Test card

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SMPTE Color Bars.svg
SMPTE colour bars: common NTSC test pattern
Philips PM5544.svg
PM5544: common PAL test pattern
EBU Colorbars.svg
EBU test card (4:3)

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). 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, and can also test for additional parameters such as sync, frames per second, and frequency. [1] 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 jazz or popular music). More recently, the use of test cards has also expanded beyond television to other digital displays such as large LED walls and video projectors.

Contents

Technical details

Test cards typically contain a set of patterns to enable television cameras and receivers to be adjusted to show the picture correctly (see SMPTE colour bars). Most modern test cards include a set of calibrated colour 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 (100 IRE), and a "sub-black", or "blacker-than-black" (at 0 IRE), which represents the lowest low-frequency transmission voltage permissible in NTSC broadcasts (though the negative excursions of the colourburst signal may go below 0 IRE). Between the colour bars and proper adjustment of brightness and contrast controls to the limits of perception of the first sub-black bar, an analogue receiver (or other equipment such as VTRs) can be adjusted to provide impressive fidelity.

They are also used in the broader context of video displays for concerts and live events. There are a variety of different test patterns, each testing a specific technical parameter: gradient monotone bars for testing brightness and colour; a crosshatch pattern for aspect ratio, alignment, focus, and convergence; and a single-pixel border for over-scanning and dimensions. [1]

History

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 analogue TV receiver. Indian head test pattern labeled.png
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 analogue TV receiver.
A 1952 Philips TD1410U television set showing the optical monochrome Telefunken test card T05. SW Testbild auf Philips TD1410U.jpg
A 1952 Philips TD1410U television set showing the optical monochrome Telefunken test card T05.

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:

In 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 infomercials) 24 hours a day, and non-commercial broadcasters have to match this.

In North America, most test cards such as the famous Indian-head test pattern of the 1950s and 1960s have long been relegated to history. The SMPTE colour bars occasionally turn up, but with most North American broadcasters now following a 24-hour schedule, these too have become a rare sight. 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. [1]

Monoscope

Rather than physical test cards, which had to be televised using a camera, television stations often used a special purpose camera tube which had the test pattern painted on the inside screen of the tube. Each tube was only capable of generating the one test image, hence it was called a monoscope.

Monoscopes were similar in construction to an ordinary cathode ray tube (CRT), only instead of displaying an image on its screen it scanned a built-in image. The monoscope contained a formed metal target in place of the phosphor coating at its "screen" end and as the electron beam scanned the target, rather than displaying an image, a varying electrical signal was produced generating a video signal from the etched pattern. Monoscope tubes had the advantage over test cards that a full TV camera was not needed, and the image was always properly framed and in focus. They fell out of use in the 1960s as they were not able to produce colour images.

Test patterns for photocopiers

A lesser-known kind of test pattern is used for the calibration of photocopiers. [2] [3] Photocopier test patterns are physical sheets that are photocopied, with the difference in the resulting photocopy revealing any telltale deviations or defects in the machine's ability to copy.

In numismatics

Television has had such an impact in today's life that it has been the main motif for numerous collectors' coins and medals. One of the most recent examples is The 50 Years of Television commemorative coin minted on 9 March 2005, in Austria. The obverse of the coin shows a "test pattern", while the reverse shows several milestones in the history of television.

The Philips Pattern is widely recognized as one of the iconic popular culture symbols of the 1980s and 1990s. Numerous novelty and collectible items has been patterned after the famous test card, including wall clocks, bedsheets, wristwatches, and clothing.

The BBC Test Card F features throughout 2006-07 TV sci-fi detective series Life on Mars . [4] [5]

Test card music

In Britain, music - rather than radio sound - was usually played with the test card. The music played by the BBC, and afterwards ITV, was library music, which was licensed on more favourable terms for frequent use than commercially available alternatives. Later, Channel 4 used UK library LPs from publishers like KPM, Joseph Weinberger and Ready Music. [6]

Until September 1955, the BBC used live playing 78 RPM commercial records as an audio background to the test cards. After that date, they switched to using recorded music on tape. [7] The following year, the BBC began to build up its own library of specially produced music for the half hour tapes - initially three tunes in similar style, followed by an identification sign (the three notes B-B-C played on celesta). ITV (which began its first trade transmissions in 1957) continued to use commercially available recordings until the late 1960s, when it also began to make specially produced tapes. [7]

For rights reasons, much of the music was recorded by light music orchestras in France and Germany, though sometimes by British musicians, or top international session players using pseudonyms, such as The Oscar Brandenburg Orchestra (an amalgamation of Neil Richardson, Alan Moorhouse and Johnny Pearson) or the Stuttgart Studio Orchestra. [8] Other composers and bandleaders commissioned for this type of work included Gordon Langford, Ernest Tomlinson. Roger Roger, Heinz Kiessling, Werner Tautz, Frank Chacksfield and Syd Dale.

During the 1980s, the test card was gradually seen less and less - it was pushed out first by Teletext pages, then extended programme hours. The same tapes were used to accompany both the test card and Ceefax on BBC channels, but some fans argue that new tapes introduced after Ceefax became the norm in 1983 were less musically interesting. [7]

See also

Related Research Articles

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PAL Colour encoding system for analogue television

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Test Card F Test card used by BBC television for decades

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Indian-head test pattern Television test card

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Monoscope

A monoscope was a special form of video camera tube which displayed a single still video image. The image was built into the tube, hence the name. The tube resembled a small cathode ray tube (CRT). Monoscopes were used beginning in the 1950s to generate TV test patterns and station logos. This type of test card generation system was technologically obsolete by the 1980s.

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Philips PM5544 TV test pattern, used to be widely used in European (PAL) countries

The Philips PM5544 is a television pattern generator, most commonly used to provide a television station with a complex test card commonly referred to as a Philips Pattern or PTV Circle pattern. The content and layout of the pattern was designed by engineer Finn Hendil in the Philips TV laboratory in Copenhagen under supervision of chief engineer Erik Helmer Nielsen in 1966–67. The equipment, the PM5544 Test Pattern Generator, which generates the pattern, was made by engineer Finn Hendil and his group in 1968–69. Since the introduction of the PM5544 in the early 1970s, the Philips Pattern has become one of the most commonly used test cards, with only the SMPTE bars, the BBC Test Card F and the Snell & Wilcox Zone Plate coming close to its usage.

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Black and burst Analogue synchronization signal used in broadcasting

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References

  1. 1 2 3 Claiborne, Vickie (9 November 2019). "Video Testing Images". PLSN. Retrieved 16 March 2020.
  2. "Samsung SF531P PCSTATS Review – Printer Test Patterns". Pcstats.com. 2007-10-15. Retrieved 2010-01-01.
  3. "Projection: Room A / Room B". Thing.net. Retrieved 2010-01-01.
  4. "Life on Mars questions". BBC Drama. Retrieved 24 July 2020.
  5. Griffiths, Nick (1 April 2007). "Did you spot the clues?". The Radio Times. Archived from the original on 21 November 2008.
  6. Currie, Tony. 'The Girl, The Doll, The Music' (1998), essay included as the notes for Test Card Classics, Chandos CD FBCD 2000
  7. 1 2 3 Roberts, Neville. A History of Test Card Music
  8. 'Royal Daffodil' by Gordon Langford. performed by the Stuttgart Studio Orchestra, conducted by Ralph Elman