| 摘要 |
Time-varying picture signals of a plurality of channels are predictively coded by utilizing the interframe correlation and multiplexed at the transmitting side. The signals are separated for each channel, switched and selected for any channel for decoding at the receiving side after transmitted. When the receiving channel is switched over to other channel, a decoding error can occur and a reproduced screen can collapse since the predicting signals do not coincide with each other at the transmitting and receiving sides. Therefore, when the plurality of channels is selectively switched for decoding by using a single decoder, the refresh is repeated at predetermined time intervals in a short period of time by utilizing the intraframe correlation when the coding is carried out at the transmitting side so that, even if the channel is switched, an excellent reproduced screen may be immediately obtained. However, during the refresh, the compression ratio is reduced compared with that of the bit rate when a normal interframe correlation is carried out. Therefore, when the refresh is carried out, the amount of transmitted information for part or all of the channels other than the refreshed channel is compressed and, conversely, the amount of transmitted information for the refreshed channel is increased by the compressed amount and allocated. Thus, even if the channel is switched at the receiving side, the decoded image for the newly selected channel can be promptly reproduced.
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