Video and graphics system with square graphics pixels

Abstract

A video and graphics system provides square graphics pixels to blend images having 640×480 pixels, such as graphics images provided by some set top boxes and intended to be displayed at a 12.27 MHz display sample rate, with images having 704×480 pixels, such as ITU-R 601 compliant images such as NTSC SDTV images, having oblong pixels and displayed at a 13.5 MHz display sample rate. A sample rate converter including a multi-phase-multi-tap filter is used to generate square pixels. The multi-phase-multi-tap filter provides a good balance of sharpness, smoothness, anti-aliasing and reduced ringing. The multi-phase-multi-tap filter can also be used to convert images having 320×480 pixels to images having 704×480 pixels. The multi-tap filter can be used for scan rate conversion of graphics or video images for HDTV or SDTV applications.

1 . A video and graphics system comprising:
 a first input for receiving a graphics image comprising graphics pixels, the graphics pixels having square pixel aspect ratio;   a second input for receiving a video image comprising video pixels, the video pixels having non-square pixel aspect ratio, the video image having a larger number of pixels per scan line than the graphics image;   a sample rate converter for converting sample rate of the graphics image so that the number of graphics pixels per scan line of the graphics image becomes greater than or equal to the number of video pixels per scan line of the video image; and   a video compositor for blending the graphics image with the video image,   wherein the graphics image is scaled horizontally so that the graphics image can be overlaid on the full width of the video image, and the square pixel aspect ratio of the graphics pixels is maintained.