TV GRAPHICS AND MIXING CONTROL

摘要

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 decoder (27) supplied with the encoded video signal, and a plurality of transmission ga (31-36) responsive to logic control signals derived from the outputs of the decoder (27). The gates (31-36) are coupled to inputs of video output stages (16) in the receiver, and operate in response to the control signals for interrupting normal video signals to the video output stages (16) and for enabling a voltage representative of a graphics display intensity level to be coupled to the video output stages (16) when graphics information is to be displayed. The system also includes a graphics level control network (25). The level control network (25) limits excessive graphics representative beam current levels to prevent image defocusing and kinescope screen burn. The level control network (25) 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.