| 摘要 |
PCT No. PCT/GB86/00783 Sec. 371 Date Jan. 25, 1988 Sec. 102(e) Date Jan. 25, 1988 PCT Filed Dec. 19, 1986 PCT Pub. No. WO87/06418 PCT Pub. Date Oct. 22, 1987.Video signals from a source are digitized and applied to a source coder which segregates the signals into four channels (CH1 to CH4) of progressively less visual significance. CH1 carries basic picture information at a relatively low resolution. CH2 to CH4 carry differential information at progressively higher resolutions. The four channels signals are applied to respective coders and the digital outputs are combined in a matrix with voltage levels falling off as visual significance decreases. Received signals, transmitted say by way of a satellite, are applied to a first, high level decoder which extracts the digital waveform for CH1 as DCH1. This is recoded and subtracted from the input to provide a signal to a decoder which recovers CH2 as DCH2, and so on. DCH1 to DCH4 are applied to a source decoder complementary to the coder to recover the source signal. Low significant channels can be omitted at the transmitter, or not be recovered at the receiver to adapt to the prevailing signal to noise performance.
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