Abstract: A method and apparatus are described for modifying an analogue video signal to impair its conversion to a digital signal by an analogue to digital converter. The resulting modified signal may prevent the operation of the analogue to digital converter altogether, or even if a digital signal can be output and recorded, may result in a signal which is difficult to view due to a reduction in quality on playback. The modifications made to the signal include altering the amplitude of the horizontal synchronization pulses in the original signal, and/or modifying the level of the back porch, or the region of the signal adjacent the back porch. Additionally, methods are contemplated for the use of specific response models for target analogue to digital converters, and display devices.

Abstract: An apparatus and method for applying anti-copy protection to a raster-scanned video signal are described. A square waveform 52 is added to the vertical synchronization 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.

Abstract: A copy protection method and apparatus is disclosed. Various protection signals are added to a video signal in the vicinity of the color burst part of the signal. The protection signals are selected to interfere with the frequency down conversion process in the video recorder so that the color burst cannot be recorded properly. The protection signals are chosen so that when a modified video signal containing the original video signal and the protection signals has been recorded by a video recorder, playback of the modified video signal exhibits visual artefacts that are not visible before recording of the modified signal occurred. The protection signals are also used to carry digital control information for controlling the operation of a digital recorder.