Line doubler brings video to displays
Displaying interlaced video on computer-based systems has always posed a problem for systems integrators. NTSC displays frames of 525 lines composed of even and odd fields, each of which is displayed 60 times per second. This interlacing can cause image artifacts such as moiré patterns to appear on the display. And NTSC (or RS-170) and PAL formats are incompatible with today`s computer-based displays, where RGB images of 1280 ¥ 1024 ¥ 24 bits may be displayed noninterlaced at 72-Hz refresh rates. That is why many imaging systems require two monitors--one to display image graphics and one for computer graphics.
To combine RS-170 images on computer screens requires deinterlacing or line-doubling the video signal. Several methods are currently available to accomplish this, including field merging, line replication, and vertical and temporal filtering. While both field merging and line replication introduce image artifacts, performing temporal filtering between fields and vertical filtering within a field can reduce motion and aliasing effects. This method forms the basis of the gmVLD8 8-bit and gmVLD10 10-bit line-doubler ICs from Genesis Microchip (Markham, Ontario, Canada).
In operation, the gmVLD8 IC accepts 16-bit interlaced 4:2:2 YUV or 24-bit RGB and outputs 16-bit 4:2:2 YUV or 24-bit noninterlaced output. Output from the device is equal to the input video field rate. Both three-field and two-field processing and static operating modes can be accomplished using the device. Three-field and two-field modes perform temporal and vertical filtering and are designed for motion video sequences. The static (field-merging) mode is designed to process video with very little motion content.
Feral Industries (Overland Park, KS), Chisolm (Campbell, CA), and Electrohome (Kitchener, Ontario, Canada) have already integrated the gmVLD into their products. Feral Industries has designed the device into its $3495 LD-2000 line-doubler system that features a built-in TBC, freeze-function, routing switcher, and RS-232 interface. "The gmVLD8 easily interfaces to memory," reports Bob Bachus, a systems designer with Feral.
Chisolm and Electrohome have used the device in their range of projection systems. Like other Chisholm projectors, the Aurora allows live video to be combined with computer-based images. In its new Aurora color projector, Chisolm uses Genesis` gm833x3F digital scaling engine and the gmVLD8 line doubler. "Users expect the picture to fill the screen regardless of source," says Jim Molenda, Chilsolm`s vice president of product development. Like Chisolm, Electrohome has also previewed a projector--the Marquee series--using the device. "The device eliminates many of the artifacts visible with standard line-doubling technologies," claims Tom Kapucija, Electrohome`s product manager for accessories and interfaces.