Abstract: Apparatus for controlling a visual display unit from a video signal which is present for a first period of time such that an image corresponding to the signal can be displayed for one or more further such periods. The apparatus stores a digital representation of the video signal which is used to enable the required image to persist for the one or more further periods. The apparatus also generates during the first period a correction signal which is combined with the video signal and used to compensate for any imprecision in the stored signal. This arrangement permits the use of relatively small storage devices and relatively simple analogue-to-digital converters.

Abstract: A method and apparatus for modifying a color television signal permits three types of information to be coded onto a single subcarrier. Preferably two chrominance signals and a low frequency luminance signal are modulated onto the subcarrier in different sets of two such signals per scan line, such different sets being alternated on a line-by-line basis. The signals of such a set of two while occurring simultaneously are displaced in phase on the subcarrier and the subcarrier frequency is preferably selected to be an odd multiple of one-quarter of the line frequency. By so selecting the subcarrier frequency, a combination of the subcarrier signal with a luminance signal may be effected in a manner allowing for subsequent signal separation by comb filtering.