Context Clustering in Lossless Compression of Gray-Scale Image.
ABSTRACT We consider and evaluate the context clustering method for lossless image compression based on the existing LOCO-I algorithm
used in JPEG-LS — the latest lossless image compression standard. We employ the LOCO-I Medpredictor to enroll the error pixels.
The contexts are defined by calculating gradient of current pixels. The three directional gradients are quantized with different
codebook size (7, 9, 19) respectively. The error pixels are then corrected and encoded by the clustered-contexts. A main advantage
of using the context clustering method is that it can eliminate the storage of probability vector. An adaptive arithmetic
encoder is also introduced to yield a higher compression rate.