Method and system for the compression and decompression of digital television signals encoded in the palplus system

摘要

This invention relates to a method and system for compressing and decompressing digital television signals encoded in the PALplus system. A PALplus encoded television signal has video signals which have an aspect ratio of 16:9 compared to an aspect ratio of 4:3 in common use for standard PAL signals. To achieve this the picture height of the main video signal is reduced from 576 active lines to 430 active lines and the remaining 144 lines are used to transmit a low-level helper signal.;If a PALplus signal is to be transmitted through a digital video compression system using a standard PAL decoder, compression artefacts in the helper signal are amplified in the PALplus receiver to such an extent that the picture is severely degraded. To avoid the need and expense of a full PALplus encoder at the output of the compression decoder, the presence of the helper signal is detected by a line counter (27) and the helper signal is switched (26) into the channel used for the luminance signal whenever the presence of the helper signal is indicated by the line counter (27). The helper signal is thus separated from the main video signal. By this means a standard PAL compression decoder can be used while avoiding the severe picture degradation referred to which would accompany transmission of the helper signal through the main video signal channel.