Telegraphy – Systems – Simplex-reversing periodic
Patent
1975-04-25
1976-06-08
Britton, Howard W.
Telegraphy
Systems
Simplex-reversing periodic
178DIG3, 179 1555R, 325 38B, H04N 712
Patent
active
039625354
ABSTRACT:
A video sample is selected for transmission only if it differs significantly in amplitude from the sample corresponding to the same spatial point in a previous video frame. An address word which indicates by its value the position of a sample within a video line is transmitted prior to the amplitude of a sample only if the previous sample was not selected for transmission. The amplitudes for selected samples are transmitted in groups preceded by an address word and terminated by a flag word. Frame synchronization is maintained by transmitting a first sync word during the vertical blanking interval. Ordinarily, the first sample in a video line selected for transmission has an address which is lower in value than the address word of the previous sample selected for transmission and, therefore, no line synchronization is necessary. The number of video lines in which no samples are selected for transmission is determined by a counting circuit and this number is transmitted in the form of a sequence of bits following the address word of the first sample selected for transmission in a video line. A second sync word is selected for transmission during the horizontal blanking interval when the counter reaches a predetermined value. To account for those rare instances when the address word of the first selected sample in a video line is higher in value than the address word of the preceding selected sample, a third sync word is transmitted prior to the address word of the first selected sample. In video-telephone systems line synchronization is thus achieved at a cost of slightly more than one bit per video line.
REFERENCES:
patent: 3347981 (1967-10-01), Kagan
patent: 3378641 (1968-04-01), Varsos
patent: 3553361 (1971-01-01), Mounts
patent: 3553362 (1971-01-01), Mounts
patent: 3571505 (1971-03-01), Mounts
Bell Telephone Laboratories Incorporated
Britton Howard W.
Dubosky Daniel D.
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