Editing Test card (section)

==History==
[[File:Indian Head Test Pattern with Labels.png|thumb|upright=1.3|The famous RCA [[Indian-head test pattern]] used mainly in North America from 1940 to the 1970s with its elements labelled, describing the use of each element in aligning a black & white analog TV&nbsp;receiver.]]
[[File:RTF Test card 819-lines 1953.jpg|thumb|First [[Radiodiffusion-Télévision Française|RTF]] test card (1953) for the French [[819 line|819-line]] TV system. Also used in [[French Algeria]], with modifications also used by [[TMC (TV channel)|TMC]] in [[Monaco]],<ref>{{cite web | url=https://forum.retrotechnique.org/t/mires-tv-francaises-anciennes/81275?page=2 | title=Mires TV françaises anciennes | date=5 December 2019 }}</ref> [[Telesaar]] in the [[Saar Protectorate]],<ref>{{cite web | url=https://saar-nostalgie.de/Telesaar.htm | title=Telesaar }}</ref> and [[Televisión Nacional de Chile|TVN]] in [[Chile]]<ref>{{Cite web | url=https://www.worldradiohistory.com/hd2/IDX-UK/Technology/Technology-All-Eras/Archive-Practical-Television-IDX/70s/Television-Servicing-UK-1974-02-OCR-Page-0033.pdf | title=Pirate TV | website=www.worldradiohistory.com}}</ref>]]
[[File:SW Testbild auf Philips TD1410U.jpg|thumb|upright|A 1952 Philips TD1410U television set showing the optical monochrome [[Telefunken T05]] test card.]]

Test cards are as old as TV broadcasts, with documented use by the BBC in the United Kingdom in its early [[Mechanical television|30-line mechanical]] [[John Logie Baird|Baird]] transmissions from 1934 and later on as simplified "tuning signals" shown before [[Sign-on and sign-off|startup]]<ref>{{cite web|title=BBC Tuning Signals |url=http://www.meldrum.co.uk/mhp/testcard/bbc_tune.html |date=29 March 2000 |publisher=Meldrum |access-date=13 February 2022 |archive-url=https://web.archive.org/web/20090223154155/http://www.meldrum.co.uk/mhp/testcard/bbc_tune.html |archive-date=23 February 2009 }}</ref> as well as in [[German military administration in occupied France during World War II|Occupied France]] during World War II.<ref name="auto">{{cite web|url=https://www.vivelapub.fr/retrospective-la-mire-tv/|title=Rétrospective: la mire à la télévision (1953 – 2002)|date=January 5, 2012|website=VivelaPub}}</ref> They evolved to include gratings for resolution testing, grids to assist with picture geometry adjustments, and grayscale for brightness and contrast adjustments. For example, all these elements can be seen in a [[Radiodiffusion-Télévision Française]] [[819 line|819-line]] test card introduced in 1953.<ref name="auto"/>

In North America, most test cards such as the famous [[Indian-head test pattern]] of the 1950s and 1960s have long since been relegated to history. The [[SMPTE color bars]] occasionally turn up, but with most North American broadcasters now following a 24-hour schedule, these too have become a rare sight.

With the introduction of color TV, electronically generated test cards were introduced. They are named after their generating equipment (ex: [[Grundig]] VG1000,<ref>{{Cite web|url=https://patents.google.com/patent/EP0122124A3/zh|title=Test signal generator}}</ref><ref>{{cite web|url=https://all-guidesbox.com/manual/370365/grundig-72010-016-80-network-card-52.html?page=30|title=Grundig 72010-016.80 TV Service manual PDF View/Download, Page # 30|website=all-guidesbox.com}}</ref> [[Philips PM5544]],<ref>{{cite web|url=https://frank.pocnet.net/other/sos/Philips_PM5544_PM3400_Publication.pdf#page=3 |title=Combined colour/monochrome pattern generator PM 5544}}</ref> [[Telefunken FuBK]],<ref>{{cite web|url=https://books.google.com/books?id=J61AAQAAIAAJ&q=%22FuBK%22+-wikipedia|title=EBU Review|first=European Broadcasting|last=Union|date=February 6, 1988|publisher=Administrative Office of the European Broadcasting Union|via=Google Books}}</ref> etc.), TV station (ex: [[List of BBC test cards|BBC test card]]) or organization (ex: [[SMPTE color bars]], [[EBU colour bars]]).

In [[developed country|developed countries]] such as [[Australia]], [[Canada]], the [[United Kingdom]], and the [[United States]], the financial imperatives of commercial television broadcasting mean that air-time is now typically filled with programmes and commercials (such as [[infomercial]]s) 24 hours a day, and non-commercial broadcasters have to match this.

A late test card design, introduced in 2005 and fully adapted for HD, SD, 16:9 and 4:3 broadcasts, is defined on ITU-R Rec. BT.1729.<ref>{{cite web|url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1729-0-200504-I!!PDF-E.pdf |title=ITU-R Rec. BT.1729}}</ref> It offers markings specificity design to test format conversions, chroma sampling, etc.

Formerly a common sight, test cards are now only rarely seen outside of television studios, post-production, and distribution facilities. In particular, they are no longer intended to assist viewers in calibration of television sets. Several factors have led to their demise for this purpose:
* Modern [[microcontroller]]-controlled analogue televisions rarely if ever need adjustment, so test cards are much less important than previously. Likewise, modern cameras and camcorders seldom need adjustment for technical accuracy, though they are often adjusted to compensate for scene light levels, and for various artistic effects.
* Use of digital interconnect standards, such as [[CCIR 601]] and [[SMPTE 292M]], which operate without the non-linearities and other issues inherent to analog broadcasting, do not introduce color shifts or brightness changes; thus the requirement to detect and compensate for them using this reference signal has been virtually eliminated. (Compare with the obsolescence of [[stroboscope]]s as used to adjust the speed of record players.) On the other hand, digital test signal generators do include test signals which are intended to stress the digital interface, and many sophisticated generators allow the insertion of [[jitter]], bit errors, and other pathological conditions that can cause a digital interface to fail.
* Likewise, use of digital broadcasting standards, such as [[Digital Video Broadcasting|DVB]] and [[ATSC standards|ATSC]], eliminates the issues introduced by modulation and demodulation of analog signals.
* Test cards including large circles were used to confirm the linearity of the set's deflection systems. As solid-state components replaced [[vacuum tube]]s in receiver deflection circuits, linearity adjustments were less frequently required (few newer sets have user-adjustable "VERT SIZE" and "VERT LIN" controls, for example). In LCD and other deflectionless displays, the linearity is a function of the display panel's manufacturing quality; for the display to work, the tolerances will already be far tighter than human perception.

For custom-designed video installations, such as [[LED displays]] in buildings or at live events, some test images are custom-made to fit the specific size and shape of the setup in question. These custom test images can also be an opportunity for the technicians to hide inside jokes for the crew to see while installing equipment for a show.<ref name="claiborne" />
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