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 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, and a modulator then converts the ternary codes into a frequency and phase modulated passband signal. To recover the video signal from the passband signal, the process is reversed.
Claims7
In a limited bandwidth raster scanned imaging system including run length encoding means for converting a binary video signal having a raster scan format into binary black and white message codes, the improvement comprising
- ternary encoding means for selectively level shifting said binary message codes to provide a series of ternary black and white run length message codes having one polarity corresponding to initial bits of black message codes, another polarity corresponding to initial bits of white message codes, and a reference level corresponding to other bits of black and white run length message codes;
- and
- modulating means for supplying a passband signal which is frequency and phase modulated in accordance with said ternary codes.
In 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 including a transmitting terminal, a receiving terminal, and a limited bandwidth communications channel for interconnecting said transmitting and receiving terminals;
- said transmitting terminal having run length encoding means for converting a binary video signal into binary black and white run length message codes;
- the improvement comprising
- ternary encoding means within said transmitting terminal for selectively level shifting said black and white message codes and for interleaving said message codes on a scan line-by-scan 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,
- modulating means within said transmitting terminal for phase and frequency modulating a passband signal in accordance with said ternary message codes to provide a passband signal for transmitting said ternary codes to said receiving terminal via said communications channel, and
- decoding means within said receiving terminal for recovering said video signal from said passband signal.
A method for converting a binary video signal having a raster scan format and including picture elements representing background areas and image areas into a data compressed passband signal, 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,
- selectively level shifting 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,
- phase and frequency modulating carrier signals in accordance with said ternary codes to provide a passband signal of one frequency but opposite phases in response to bits of one logic level from black and white message codes and of a different frequency in response to bits of an opposite logic level from said black and white message codes.
Dependencies are inferred from the claim text.