Conditioning contexts for the arithmetic coding of bit planes

The arithmetic coding of the bit planes of an image represented either in the conventional weighted binary form or by the Gray code, is investigated. Two-dimensional contexts based on the pixels from the current bit plane and three-dimensional contexts on pixels from both the current and previous bit planes are studied. Results indicate that for binary bit planes, a three-dimensional template results in a significant bit rate reduction compared to a two-dimensional template of the same size. The savings are much less for Gray encoded bit planes; since the final bit rates are similar to the binary case, the need for Gray encoding is eliminated. The effect of the order of encoding the bit planes are also studied. Comparisons to conventional lossless schemes, such as predictive coding followed by Huffman or arithmetic coding, are presented