DEVICE FOR THE DPCM CODING OF TELEVISION SIGNALS

摘要

A DPCM coder, in which estimated values (@) are in each case subtracted from digitised picture element signals (s) and the estimated errors, after quantisation and coding, are used for signal transmission. Each estimated value (@) is derived from a reconstructed picture element signal formed in an adder (8). A limiter reducing the computing speed between the first adder (8) and the subtracter (2) can be removed from the time-critical path in that the limiter function is distributed over two parallel computing paths. On one path, the signal picked up at the adder output is subtracted and on the other path, the upper or lower limit value ( alpha .G<->, alpha .G<+>) weighted with alpha and connected through via a change-over switch (23) is in each case subtracted from the input-end picture element signal (s). An overflow detection device (26) and a multiplexer (24) ensure that of the two differences formed to this extent in each case only the difference taking into account the actual addition result (no overflow, positive overflow, negative overflow) is connected through to the quantiser (4).