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).[1]
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.[2] Such cards are still often used for calibration, alignment, and matching of cameras and camcorders. 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 generators, 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, sync, frames per second, and frequency response.[3] 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 (if associated or affiliated with the television channel) or music (usually instrumental, though some also broadcast with jazz or popular music).
Test cards typically contain a set of patterns to enable television cameras and receivers to be adjusted to show the picture correctly (see SMPTE color bars). Most modern test cards 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 (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 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 such as VTRs) can be adjusted to provide impressive fidelity.
Test cards have also been used to determine actual coverage contours for new television broadcasting antennas and/or networks. In preparation for the new commercial ITV service in the 1950s, the Independent Television Authority (ITA) tasked Belling & Lee, an Enfield-based British electronics company best known for inventing the Belling-Lee connector just over three decades earlier, with designing a series of Pilot Test Transmission test cards and slides[4] intended for potential viewers and DX-enthusiasts to test the ITA's new Band IIIVHF transmitter network that was designed with the assistance of the General Post Office (GPO), then the UK's government-run PTT agency. These test cards, some featuring the G9AED call sign assigned by the GPO for said transmissions, featured a squiggly line in a circle in the middle of the test card with an on-screen line gauge indicated in miles which was used as a guide to reveal the distance between the receiver, the (temporary) transmitter and a replicating landscape feature causing ghosting. Said test cards were mainly transmitted from temporary mobile transmitters attached to caravan trailers based at the predicted locations of the ITA's eventual main transmitters, such as Croydon, Lichfield, Emley Moor and Winter Hill.[5][6] Almost a decade later, the BBC started using a modified SMPTE monochrome test card radiating from the Crystal Palace transmitter to test its new UHF network which it eventually launched as BBC Two in 1964.
Test cards 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 color; a crosshatch pattern for aspect ratio, alignment, focus, and convergence; and a single-pixel border for over-scanning and dimensions.[3]
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 analog TVreceiver.First RTF test card (1953) for the French 819-line TV system. Also used in French Algeria, with modifications also used by TMC in Monaco, Telesaar in the Saar Protectorate, and TVN in ChileA 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 30-line mechanicalBaird transmissions from 1934 and later on as simplified "tuning signals" shown before startup[10] as well as in Occupied France during World War II.[11] 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 Française819-line test card introduced in 1953.[11]
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.
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.
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.[16] 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 stroboscopes 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 DVB and 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 tubes 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.[3]
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 after the 1960s as they were not able to produce color images.
A lesser-known kind of test pattern is used for the calibration of photocopiers.[17][18] Photocopier test patterns are physical sheets that are photocopied, with the difference in the resulting photocopy revealing any tell-tale deviations or defects in the machine's ability to copy.
There are also test patterns kits and software developed specifically for many consumer electronics. The B&K Television Analyst was developed in the 1960s for testing monochrome TV sets in the NTSC standard and was later modified for European and Australian PAL standards. Among other uses, it consisted of a flying spot scanner on which a test pattern printed on a cellulose acetate slide was shown.[19]
When CRT monitors were still commonly used on personal computers, specific test patterns were created for proper calibration of such monitors in the cases whereby multimedia images could not be shown properly on said monitors.[20] Some VCD and DVD lens cleaner discs, such as the Kyowa Sonic lens cleaning kits from 1997–2001, also included test patterns as well.[21]
More recent examples include the THX Optimizer which can be accessed in the setup menu in almost every THX-certified DVD,[22][23] as well as well as the "HDR sRGB Graphics Test (400 nits)" and "Test Patterns" series available on Netflix[24] meant to test out streaming bandwidth on Internet-enabled devices,[25] especially on widescreen smartHDR TVs, 4K and 8K displays and also used to sync audio and video feeds, which can be affected, among other factors, by Bluetooth and Internet latency.[26]
Test patterns are also used to calibrate CCTV cameras and monitors,[27] as well as medical imaging displays and equipment for telemedicine and diagnostic purposes,[28] such as the SMPTE RP-133 medical diagnostic imaging test pattern specification for medical and surgical displays, created around 1983[29]–86;[30][31] as well as a later derivative called the TG18-QC test pattern created by the AAPM in 2001.[32][33] Test patterns to calibrate X-raymachines, in particular those manufactured by Leeds Test Objects in England, also exist as well.[34][35]
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 the centre portion of the Telefunken T05 test card, while the reverse shows several milestones in the history of television.[36]
In popular culture
The Philips Pattern is widely recognised 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.
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.[39] Later, Channel 4 used UK library LPs from publishers like KPM, Joseph Weinberger and Ready Music.[40]
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.[41] 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.[41]
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.[42] 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.[43]
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.[41]
List of TV test cards
A newly built television set undergoing image calibration using a test card at a Grundig factory in Nuremberg, West Germany (December 1959)A 1940s-style "bullseye" test pattern exhibited at the Early Television Museum in Hilliard, Ohio (June 2022)
Chequerboard optical[70] and electronic "tea towel"[71] test cards (1950s/60s, monochrome, 625-lines, used in varying forms in West Germany, Italy, Netherlands, Soviet Union, Portugal and Spain)
SMPTE optical monochrome test card (1950s?, 525-lines; 1962–1964,[72] 625-lines)[73]
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
NTSC is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170.
