Reduced memory graphics-to-raster scan converter

An all-raster scanned video system comprising:

• means for providing a composite video signal having analog information and horizontal/vertical sync signals;
• means responsive to said composite video for providing an output of said horizontal/vertical sync signals;
• means for providing data to be superimposed on the video signal of a raster-scanned video display;
• means for receiving said data and responsive to the outputs of said horizontal/vertical sync signals for providing and updating successive outputs of data representing the data to be displayed on fractional parts of a raster field;
• first memory means for storing data from said outputs of data representing a fractional part of a raster field;
• second memory means for storing data from said outputs of data representing a successive fractional part of a raster field;
• means responsive to the outputs of said horizontal/vertical sync signals to cause alternate outputs of said data stored in said first and second memory means;
• and
• multiplexer means for alternately receiving the output of one of said memory means representing data from a fractional part of said raster scan while data for a successive fractional part of said raster scan is being stored in the other of said memory means and combining that output with the video signal for superimposing the data on the video signal.

A method for superimposing data on the analog video of an all-raster scanned video system comprising:

• providing an analog video signal;
• storing data representing a fraction of the raster field on which data is to be superimposed;
• storing data representing a successive fraction of the raster field on which data is to be superimposed;
• and
• alternately and successively combining the stored data representing fractional fields with said analog video signal to form successive raster fields and successive frames of a video display having superimposed data.