Method and apparatus for processing pel signals of an image

Abstract

A system for processing image data of a text document in compressed form wherein pel signals of the original image are stored in pel positions in an input image buffer and the pel signals stored in every other pel (EOP) positions in the input buffer are sequentially fetched, along with respective pluralities of neighboring pel signals stored in EOP positions and compressed by adaptive arithmetic compression to generate a first set of compressed data which is stored in a memory. The pel signals stored in remaining pel (RP) positions in the input image buffer are also sequentially fetched, along with respective pluralities of neighboring pel signals, including at least one signal stored in an RP position and a plurality of signals stored in EOP positions, and compressed by adaptive arithmetic compression to generate a second set of compressed data which is stored in a memory. The first and second sets of compressed data may be decompressed to reproduce the pel signals stored at EOP positions, and the pel signals stored in RP positions along with their respective pluralities of neighboring pel signals stored in EOP positions, and stored in an output image buffer. The fetching operation includes selecting one of a plurality of sampling windows, each having a different sampling pattern, for sampling the pel signals making up the first and second sets of data during compression and decompression to achieve the improved data volumes.