Early in August, The New York Times ran an article proclaiming the end of the picture tube. Cathode-ray tubes (CRTs) are "heading for the dustbin of history much faster than anyone expected," wrote our colleague and contributor Eric Taub. But unlike a dead-end technology like the SACD — whose death I proclaimed in my last column — many characteristics of the CRT live on in HDTV systems.

Way back in 1940, Vladimir Zworykin, a pioneer in the development and commercialization of television, said in his early textbook on TV that the CRT "will continue to keep step with the inevitable advance of television standards." He would probably be as impressed with the technology's 66-year-plus longevity as I am. Zworykin would also be the first to recognize those capabilities and limitations of picture-tube technology that have survived into the HDTV era.

Take scanning, for instance — the process by which an image is disassembled in a camera and reassembled on a TV tube. The concept of line-by-line scanning was fundamental to early television because it was used in both the image sensors (such as Zworykin's Iconoscope, a sort of picture tube in reverse) and in display CRTs. We still speak of pictures being built up of scan lines, even though solid-state CCD image sensors in video cameras, as well as all fixed-pixel display technologies (LCD, DLP, LCoS, plasma), don't have to scan the image line by line — they all sense or display an entire frame all at once. In principle, you could directly hook up a 1080-line CCD camera to a 1080-line fixed-pixel display on a pixel-by-pixel basis, though it would take a couple of million cables! Other CRT-derived systems similarly survive into HDTV, including interlaced video encoding and the precise shades of the red, green, and blue primary colors for HDTV (derived from CRT-phosphor colors).

While CRTs won't be missed by anyone with a small apartment, there are people already very concerned about the eventual shutdown of CRT production lines — those whose profession requires them to monitor video quality for transmission or mastering purposes. Almost all of these folks are now making decisions about video quality using relatively small CRT monitors. This isn't a bad thing, since no fixed-pixel technology can reproduce the whole video dynamic range quite as smoothly as a CRT with its truly black blacks.

But even the largest of the studio-grade CRT-based direct-view HDTV monitors, Sony's BVMA32, measures only 32 inches diagonally, far smaller than a great many of the HDTV fixed-pixel displays already in homes. And while the image it can generate when reproducing HD video can be gloriously realistic — like looking through an open window — its relatively small size can hide defects in the image that may become obvious when enlarged in a home theater. Furthermore, since the BVMA32 costs $42,850, not all studios working on DVDs or HD video can afford one, with the result that many video-quality decisions are made using far less capable devices, all CRT monitors.

The research and development of all the major video-codec systems (MPEG-2, MPEG-4/H.264, and VC-1) used in DVD or high-definition media were conducted with images monitored on CRTs. Crucial decisions as to how these systems work, especially in how they're structured to minimize the visibility of encoding artifacts, were made using CRTs. So while it's hard to find an explicit expression of CRT technology in these video codec systems, their very architectures and operation were influenced by CRT characteristics, for good or ill.

This only starts to become a problem when you watch media at home. To the extent that your monitor or TV deviates from CRT-like size and visual behavior, you may see increasing problems with an image that looked fine when it left the mastering studio. I've found encoding artifacts such as mosquito noise and blocking to be more visible with fixed-pixel technologies than they are with CRTs of the same size, at least with material of DVD resolution.

What the pro-video folks desperately need is a fixed-pixel technology that produces very large, CRT-like images. Zworykin seems to have been prescient when he wrote 66 years ago: "Today, owing largely to the advent of cathode-ray television systems, a recognizable picture can be taken for granted, and the problem is one of obtaining a high-definition picture."

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