Phase Alternating Line (PAL) is a colour encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields per second, and associated with CCIR analogue broadcast television systems B, D, G, H, I or K. The articles on analog broadcast television systems further describe frame rates, image resolution, and audio modulation.
SECAM, also written SÉCAM, is an analog color television system that was used in France, Russia and some other countries or territories of Europe and Africa. It was one of three major analog color television standards, the others being PAL and NTSC. Like PAL, a SECAM picture is also made up of 625 interlaced lines and is displayed at a rate of 25 frames per second. However, due to the way SECAM processes color information, it is not compatible with the PAL video format standard. SECAM video is composite video; the luminance and chrominance are transmitted together as one signal.
Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the characteristics of the human visual system.
Color television or colour television is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white television technology, which displays the image in shades of gray (grayscale). Television broadcasting stations and networks in most parts of the world upgraded from black-and-white to color transmission between the 1960s and the 1980s. The invention of color television standards was an important part of the history and technology of television.
SMPTE color bars are a television test pattern used where the NTSC video standard is utilized, including countries in North America. The Society of Motion Picture and Television Engineers (SMPTE) refers to the pattern as Engineering Guideline (EG) 1-1990. Its components are a known standard, and created by test pattern generators. Comparing it as received to the known standard gives video engineers an indication of how an NTSC video signal has been altered by recording or transmission and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce NTSC chrominance and luminance information correctly.
Broadcasttelevision systems are the encoding or formatting systems for the transmission and reception of terrestrial television signals.
The Indian-head test pattern is a test card that gained widespread adoption during the black-and-white television broadcasting era as an aid in the calibration of television equipment. It features a drawing of a Native American wearing a headdress surrounded by numerous graphic elements designed to test different aspects of broadcast display. The card was created by RCA to be the standard image for their TK-1 monoscope, a simple video camera capable of producing only the image embedded within it. The pattern was introduced in 1939 and over the following two decades became a fixture of television broadcast across North America in 525-line resolution and abroad in 525- and 625-line resolution until it was made obsolete by the rise of color television in the 1960s.
The Philips circle pattern refers to a family of related electronically generated complex television station colour test cards. The content and layout of the original colour circle pattern was designed by Danish engineer Finn Hendil (1939–2011) in the Philips TV & Test Equipment laboratory in Amager near Copenhagen under supervision of chief engineer Erik Helmer Nielsen in 1966–67, largely building on their previous work with the monochrome PM5540 pattern. The first piece of equipment, the PM5544 colour pattern generator, which generates the pattern, was made by Finn Hendil and his group in 1968–69. The same team would also develop the Spanish TVE colour test card in 1973.
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting. The number of television lines influences the image resolution, or quality of the picture.
A video signal generator is a type of signal generator which outputs predetermined video and/or television oscillation waveforms, and other signals used in the synchronization of television devices and to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses or sync words. Generators of composite video signals will also include a colorburst signal as part of the output.
Analog high-definition television has referred to a variety of analog video broadcast television systems with various display resolutions throughout history.
PAL-M is the analogue colour TV system used in Brazil since early 1972, making it the first South American country to broadcast in colour.
819-line was an analog monochrome TV system developed and used in France as television broadcast resumed after World War II. Transmissions started in 1949 and were active up to 1985, although limited to France, Belgium and Luxembourg. It is associated with CCIR System E and F.
Television standards conversion is the process of changing a television transmission or recording from one video system to another. Converting video between different numbers of lines, frame rates, and color models in video pictures is a complex technical problem. However, the international exchange of television programming makes standards conversion necessary so that video may be viewed in another nation with a differing standard. Typically video is fed into video standards converter which produces a copy according to a different video standard. One of the most common conversions is between the NTSC and PAL standards.
625-line is a late 1940s European analog standard-definition television resolution standard. It consists of a 625-line raster, with 576 lines carrying the visible image at 25 interlaced frames per second. It was eventually adopted by countries using 50 Hz utility frequency as regular TV broadcasts resumed after World War II. With the introduction of color television in the 1960s, it became associated with the PAL and SECAM analog color systems.
525-line is an American standard-definition television resolution used since July 1, 1941, mainly in the context of analog TV broadcast systems. It consists of a 525-line raster, with 480 lines carrying the visible image at 30 interlaced frames per second. It was eventually adopted by countries using 60 Hz utility frequency as TV broadcasts resumed after World War II. With the introduction of color television in the 1950s, it became associated with the NTSC analog color standard.
The EBU colour bars are a television test card used to check if a video signal has been altered by recording or transmission, and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce chrominance and luminance information correctly. The EBU bars are most commonly shown arranged side-by-side in a vertical manner, though some broadcasters – such as TVP in Poland, and Gabon Télévision in Gabon – were known to have aired a horizontal version of the EBU bars.
↑ Lomax, Oliver: The Mood Modern: The story of two of the world's greatest recorded music libraries: KPM (1956-1977) and Bruton Music (1978-1980), Vocalion (2018)
The Test Card Circle, a UK fan site: details of the UK's Trade Test Transmissions including the history of the BBC and ITA Test Cards, a look at the music used and full details about the Trade Test Colour Films shown from the late fifties to 1973.
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