HIGH CAPACITY COMPRESSED DOCUMENT IMAGE STORAGE FOR DIGITAL COLOR PRINTERS

摘要

A high capacity compressed document image storage apparatus for color printing systems. The compressed document storage system is composed of the following major components: 1) An image creation system which can operate on a band-by-band basis. 2) An input memory which stores at least one band of the uncompressed page image. Two bands are preferred to allow double buffering, so that the RIP and compression stages can proceed simultaneously. 3) A page image compression system which can operate on a band-by-band basis. A new page image compression scheme which achieves high compression ratio and preserves high image quality is disclosed. 4) A mass storage device for storing compressed page images. 5) A real-time page image expansion system which expands the compressed page images at the rate required by the print engine. 6) An output memory which stores at least one band of the expanded page image. The recommended minimum is the number of lines from the first line of the print engine to the last line of the print engine, plus two bands. 7) An interface which reads data from the output memory and provides it at the correct timing to the print engine. An improvement to JPEG image compression when used with text or graphics overlays is also disclosed.