A test card, also known as a test pattern in North America, 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). Originally, all test cards were actually 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 nowadays generated by test signal generators, which do not depend on the correct configuration of (and presence of) a camera. Digitally-generated cards allow vendors, viewers and television stations to adjust their equipment for optimal functionality; while older camera-generated and kinescope-generated cards provided a reasonably good reference. They have been shown since the earliest TV broadcasts by all American and Canadian television networks, the BBC, Baird Television and Marconi E.M.I systems.

The test card usually has a set of line-up patterns, enabling television cameras to be adjusted to show the picture correctly. (Compare with SMPTE color bars.) Most 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. SMPTE bars—and several other test cards—include analog black (a flat waveform at 7.5 IRE, or the NTSC setup level), full white (100IRE), and a "sub-black" or "blacker-than-black" (at 0 IRE), which represents the lowest low-frequency transmission voltage permissible in NTSC broadcast (though the negative excursions of the colorburst signal may go below 0 IRE). Between the color bars and proper adjustment of brightness and contrast controls to the limits of perception of the first sub-black bar, an analog receiver (or other equipment like VTRs) may be adjusted to provide impressive fidelity.

They would also typically be broadcast to a background of specially composed music (to avoid having to pay licensing fees for existing compositions), a tone, or the relayed broadcasting of a radio station also owned by the same broadcaster. There is now a cult following for test-card music.

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