pairs that are then entropy coded-RUN being the number of consecutive zeros and LEVEL being the value of the following nonzero coefficient. We point out the inefficiency of conventional runlength coding and introduce a novel adaptive runlength (ARL) coding scheme that encodes RUN and LEVEL separately using adaptive binary arithmetic coding and simple context modeling. We aim to maximize compression efficiency by adaptively exploiting the characteristics of block transform coefficients and the dependency between RUN and LEVEL. Coding results show that with the same level of complexity, the proposed ARL coding algorithm outperforms the conventional runlength coding scheme by a large margin in the rate-distortion sense.