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Latest question:
How do you think the new GigE standards will influence the machine vision industry?
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High-definition (HD) video is about to arrive in a big way, as you can see by walking through any appliance store, where big signs announce that new TV sets are HDTV-ready or HDTV-compatible. With the lure of wider screens and higher resolutions fueling demand, and the supporting technology in place or being deployed, it is time for video system designers to investigate fully the issues of implementing HD. The market is getting ready for HD products, but are you as a designer HD-ready?

The Extent of HD

The first thing to acknowledge is that not all digital TV (DTV) is HDTV, and not all HD video is TV. There are standard-definition (SD) formats that digitally approximate traditional analog TV images, and low-definition (LD) formats for handheld screens and windowed images, as well as several HD formats for large screens. The right display for a given digital video application may not be the 1080i60 (1920×1080 at 60 interlaced fields per second) format that North American broadcasters are generally deploying for HDTV. This format, with its 16:9 wide-screen aspect ratio replacing the traditional 4:3, looks wonderful on a 40-inch screen or larger. But on a small screen for, say, viewing in the back seat of a car, it is difficult to see any difference in quality between HD and SD.

And HDTV is only the beginning, or perhaps it would be better to say, it is only an important application for HD, which includes a variety of applications for stored, streaming and live video, as well as broadcast television. Videoconferencing may find an HD format such as 720p30 (1280×720 at 30 progressive frames per second) satisfactory, while the same resolution with twice the frame rate (720p60) may provide the best solution for fast motion and non-stop action of sportscasts. Other formats may be more desirable for other types of applications or for viewing on unconventional displays such as wide computer monitors.

More Than Meets the Eye

Other factors besides display are involved, too. HD products generally package surround sound along with a high-resolution display, and designers should not ignore the advantages of advanced audio. Great sound can make a so-so image seem better, while the effect of a great image is diminished by inadequate sound. The system’s audio requirements are at least as important as its video requirements.

Digital video systems have to process not only the display output, but also the compressed signal input. Video compression/decompression (codec) algorithms are almost always lossy, meaning that the decompressed image is less well defined than the uncompressed original. Pushing compression beyond the ~60:1 ratio normally supported by the Main Profile of H.264/MPEG-4 AVC risks revealing flaws in the image that show up much better on HD displays. With excessively high levels of compression, it may be better to choose a smaller display and lower-resolution format.