Importance

Loading Importance Indicators...

Abstract

A scan converter receives VGA or SVGA graphics data and outputs NTSC or PAL TV data. The scan converter is integrated inside a personal computer's graphics controller, allowing the digital-to-analog converter (DAC) to be used for either CRT-pixel conversion or TV encoding. The VGA timing is altered to better match with TV scan-conversion. The horizontal rate is not constant but can be increased or decreased during the vertical blanking period. A second register is provided for the total number of pixels in a line during vertical blanking, while a first register contains the total number of pixels in a displayable line not during the vertical blanking period. Since lines with fewer pixels require less time to display, the period of time or rate for blanked lines is changed. An extra horizontal line is added during vertical blanking for every second frame for SVGA conversion to better match the asymmetry of TV standards. While CRT's cannot accept the variable line rate, flat-panel displays can operate properly even when the horizontal rate varies. Thus an image can simultaneously be displayed on both an external TV and on a portable computer's flat-panel display.

Loading the Abstract Image...

First Claim