A NEW APPROACH to video/RGB switching
Apr 1, 1999 12:00 PM, Pete Putman
Whenever professional A-V dealers get together these days, the subject inevitably gets around to competition from resellers of PCs and their ability to move into the A-V systems integration business. Some proclaim doom; others scoff at the possibility. Admittedly, items like automated mixers and video/data projectors are becoming more plug-and-play with each passing year, and it is conceivable that some precocious PC systems integrators may be able to figure out how to sell a simple installation and pull it off, particularly with the slow migration of video and audio devices to serial digital inputs and outputs. The fact remains, however, that we still live in an analog world when it comes to signal distribution. How we choose to port signals around a facility may change, but the laws of physics remain constant. In fact, our cabling options-particularly those for video-are more complex than ever, thanks to wider use of component video from computers and video sources. The wild card is digital signal distribution. It does not matter if a digital signal is composite or component video; it needs only one cable to move from point A to point B. The D/A converters act as virtual switchers, decoding and processing the RGBS, RGBHV or YUV signal elements. When every large-screen display has direct serial digital inputs, the single-cable signal distribution environment will become reality, but that is some time off in the future.
Some of the major decisions we face today arise from connection and switching options provided by the fast-growing family of desktop and boardroom LCD and DLP projection systems. These boxes can do it all, jumping from composite video to workstation graphics to notebook computer signals with surprising agility, stereo audio following in lockstep. Does it make sense to use a projector as the switching hub? What about the different component formats? How about audio-follow switching? Should it be done separately? Are there ways to achieve smoother switching without glitches when moving between video and computer sources? These are all legitimate questions.
Today, we can move video as a composite baseband signal, a two-channel (Y/C) S-Video signal, and as a three-channel (YUV) signal. If the video source is a composite format-like VHS or laserdisc-S-Video signal distribution has little benefit. The decoded color/luminance artifacts will be present, no matter how you handle the signal. In these cases, single-cable distribution makes the most sense.
For sources that provide S-Video and YUV component outputs-DVD, Betacam, M II and component laserdisc-the difference between running two cables and three is a matter of economics and consumer demand. The advantage of a multi-wire system is that both YUV and RGB video can be ported down the same path. If you are looking for future compatibility, HDTV signals will be moved in only two ways-as single-cable digital bitstreams or as decoded analog (Y Pb Pr), requiring three cables.
Where do you switch all of these signals? With a stand-alone box or in a projector or other large-screen display? One obvious problem with using a projector or monitor for switching is that if it must be serviced, you lose your switch and patch point. Outboard switchers capable of handling every possible composite and component signal are reliable and inexpensive enough that it makes more sense to use them. Many have audio-follow connections, too.
As we sit and contemplate how to design a system that can accommodate single- and multi-wire video signals, along comes a new product that can simplify the job in a way not seen before. Manufacturers are combining conventional RGB switchers with digital video scalars, resulting in a scalar/switcher, or seamless video/RGB switcher.
Here's the method behind the madness: Scaling video-composite, S-Video, or YUV/RGB-allows it to be handled like computer video signals. A scaled video signal can be converted to the same horizontal scan and frame refresh rates as a computer source, thereby providing seamless hard-cut switching between the two signals ahead of a projector or display, with no loss of picture sync and no "blank" screens waiting for the projector to scan and lock on to the input signal.
Like any other switcher, these products will be RS-232 compatible for remote operation, and only a single RGBHV cable needs to be run to the projector or monitor. Best of all, the transitions between video and computer signals will be instantaneous and smooth with a scalar/ switcher-something that rarely happens when selecting video and computer inputs from the projector. Once the projector locks up to the scalars' sync output, the transitions are as smooth as a genlocked video cut.
A good analogy would be converting a mix of audio lines-unbalanced Hi-Z, balanced, mic and line levels-all to three-wire balanced audio with consistent levels. That is a much easier trick to manage with audio, though. Video and computer signals have such a dizzying variety of sync and refresh rates that the thought of trying to achieve smooth cuts (yes, and even dissolves) between them sends lesser engineers into fits.
Scalar/switchers also allow the best resolution and sync match to the display. For flat-matrix projectors, that will be the native resolution of the LCD or DMD imaging device. For CRT projectors and monitors, the match will be to the sweet spot or point where maximum resolution and brightness meet, such as SVGA (7 inch/178 mm), XGA (8 inch/203 mm), and SXGA (9 inch/229 mm). Not only have you done away with image instability during a transition (which your clients will love), you are always driving the display at its optimum resolution.
First-generation video scalars-like high-end units made by Faroudja and Snell & Wilcox-use one RGB input and one video input, scaling and timing the video to match the sync rates of the computer. These systems actually allow the user to mix video right onto a Windows desktop, resize it, and they even stretch it anamorphically.
For fixed-install applications, sophisticated models from RGB Spectrum (SynchroMaster series) and Folsom Research (Variable Format Converter) allow the user to customize several output resolutions and scan rates for scaled video. As a bonus, both models offer seamless dissolve/cut transitions between RGB signals and up-converted video.
With some clever programming and timing, it would not be too difficult to mix everything from videoconferencing signals, Powerpoint slides, high-resolution graphics and the latest corporate video using nothing more than a couple of upstream RGB and video switchers.
One manufacturer has actually gone ahead and incorporated a switcher into two of its scaling products. Analog Way's Smart Cut will accept composite, S-Video or component video and one RGB input. Four preset output scan rates (VGA/60, SVGA/60 + /70, XGA/60) are selectable, and the result is a seamless cut between video and computer images. Analog Way's Seamless Switcher goes even further; it can mix, fade, or dissolve between up to six different RGB computer inputs (1,600x1,280 maximum resolution), outputting them as one VGA, SVGA, or XGA signal.
If the concept of an integrated scalar/switcher catches on with other manufacturers, it will be the start of a paradigm shift in video signal distribution. The catch, of course, will be the quality of video scaling provided, although even the low-end scaling engines are outputting a better-looking image than can be had from 75% of the desktop and installation-grade flat-matrix projectors currently available.
The next step will be an all-digital scaling/switching module, accepting both analog and digital video inputs and outputting a single-cable digital bitstream, compatible with one of the new digital RGB video standards being proposed by Intel and other companies. After that?
Economies of scale in manufacturing and lowered costs will make it feasible to incorporate high-quality scaling/switching into future flat-matrix projectors and monitors. Digital outputs and inputs will mean a single-cable wiring infrastructure, which might be coax, CAT-3, or CAT-5 wire - even fiber optics.
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