US 4,218,698 AGranted

TV Graphics and mixing control

AssigneeRCA Corporation

InventorsTheodor E. Bart, Ronald A. Mills

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Abstract

A system employed in a television receiver for decoding and displaying graphics information such as may be encoded on a broadcast video signal. The system includes a graphics signal decoder supplied with the encoded video signal, and a plurality of transmission gates responsive to logic control signals derived from outputs of the decoder. The gates are coupled to inputs of video output stages in the receiver, and operate in response to the control signals for interrupting normal video signals to the video output stages and for enabling a voltage representative of a graphics display intensity level to be coupled to the video output stages when graphics information is to be displayed.The system also includes a graphics level control network. The level control network limits excessive graphics representative beam current levels to prevent image defocusing and kinescope screen burn. The level control network also adjusts the graphics display intensity level in accordance with the level of image representative video signals in a mixed video plus graphics display mode, to preserve a desired contrast relationship between the displayed video and graphics information.

Claims14

Dependent claims

In a video signal processing system including a video signal processing channel, a kinescope for displaying images derived from processed video signals, and means for coupling processed video signals from said video channel to intensity control electrodes of said kinescope, apparatus comprising:

a source of signals containing graphics information to be displayed by said kinescope;
means coupled to said source of signals for deriving therefrom signals representative of graphics information to be displayed;
bias means for providing a graphics intensity bias signal representative of a desired intensity level of displayed graphics information;
first switching means having a signal input terminal coupled to said video channel, a signal output terminal coupled to said coupling means, and a switching control input terminal;
second switching means having a signal input terminal coupled to said graphics bias signal, a signal output terminal coupled to said coupling means, and a switching control input terminal;
and
control means responsive to output signals from said deriving means for providing switching control signals to said switching control input terminals of said first and second switching means, for (a) enabling said first switching means to conduct video signals to said coupling means, and disabling said second switching means to prevent conduction of said graphics bias signal to said coupling means in a normal operating mode of said system when video signals alone are to be displayed, and (b) disabling said first switching means to prevent conduction of video signals to said coupling means, and enabling said second switching means to conduct said graphics bias signal to said coupling means during graphics display intervals in a graphics display operating mode of said system.

4 more elements

In a color television receiver including a plurality of video signal paths for conducting a plurality of color image representative video signals derived from a composite television signal, said composite television signal subject to inclusion of encoded graphics information to be displayed;

a kinescope for displaying images derived from said video signals and having a plurality of intensity control electrodes;
and a video output amplifier stage having a plurality of signal inputs, for coupling said plural video signals to respective intensity control electrodes of said kinescope;
apparatus comprising:
means, including graphics signal decoding means, for decoding said television signal to derive therefrom decoded output signals representative of said graphics information to be displayed;
bias means for providing a graphics intensity bias signal representative of a desired intensity level of displayed graphics information;
a plurality of video signal switching means, each having a signal input terminal coupled to a separate one of said video signal paths, a signal output terminal coupled to a separate one of said video amplifier inputs, and a switching control input terminal;
a plurality of graphics signal switching means, each having a signal input terminal coupled to said graphics bias signal, a signal output terminal coupled to a separate one of said video amplifier stage inputs, and a switching control input terminal;
and
control means responsive to output signals from said deriving means for providing switching control signals to said switching control input terminals of said video and graphics signal switching means, for (a) enabling said plurality of video switching means to conduct video signals to said video amplifier, and disabling said plurality of graphics switching means to prevent conduction of said graphics bias signal to said video amplifier in a normal operating mode of said receiver, and (b) disabling said plurality of video switching means to prevent conduction of video signals to said video amplifier, and enabling said plurality of graphics switching means to conduct said graphics bias voltage to said video amplifier during graphics display intervals in a graphics display operating mode of said receiver.

6 more elements

Dependencies are inferred from the claim text.