Most modern test cards include a set of calibrated color bars which will produce a characteristic pattern of "dot landings" on a vectorscope, allowing chroma and tint to be precisely adjusted between generations of videotape or network feeds. Test cards typically contain a set of patterns to enable television cameras and receivers to be adjusted to show the picture correctly (see SMPTE color bars). More recently, the use of test cards has also expanded beyond television to other digital displays such as large LED walls and video projectors. The audio broadcast while test cards are shown is typically a sine wave tone, radio (if associated or affiliated with the television channel) or music (usually instrumental, though some also broadcast with jazz or popular music).ĭigitally generated cards came later, associated with digital television, and add a few features specific of digital signals, like checking for error correction, chroma subsampling, aspect ratio signaling, surround sound, etc. These patterns are specially tailored to be used in conjunction with devices such as a vectorscope, allowing precise adjustments of image equipment. These are generated by test signal generators, which do not depend on the correct configuration (and presence) of a camera, and can also test for additional parameters such as correct color decoding, sync, frames per second, and frequency response.
From the 1950s, test card images were built into monoscope tubes which freed up the use of TV cameras which would otherwise have to be rotated to continuously broadcast physical test cards during downtime hours.Įlectronically generated test patterns, used for calibrating or troubleshooting the downstream signal path, were introduced in the late-1960s.
Such cards are still often used for calibration, alignment, and matching of cameras and camcorders.
Used since the earliest TV broadcasts, test cards were originally physical cards at which a television camera was pointed, allowing for simple adjustments of picture quality. A test card, also known as a test pattern or start-up/closedown test, is a television test signal, typically broadcast at times when the transmitter is active but no program is being broadcast (often at sign-on and sign-off).
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