Providing an accurate tally indication of sources in use for output

An apparatus for processing digital video signals, comprising means for selectively combining picture signals from a number of sources to provide a resulting video image signal in which image information from at least one of said different sources contributes only to a selected partial area of an image frame of the resulting picture image, means for providing, in association with each of said picture signals, an accompanying tally signal identifying the source of said signal, and means for processing said tally signals to provide, in association with the combined output picture signal, an encoded tally signal identifying each source contributing to each field or frame of said output picture signal.

An apparatus for use in processing a digital video signal, comprising means for receiving a digital video signal including a first digital picture signal together with a first key signal and an encoded tally signal identifying a source of the first picture signal, means for generating a second key signal for controlling a video effect to be applied to said first digital picture signal, means for modifying said first key signal with said second key signal whereby the modified first key signal defines the presence in a second, mixed picture signal of image information derived from the first picture signal and means for modifying said tally signal with said second key signal whereby said tally signal identifies the source of said first picture signal only when image information from the latter signal is contributing to the second mixed picture signal.

An apparatus for use in processing a digital video signal, comprising means for receiving a digital video signal including an encoded tally signal, means for deriving from said tally signal a succession of digital words corresponding to pixels of the said picture signal whereby each bit in each tally word has a value which is determined by the presence or absence in said corresponding pixel of information from a given signal source, and means for combining selected tally words to form the logical OR thereof whereby the resulting single tally word serves to define all signal sources contributing to picture information contained in a corresponding group of pixels.

A method of processing a digital video signal comprising the steps of providing, in association with a picture image signal, an accompanying key signal for controlling mixing of said image signal in a subsequent processing step and an accompanying tally signal for identifying a source or sources of picture information contributing to said image signal, whereby the key signal and the tally signal are together incorporated in a signal having a colour picture signal format, comprising a luminance component and a chrominance component, with the key signal provided by the luminance component and the tally signal provided by the chrominance component.