Television test patterns

To the Internet generation, it looks like a bizarre screen saver. But to late-night and early-morning TV viewers of an earlier age, this was an all-too-familiar sign that a TV station was off the air.

This famous "Indian Head" black-and-white test pattern was introduced by RCA in 1939. Its purpose: to help people adjust their television sets. The detailed patterns let people fine-tune the focus, frequency, resolution, and overall picture on their TVs.

"TV sets don't require the kind of calibration that they used to," says Mike Keller, director of engineering at Boston's WCVB-TV. "Most people now just adjust [things like color] to their eye."

As required by the Federal Communications Commission, however, test patterns continue. The new pattern (a series of color bars) is broadcast continuously. If you could "roll" your TV picture, you'd see the thin Vertical Interval Test Signal, or VITS. It is how stations monitor such things as color, hue, and saturation.

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