By Peter J. Restivo
TORONTO

This is something every HDTV production company needs to know.  For some 100 years, motion picture photographers have been using grayscale test charts to assist in making consistent high-quality pictures and matching images in multicamera studios and locations.

In the 1940s, similar test charts became standard in television.  The aim has always been standardization - getting all the cameras to "see" and reproduce images equally.

That is easier said than done.

David Corley, founder and president of Toronto's DSC Labs, said that in real-world television production, standardization is more a case of what you can get cameras to agree on.

"If you have four cameras on set and they only match if shaded to slightly blue, then slightly blue is what the home viewer gets."

While the subject may seem a bit esoteric, it is vital to HDTV production, where every difference and flaw is highlighted and magnified.  To keep standards high in the high-def realm, Corley has developed a system that does not "see" the test image so much as generate it.  The system, now the standard at ABC and NBC, has been trademarked as the Optical Signal Generator.

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It was CBC's (Canadian Broadcasting Corp.) pioneering work that motivated DSC to develop the first reliable color test materials in the 1960s.  Corley recalls CBC's Roger Ross having problems because CBC was using black-and-white slides in its telecines.

Corley discovered that the silver grains on the black-and-white slides scatter more blue light than they do red and green.  If you lined up with a B&W slide, the result would not be the neutral alignment needed for proper color rendition and accurate blacks and whites.

To solve the problem, DSC developed a grayscale slide in color that became the network standard.

Today's CCD cameras, some with contrast ranges of 3,000:1, require a new approach to picture testing in studios with diverse lighting arrangements - from simple newscasts with single robotic camera to multicamera "Saturday Night Live" configurations.

Paul Kopcienski, supervisor for Studio Maintenance at NBC's "Saturday Night Live," said: "Prior to the DSC charts, there was no way of getting true vectorscope readings from cameras in real locations."

"Modern cameras can self-generate testing tools such as color bars, but the truest test is to set up the camera on a chart under the exact lighting conditions to be used in the production," he said.

"Lots of old timers often try to set up cameras by eye, and it works much of the time," Kopcienski said.  "But for top-quality performance, you need charts to paint the cameras.  Previous methods permitted you to chart for black, white and grayscale, but this permits actual vectorscope alignment, exact matches of cameras."

Chuck Pharis, senior video engineer for ABC in Los Angeles, takes the issue of charting in multicamera production a step beyond.  With more than 30 years  in television engineering, Pharis works the 48-camera Super Bowl and more recently "Monday Night Football," which was the first live, regularly scheduled HDTV (720p) sporting event in prime time.

"HDTV is great," Pharis said, "but you have to understand the demands on picture quality are greater than ever before.  People are routinely watching on screens 30 inches or bigger now.  And HDTV's 16:9 format uses more of the lens than ever before.  Remember the lens is round, 16:9 is not."

Networks chart studio and location cameras for every show.  Multiple cameras must match, and it's more than a matter of getting the flesh tones correct.  In the good old days, producers and directors gave the tech types just enough time to chart cameras on the old nine step grayscale devices.  Today, some operations have moved up to the 11-step grayscale charts.  However, with broadcast camera capability well beyond 1,000:1 in contrast ratio, even the 11-step charts do not permit shading to maximize system potential because they often cause setups to compress the grayscale.

For DSC's David Corley, these are not simply charts, they are signal generators.  He trademarked them as Optical Signal Generators.  Indeed, that's exactly what they are.  They don't "see" the test image; they generate it.  DSC's front-lit and rear-lit units render even illumination across the entire range of white to black without flare.  Flare, Corley said, leads to dangerously misleading results.  "Even matte charts don't yield the professional results of our charts."

Chart manufacturers traditionally produce their products using a print-on-matte process similar to that found in newspapers and magazines.  It's a dot pattern arrangement.  That worked reasonably well on Plumbicon tube cameras, but such printed charts create a whole new ballpark of problems with CCD pickup devices.  They create moire and other distortions that ultimately diminish picture quality.  DSC's front-lit 16:9 charts use CCD-friendly random-dot patterns and are multipattern charts with grayscale and color chips that generate signals that will line up precisely in the primary and secondary vectorscope boxes.  ABC's Chuck Pharis says sometimes a good engineer can "eyeball" the primary colors (red, blue, green), "but you can't get the secondary colors (cyan, magenta, yellow) crucial to superior color images."

One detail built into DSC charts - a deep black box that renders absolute black even on a sunny day in a football stadium.

DSC charts are easy to use in the studio but rugged enough for tough location shoots.  Pharis often hauls them around football stadiums in golf carts.  The DSC Ambi line of portable, stand-mounted rear-lit OSG units utilize the set light from below, above or behind rendering an evenly lit chart anywhere.  They work especially well on sets and locations where there is a mixture of light ranging from florescent to HMI.  The Ambi units utilize color and gray chips individually manufactured to exacting standards from continuous tone transparencies; they are not printed.  No dots.

Corley points to another important use of his unique charts: film production for television.  By shooting even a few frames of his Combi test chart on film in each scene, a colorist in post production can evenly match every scene of a made-for-TV movie.

Corley suggests that even with things digital and HDTV, "What's old is new again, especially if new technology helps make it new again."