Graphics Display System with Anti-Flutter Filtering and Vertical Scaling Feature

Abstract

A graphics integrated circuit chip is used in a set-top box for controlling a television display. The graphics chip processes analog video input, digital video input, and graphics input. The chip includes a single polyphase filter that preferably provides both anti-flutter filtering and scaling of graphics. Anti-flutter filtering may help reduce display flicker due to the interlaced nature of television displays. The scaling of graphics may be used to convert the normally square pixel aspect ratio of graphics to the normally rectangular pixel aspect ratio of video.

1 . A display system comprising:
 a graphics processing system for blending a plurality of graphics images using a plurality of alpha values associated with the graphics images to generate a blended graphics image, wherein the graphics processing system also processes the graphics images and/or the blended graphics image to place the blended graphics image in a format suitable for blending with a video image;   a memory for storing the blended graphics image; and   a compositor for blending the blended graphics image with the video image using the alpha values and/or at least one value derived from the alpha values.   
     
     
         2 . The display system of  claim 1 , wherein the graphics processing system includes a polyphase filter for processing the graphics images and/or the blended graphics image. 
     
     
         3 . The display system of  claim 2 , wherein the polyphase filter is used to anti-flutter filter the graphics images and/or the blended graphics image. 
     
     
         4 . The display system of  claim 2 , wherein the polyphase filter is used to scale the graphics images and/or the blended graphics image. 
     
     
         5 . The display system of  claim 4 , wherein the polyphase filter scales the graphics images and/or the blended graphics image vertically and/or horizontally. 
     
     
         6 . The display system of  claim 2 , wherein the polyphase filter is programmable. 
     
     
         7 . The display system of  claim 2 , wherein the polyphase filter is capable of operating in a field mode wherein every other line of the graphics images and/or the blended graphics image is processed during filtering. 
     
     
         8 . The display system of  claim 2 , wherein the polyphase filter is capable of operating in a frame mode wherein every line of the graphics images and/or the blended graphics image is processed during filtering. 
     
     
         9 . The display system of  claim 6 , further comprising a second memory for storing at least one of horizontal coefficients and vertical coefficients for programming the polyphase filter. 
     
     
         10 . A method of generating a display image using a plurality of graphics images and a video image, comprising:
 blending the plurality of graphics images using a plurality of alpha values associated with the graphics images to generate a blended graphics image, wherein the graphics images and/or the blended graphics image is processed to place the blended graphics image in a format suitable for blending with the video image;   storing the blended graphics image in a memory; and   blending the blended graphics image with the video image using the alpha values and/or at least one value derived from the alpha values to generate the display image.   
     
     
         11 . The method of  claim 10 , wherein the graphics images and/or the blended graphics image is scaled in vertical and/or horizontal directions. 
     
     
         12 . The method of  claim 11 , further comprising programming a polyphase filter with vertical and/or horizontal coefficients to perform scaling in the vertical and/or horizontal directions. 
     
     
         13 . The method of  claim 12 , wherein the vertical and/or horizontal coefficients are used to also perform anti-flutter filtering. 
     
     
         14 . The method of  claim 10 , wherein the graphics images and/or the blended graphics image is anti-flutter filtered.