Indian-head test pattern

A test card for calibration of the RCA TK-1 monoscope.

The Indian-head test pattern is a test card that was introduced in 1939 by RCA of Harrison, New Jersey, for calibration of the RCA TK-1 monoscope. It was widely used by television stations worldwide during the black-and-white television broadcasting era. It features a drawing of a Native American wearing a headdress along with numerous graphic elements that test different display aspects.

As television broadcasting ritual

The Indian-head test pattern became familiar to the large baby-boom TV audiences in America from 1947 onwards; it would often follow the formal television station sign-off after the United States national anthem. The Indian head was also used by the Canadian Broadcasting Corporation (CBC) in Canada in conjunction with its own monochrome test pattern, following the Canadian national anthem sign-off in the evening, and during its final years in the late 1970s and early 1980s, it was shown before sign-on in the morning, after the showing of the SMPTE color bars. It was also used by Rhodesia Television (RTV) during British colonial times (varying between Northern and Southern Rhodesia) following the playing of "God Save the Queen" at closedown. This test pattern was later used by the Venezuelan TV channel Venevision, in conjunction with the RMA Resolution Chart 1941, in the mid and late 1970s before signing on with the Venezuelan national anthem. Telesistema Mexicano (now Televisa) stations also used this test pattern until the late 1960s immediately after playing the Mexican national anthem at sign-off. In Sweden, the Indian head was used in test transmissions from the Royal Institute of Technology alongside the RMA Resolution Chart 1941, Telefunken T05 test card, as well as other experimental test cards from Televerket and Chalmers University of Technology from 1948 until November 1958 when it was replaced by the Sveriges Radio TV (now Sveriges Television) test card. Saudi Broadcasting Authority in Saudi Arabia also formerly used a modified version of the Indian head test pattern, with the Emblem of Saudi Arabia replacing the Indian head drawing, from 1954 until 1982 when it was replaced with a heavily modified Philips PM5544 test card. The Indian head was also used in Brazil by Rede Tupi, both as a test pattern and as part of a television ident, from its launch in 1950 until it became the first Brazilian television network to adopt color television in 1971–1972.

The Indian-head pattern could variously be seen after sign-off but while the station was still transmitting; while transmitting prior to a typical 6 a.m. formal sign-on; or even during the daylight morning hours on newer low-budget stations, which typically began their broadcast day with midday local programming around 10 or 11 a.m.

During the late 1950s the test pattern gradually began to be seen less frequently, after fewer sign-offs, on fewer stations, and for shorter periods in the morning, since new and improved TV broadcast equipment required less adjusting. In later years the test pattern was transmitted for as little as a minute after studio sign-off while the transmitter engineer logged required Federal Communications Commission-US/Industry Canada transmitter readings before cutting power.

By the end of the Indian-head TV era in the late-1970s/early-1980s, there was no nightly test pattern on stations where automatic logging and remote transmitter controls allowed shutdown of power immediately after the formal sign-off. After an immediate transmitter power off, in lieu of the Indian-head test pattern and its sine wave tone, a TV viewer heard a loud audio hiss like FM radio interstation noise and saw the video noise. Audio and video noise received on Indian-head era TV sets respectively indicated the absence of analog aural and visual broadcast carriers. Home-use TVs typically did not have a no-signal noise muting and blanking feature until the late analog TV period.

When US broadcasters switched to color television, the SMPTE color bars largely superseded the black-and-white test pattern image although a few station owners employed colorized versions of the NBC/CBS "bullseye" test pattern, in some cases lasting until as recently as the early 1990s.

Generation

The Indian-head test pattern was not generated by pointing a camera at a card, as many older test patterns were. Rather, it was generated directly as a monochrome video signal by means of a monoscope tube, a specialized video camera tube with the pattern built into the tube.

An RCA TK-1 test pattern generator (monoscope) is a 19-inch rack-mounted chassis, which contains a monoscope tube housed inside an anti-magnetic steel shield and associated electronic circuits for driving it. The monoscope tube is constructed similarly to a small cathode ray tube (CRT), but instead of displaying an image, it scans a built-in image, producing a video signal. The tube has a perfectly proportioned copy of the test pattern master art inside, permanently deposited as a carbon image on an aluminum target plate or slide. This perfect copy allowed all of the television studio and production control room video monitors, and home television sets, to be identically adjusted for minimal distortions such as ovals instead of circles. When the monitor or TV set was correctly adjusted to show test pattern circles, the received picture's aspect ratio was exactly four units wide by three units high.

