Run length encoding and decoding methods and means
AssigneeXerox Corporation
InventorEiichiro Furuta
Life of this patent
Estimating the term…
Abstract
Black and white run length encoding means first convert a binary video input signal having a raster scan format into binary black and white run length message codes which are preselected so that the initial or lead bit of each of those codes is at a given logic level. Ternary encoding means then convert the binary message codes into a series of ternary black and white run length message codes which have distinctive amplitude transitions at any intra-scan line code boundaries. To recover the video signal, the process is reversed. Moreover, a passband signal for transmitting the ternary codes from a transmitting terminal to a receiving terminal via a limited bandwidth communications channel may be provided by amplitude modulating a carrier frequency signal in accordance with the ternary codes.
Claims7
A data compressor for compressing a binary video signal having a raster scan format, said video signal having one logic level for background representing picture elements and an opposite logic level for image representing picture elements;
- said compressor comprising the combination of
- white run length encoding means for converting runs of said video signal at said one logic level into binary white run length message codes,
- black run length encoding means for converting runs of said video signal at said opposite logic level into binary black run length message codes, and
- ternary encoding means for alternatively responding to the binary white and black message codes from each scan line of said video signal and for selectively level shifting bits of said message codes to provide a series of ternary black and white run length message codes having intra-scan line code boundaries marked by distinctive amplitude transitions.
A facsimile system for providing a facsimile copy of a subject copy in response to a binary video signal having a raster scan format;
- said system comprising a transmitting terminal, a receiving terminal, and a limited bandwidth communications channel for interconnecting said transmitting and receiving terminals;
- said transmitting terminal including
- white run length encoding means for converting runs of background representing picture elements within said video signal into binary white run length message codes,
- black run length encoding means for converting runs of image representing picture elements within said video signal into binary black run length message codes,
- ternary encoding means for selectively level shifting bits of said black and white message codes and for interleaving said message codes on a scan line-by-scan line basis to provide a series of ternary black and white run length message codes having any intra-scan line code boundaries marked by distinctive amplitude transitions, and
- modulating means for amplitude modulating a carrier signal in accordance with said ternary message codes to provide a passband signal for transmission to said receiving terminal via said communications channel;
- and
- said receiving terminal including
- demodulating means for recovering said ternary codes from said passband signal,
- ternary decoding means for recovering said binary black and white run length message codes from the recovered ternary codes,
- run length decoding means for reconstructing said binary video signal in response to the recovered binary black and white run length message codes, and
- means for printing said facsimile copy in response to the reconstructed video signal.
A method for compressing a binary video signal having a raster scan format and including picture elements representing background areas and image areas, said method comprising the steps of
- converting runs of background representing picture elements within said video signal into binary white run length message codes,
- converting runs of image representing picture elements within said video signal into binary black run length message codes,
- interleaving said white and black run length message codes on a scan line-by-scan line basis, starting with a white run length message code for each scan line, and
- selectively level shifting bits of the interleaved white and black run length message codes to provide a series of ternary black and white run length message codes having distinctive amplitude transitions to identify intra-scan line code boundaries.
Dependencies are inferred from the claim text.