| 摘要 |
A method of treating a video signal to allow playing on a video cassette recorder (VCR) but not to allow copying using a VCR having an automatic gain control (AGC) when recording. The method involves inserting one or more pulses (22) into the back porch (45) during the horizontal blanking interval and attenuating the last lines (24) of the picture information portion (16) and horizontal synchronisation information (18) at the end of each alternate frame. The pulses (22) comprise a pulse signal (44) inserted into the colour burst information portion (34), an opposing pulse signal (45) having a magnitude sufficient to offset the change in the dc level of the colour burst portion (34), caused by the pulse signal (44), and a further pulse (50) inserted somewhere from the last half of the remainder of the back porch (45) to the end of the start of the picture information portion (16). Consequently, the dc level of the colour burst information portion (34) is always maintained at the same level as it was prior to the insertion of the pulses (20). A particular encoder (52) is also disclosed together with a method and apparatus (101) for decoding a video signal treated in the aforementioned manner so as to recover the original video signal.
|
