Editing Test card (section)

{{Short description|Test signal in television broadcasting}}
{{redirect|Test pattern||Test Pattern (disambiguation)}}
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| caption1 = [[SMPTE color bars]]: common [[NTSC]] test pattern
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| caption2 = [[Philips PM5544|PM5544]]: common [[PAL]] test pattern
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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]]).<ref>{{cite web|url=http://www.testcardcircle.org.uk/tchistory.html|title=TCC - A Very Concise History of Test Cards|website=www.testcardcircle.org.uk}}</ref>

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.<ref>{{Cite web|url=https://dictionary.cambridge.org/dictionary/english/test-card|title=TEST CARD &#124; English meaning - Cambridge Dictionary}}</ref> Such cards are still often used for calibration, alignment, and matching of cameras and [[camcorder]]s. 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.

Electronically generated test patterns, used for calibrating or troubleshooting the downstream signal path, were introduced in the late-1960s, and became commonly used from the 1970s and 80s. These are generated by test [[signal generator]]s, 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,  [[Audio-to-video synchronization|sync]], [[frames per second]], and frequency response.<ref name="claiborne" /> These patterns are specially tailored to be used in conjunction with devices such as a [[vectorscope]], allowing precise adjustments of image equipment.

The audio broadcast while test cards are shown is typically a [[sine wave]] tone, [[Radio broadcasting|radio]] (if associated or affiliated with the television channel) or [[Production music|music]] (usually [[instrumental music|instrumental]], though some also broadcast with [[jazz]] or [[popular music]]).

Digitally generated cards came later, associated with [[digital television]], and add a few features specific of digital signals, like checking for [[error correction]], [[chroma subsampling]], [[Active Format Description|aspect ratio signaling]], [[5.1 surround sound|surround sound]], etc. More recently, the use of test cards has also expanded beyond television to other digital displays such as large [[LED display|LED walls]] and [[video projector]]s.<ref name="claiborne" />