System for formatting digital signals to be transmitted

Details System for formatting digital signals to be transmitted System for formatting digital signals to be transmitted

1987-06-01

1988-03-01

Britton, Howard W.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358140, 375 31, H04N 713

Patent

active

047290200

ABSTRACT:
In a preferred embodiment, a computer is employed to control the system. The system initially accepts analog signals and converts them into digital signals, which are then compressed, at a DPCM encoder, into a three bit code. Thereafter the once compressed signals are further compressed in accordance with a variable length code. The twice compressed digital signals are transmitted through formatter circuitry whereat a tag is added to indicate (in addition to other information) what forms of compression have been employed on the digital signals which follow the tag. The twice compressed and tagged digital signals are forwarded to a buffer storage device. The role of the buffer storage is to keep a relatively constant supply of data signals so that there is a relatively constant supply of pels moving to the transmitter at a constant frequency. The computer monitors the buffer fullness and the rate at which it is being loaded or is emptying. In response to such monitoring the system compresses more lines of digitized video or compresses less lines of digitized video. Additional compression can be effected by horizontal subsampling or by changing the first DPCM coding operation from a three bit code to a two bit code. The present system also includes a decoding loop which accepts the compressed and tagged digital signals. The compressed signals are initially synchronized in response to the tags so that the compressed signals are properly advanced into the stages of the decoding loop. The compressed signals are then decompressed (decoded) in accordance with the information carried by the tag. Thereafter the expanded digital signals are converted into analog signals for display on a video screen.

REFERENCES:
patent: 4394774 (1983-07-01), Widergren
patent: 4454593 (1984-06-01), Fleming
patent: 4517596 (1985-05-01), Suzuki
patent: 4654695 (1987-03-01), Fling
patent: 4694336 (1987-09-01), Keesen

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