From LOCO-I to the JPEG-LS Standard

lossless image compression, standards 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 compression of continuous-tone images, JPEG-LS. The algorithm, presented at DCC'96, was conceived as a “low complexity projection” of the universal context modeling paradigm, matching its modeling unit to a simple coding unit based on Golomb codes. The JPEG-LS standard evolved after successive refinements of the core algorithm. This evolution, and the main algorithmic components of JPEG-LS are described in this paper. JPEG-LS attains compression ratios similar or superior to those obtained with state-of-the-art schemes based on arithmetic coding. Moreover, it is within a few percentage points of the best available compression ratios, at a complexity level estimated at an order of magnitude lower.