A multi-purpose VLSI chip for adaptive data compression of bilevel images

A VLSI chip for data compression has been implemented based on a general-purpose adaptive binary arithmetic coding (ABAC) architecture. This architecture permits the reuse of adapter and arithmetic coder logic in a universal way, which together with application-specific model logic can create a variety of powerful compression systems. The specific version of the adapter/coder used herein is the “Q-Coder,” described in various companion papers. The hardware implementation is in a single HCMOS chip, to maximize speed and minimize cost. The primary purpose of the chip is to provide superior data compression performance for bilevel image data by using conditional binary source models together with adaptive arithmetic coding. The coding scheme implemented is called the Adaptive Bilevel Image Compression (ABIC) algorithm. On business documents, it consistently outperforms such nonadaptive algorithms as the CCITT Group 4 (T.6) Standard and comes into its own when adapting to documents scanned at different resolutions or which include significantly different data such as digital halftones. The multi-purpose nature of the chip allows access to internal partition combinations such as the “Q” adapter/coder, which in combination with external logic can be used to realize hardware for other compression applications. On-chip memory limitations can also be overcome by the addition of external memory in special cases. Other options include the uploading and downloading of adaptive statistics and choices to encode or decode, with or without adaptation of these statistics.