Backward Coding of Wavelet Trees with Fine-grained Bitrate Control

Backward Coding of Wavelet Trees (BCWT) is an extremely fast wavelet-tree-based image coding algorithm. Utilizing a unique backward coding algorithm, BCWT also provides a rich set of features such as resolution-scalability, extremely low memory usage, and extremely low complexity. However, BCWT in its original form inherits one drawback also existing in most non-bitplane codecs, namely coarse bitrate control. In this paper, two solutions for improving the bitrate controllability of BCWT are presented. The first solution is based on dual minimum quantization levels, allowing BCWT to achieve fine-grained bitrates with quality-index as a controlling parameter; the second solution is based on both dual minimum quantization levels and a coding histogram, providing the ability to use target bitrate as the controlling parameter with only a small speed penalty.