The LOCO-I lossless image compression algorithm: Principles and standardization into JPEG-LS

LOCO-I (LOw COmplexity LOssless COmpression for Images) is the algorithm at the core of the new ISO/ITU standard for lossless and near-lossless compre ssion of continuous-tone images, JPEG-LS. It is conceived as a "low complex ity projection" of the universal context modeling paradigm, matching its mo deling unit to a simple coding unit. By combining simplicity with the compr ession potential of context models, the algorithm "enjoys the best of both worlds," It is based on a simple fixed context model, which approaches the capability of the more complex universal techniques for capturing high-orde r dependencies. The model is tuned for efficient performance in conjunction with an extended family of Golomb-type codes, which are adaptively chosen, and an embedded alphabet extension for coding of low-entropy image regions . LOGO-I attains compression ratios similar or superior to those obtained w ith state-of-the-art schemes based on arithmetic coding, Moreover, it is wi thin a few percentage points of the best available compression ratios, at a much lower complexity level. We discuss the principles underlying the desi gn of LOGO-I, and its standardization into JPEG-LS.