Apparatus for converting an RGB signal into a composite video signal and its use in providing computer generated video overlays

DETAILED DESCRIPTION An improvement in an apparatus which converts RGB signals into a composite video signal is disclosed.
Notch filters are used centered at certain frequencies.
These frequencies are equal to the dot clock frequency of the RGB signal divided by integers provided that the frequency resulting from this division falls within the chroma subcarrier spectrum.
This improvement is used in an apparatus for providing video output signals containing a composite video signal merged with first RGB video overlay signals.
A keying signal generation means providing a keying signal indicating when the image represented by the video overlay signal overlies the image represented by the composite video signal.
A first converter converts the video composite signal into second RGB signals.
A second converter is used to convert the first RGB signals into a composite overlay signal using notch filters to filter the luminance signal in the conversion process.
Merging occurs in both a first and a second switch.
A first switch under control of the keying signal selects between the first and second RGB signals.
In a second switch the keying signal, filtered by notch filters, is used to select between the composite video signal and the composite overlay signal.
Other aspects of the present invention will be apparent from the detailed description of the invention.