| 摘要 |
An apparatus and method for applying anti-copy protection to a raster- scanned video signal are described. In a first aspect, a square waveform (52) is added to the vertical synchronisation pulses (50) of the video signal. The effect of the waveform is not apparent until it has been recorded by a video cassette recorder. The anti-copy protected video signal can therefore be viewed normally on a display device at or near to the picture quality intended by the originator of the video signal, but once recorded, exhibits a reduction in picture quality which makes the video signal quite unattractive to view. In a second aspect, a positive-going pulse (94) is added to the back porch of the raster-scanned video signal such that it is substantially contiguous with the negative-going horizontal synchronisation pulse (86). The effect of the pulse is again apparent following recording of the video signal by a video cassette recorder. A negative-going pulse (96) may be added after the color burst (92) and a further positive-going pulse (98) at the start of the active line (84). |
