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AssigneeBell Telephone Laboratories, Incorporated
InventorBarin Geoffry Haskell
Estimating the term…
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.
In a conditional replenishment video encoder wherein only selected samples are transmitted to a receiving location and each selected sample is located by a corresponding address word which represents by its value the position of the selected sample in a video line, apparatus for maintaining line synchronization comprising means for counting the number of sequential video lines wherein no samples have been selected for transmisison, means for detecting a first sample in a video line to be selected for transmission, means for coupling the address word corresponding to said selected sample to a transmission medium, and means responsive to said detecting means for coupling a bit sequence to said transmission medium in bit positions following said address word, the number of bits in said sequence being determined by a value provided at an output of said counter means.
A redundancy reduction encoder for use with a video signal having frame intervals and line subintervals comprising means for developing samples of said video signal, means for generating an address word for each of said samples to indicate by it value the position of the corresponding sample within a line subinterval, means for comparing each sample with a previously stored value in order to generate a transmit signal when the compared sample is selected for transmission, means responsive to said transmit signal for coupling to a transmission medium an amplitude word corresponding to said sample preceded by the address word corresponding to said sample, means for storing an address word corresponding to a previously selected sample, means for comparing an address word of a selected sample with the address word stored in said means for storing, and means responsive to said comparison means for transmitting a special sync word in the bit spaces preceding said address word of a selected sample when a predetermined relationship exists between the compared address word and the stored address word.
A redundancy reduction encoder for use with video signals having frame intervals and line subintervals comprising means for developing amplitude samples of said video signals, means for generating an address word for each amplitude sample which indicates by its value the position of its corresponding amplitude sample within the line subinterval, means for comparing each amplitude sample with a previously stored value in order to generate a transmit signal when the compared sample is selected for transmission to a receiving location, means responsive to said transmit signal for coupling a selected amplitude sample and its corresponding address word to a transmission channel, counter means responsive to the termination of each of said line subintervals and to the generation of transmit signals from said comparison means for counting the number of line subintervals in which no samples are selected for transmission, means for indicating the selection of a first amplitude sample in a line subinterval, and means responsive to an output from said indicating means for coupling a bit sequence to said transmission medium in bit spaces following the address word corresponding to said first amplitude sample, the number of bits in said sequence being a function of the value developed by said counter means.
Dependencies are inferred from the claim text.