What is "test card"

n. 1 (context optometry English) A card printed with various letters or symbols, used in testing vision. 2 (context UK television English) A test signal, typically broadcast at times when the transmitter is active but no programme is being broadcast (often at startup and closedown).

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 startup and closedown). Used since the earliest TV broadcasts, test cards were originally physical cards at which a television camera was pointed, and such cards are still often used for calibration, alignment, and matching of cameras and camcorders. Test patterns used for calibrating or troubleshooting the downstream signal path are these days generated by test signal generators, which do not depend on the correct configuration (and presence) of a camera. Digitally generated cards allow vendors, viewers and television stations to adjust their equipment for optimal functionality. 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 popular music).