Color television window expansion and overscan correction for high-resolution raster graphics displays

摘要

A video pixel presentation rate expansion circuit is provided for use with a high-resolution display system. The overall display system includes a high-reso­lution monitor, a computer for providing control signals, including a high-resolution frame buffer for storing computer graphics and TV video images and reading out said video data at a rate controlled by said control signals and providing said data with a high-resolution monitor for display. The expansion circuit of the present invention comprises means responsive to an expansion pattern generated by the computer for changing the time base of the video pixel data read out of said frame buffer. Circuit includes means responsive to said expansion pattern for selective­ly repeating predetermined scan lines of said video display and for selectively repeating certain pixel along a given scan line to match the time base of the video data read out of said frame buffer to the time base of said high-resolution monitor.;According to a preferred embodiment of the invention the expansion circuit functions to modify the controi signals which controls the read-out of the frame buffer in a predetermined fashion without any additional video buffer storage means. In the simplest form of the invention the additional circuitry required comprises only two registers for holding the generated expansion patterns in the horizontal and vertical direction and two shift registers for receiving these patterns and processing same to alter the frame buffer clocks to achieve replication of predetermined lines and pixels as determined from the said expansion pattern.