OTHER TECH

When converting to a resolution higher than that of the incoming signal - from 480p (852 x 480 pixels, horizontal by vertical, in a 16:9 frame) to 720p (1,280 x 720 pixels), for example, or either of those resolutions to 1080p (1,920 x 1,080) - a scaler has to interpolate between pixels in a frame to create new ones. It is not a simple stretching process. In fact, it usually will result in a completely new set of pixels mathematically generated from the originals. Good scalers use sophisticated alogorithms to arrive at optimum pixel values not only in the context of the current frame but also with respect to preceding and succeeding frames, so that motion is smooth and natural looking. Among the biggest challenges to a scaler is noise in the signal, such as from analog videotape or a poor-quality cable or broadcast TV transmission, which upconversion can accentuate. One of the marks of an outstanding scaler is good performance with noisy sources.

Not all scaling is upconversion, however. For example, if you send the 1080p output from an HD DVD or Blu-ray Disc player to a display with a lower resolution (720p, 1,366 x 768, 1,024 x 768, etc.), the set will have to scale the video down. This involves a sort of inverse-interpolation process known as decimation, the goal being to reduce the number of pixels while preserving as much information as possible. With more and more devices offering video scaling, including DVD players, A/V receivers and preamps, and of course HDTV sets, opportunities for yo-yo scaling - upconversion followed by downconversion followed by upconversion again - are growing. Generally speaking, it is best not to scale a video signal more than once unless absolutely necessary.

Scaling: The Bottom Line Scaling is hard to do, and bad scaling can look really, really bad (especially if it starts off with mediocre deinterlacing). Historically, good scalers have been very expensive, even if all they did was line-double 480i to 480p. And the very best standalone scalers, from companies such as Faroudja, Key Digital, Runco, Pixel Magic, and Anchor Bay, are still pricey. The good news is that the growing need for video scaling has led to substantial progress further down the food chain - a trend that will surely continue. Still, before you buy an HDTV set, cast a critical eye on how it looks with a variety of input signals. Pay special attention to what the set does with ordinary analog signals from cable or broadcast TV, which tend to give crummy scalers the biggest fits. Look particularly at what happens around the edges of moving objects. (Problems are often most apparent on slowly moving objects in the background.) Jagged or fuzzy edges or halos around objects are a bad sign (although these can also be caused by excessive compression in digital cable or satellite signals). If you already have an HDTV set that you think is not so hot in this regard, you might be a candidate for an outboard scaler or a receiver or preamp that features high-performance video scaling (look for names such as Silicon Optix, Gennum, or Faroudja).

Rules to Process By Here are some basic guidelines to help you navigate the wilderness of video upconversion:

• Always start with the best connection you can. HDMI (or DVI) usually is best, followed by component-video, S-video, composite-video, and RF, in that order. • Remember that video transcoding in an A/V receiver or preamplifier is a convenience, not a magic picture-improver. Converting a composite-video signal to component-video or HDMI will not make it better. • You can't get a good picture on today's fixed-pixel (plasma, LCD, DLP, or LCoS) HDTVs without good deinterlacing. Cheap progressive-scan DVD players may do a worse job of it than your TV, so unless you know what's in your player and are confident of its quality, try it with both 480i and 480p output to see which looks better on your set. • Avoid unncessary scaling. This is a particularly important consideration if you have an upconverting DVD player or a receiver or preamp with built-in video scaling capability. If you set the output on one of these devices to anything other than your display's native resolution, the display will have to re-scale the signal. And if you have, for example, a 1,366 x 768 plasma and your upconverting DVD player or receiver, as is common, supports only ATSC-standard resolutions such as 720p and 1080i, that will not be possible. If you can't match the upconversion resolution to the display resolution, don't go beyond simple deinterlacing - let the display handle the scaling. • Never convert a 720p HDTV signal to 1080i unless you absolutely have to. Interlacing a 720p signal loses, irretrievably, its most special quality. If you are using an HD cable or satellite TV box, set its video output to "native" mode if it has one. That will send video out in the same format it was broadcast. If the box requires you to select an output resolution, choose 720p unless you have a CRT-based HDTV; then you should choose 1080i. If you have a 1080p display, you might want to try both 720p and 1080i and see which looks better to you on most of the programs you watch, or you could switch the box's output resolution based on the channel you're watching (720p for 720p networks such as ABC, ESPN, and Fox, 1080i for 1080i networks such as NBC and CBS).

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