Use

The graphic of the Indian and all of the patterns on the chart served specific purposes. With the chart, many typical daily (sometimes hourly) adjustments on cameras, home, and studio monitors could be made. An experienced broadcast engineer could glance at the drawing of the Indian Chief and quickly know if everything was working correctly or if the more careful adjustment was needed. Within the chart, the tools necessary to adjust perspective, framing, linearity, frequency response, differential gain, contrast, and white level (brightness) are all provided. The grid and circles were used for perspective, framing, and linearity. The tapered lines (marked with 20, 25, 30, and 35) were used for resolution and frequency response. The thin lines marked from 575 to 325 on one side and 300 to 50 on the other side referred to lines of resolution. The gray bands emerging from the center off to the lower right and upper left were for differential gain, contrast, and white level.

Only after the monitors were adjusted was an actual Indian-head test pattern used. A cardboard-mounted lithograph of the test pattern was typically attached to a rolling vertical easel in each TV studio, to be videographed by each studio camera during test time. Then the cameras were adjusted to appear identical on picture monitors, by alternately switching between and comparing the monoscope image and the test card image. Such adjustments were made on a regular basis because television system electronics then used hot vacuum tubes, the operating characteristics of which drifted throughout each broadcast day.

Test patterns were also broadcast to the public daily to allow regular adjustments by home television set owners and TV shop repair technicians. In this regard, various features in the pattern were included to facilitate focus and contrast settings, and the measurement of resolution. The circular "bullseyes" in the center and the four corners permitted uniform deflection yoke and oscillator amplitude adjustments for centering, pin cushioning, and image size.

The test pattern was usually accompanied by a 1,000 or 400 hertz sine wave test tone, which demonstrated that the TV aural receiver was working. If the tone was pure-sounding rather than a buzz or rattle, then transmitted speech and music would not be distorted. 400 Hz is somewhat less annoying for technicians to hear for extended work periods.

As a cultural icon

An actual Indian-head test card, the pattern as printed on art-grade white cardboard, was only of secondary importance to television system adjustment, but many of them were saved as souvenirs, works of found object art, and inadvertent mandalas. By contrast, nearly all of the hard-to-open, steel-shielded, vacuum glass monoscope tubes were junked with their hidden Indian-head test pattern target plates still inside. The monoscope target plates were also small, a few inches in size, while the camera test cards were 1.5 by 2 feet (0.46 by 0.61 m), appropriate for picture-framed wall display.

The original artwork for the Indian chief portrait was completed for RCA's research engineers by an artist named Brooks on August 23, 1938. The original portrait was done in pencil, charcoal, ink, and zinc oxide. For about a year the Indian portrait was televised in the laboratory as the entire test pattern. It was later incorporated into the pattern of calibrated lines and shapes. The original portrait measures eight inches (20 cm) across as a circular image containing several identifiable shades of gray, and some detail in the feathers. There is also some Zone 8 texture in the white feathering and some Zone 2 texture in the black hair. The master art for both the portrait and the pattern design was discovered in a dumpster by a wrecking crew worker as the old RCA factory in Harrison, New Jersey was being demolished in 1970. The worker kept the art for over 30 years before selling it to television engineer and collector Chuck Pharis.

The Indian-head test pattern became obsolete in the 1960s with the debut of color television; from that point onward, an alternate test card of color bars became the test card of choice. Since the 1990s, most television stations in the United States have broadcast continuously without regular sign-offs, instead of running infomercials, networked overnight news shows, syndicated reruns, cartoons, or old movies; thus, the broadcast of test patterns has become mostly obsolete (though they are still used in post-production and broadcast facilities to check color and signal paths). Nevertheless, the Indian-head test pattern persists as a symbol of early television. A variant of the card appeared on theatrical release posters for "Weird Al" Yankovic's 1989 film UHF. It was sold as a night-light from 1997 to 2005 by the Archie McPhee company, reminiscent of the times when a fairly common late-night experience was to fall asleep while watching the late movie, only to awaken to the characteristic sine wave tone accompanying the Indian-head test pattern on a black-and-white TV screen. The test card also featured in the opening sequence of the early 1960s science fiction anthology The Outer Limits. Decades later, it was popularized as the loading screen for the Fallout series video games, and a part of the Electronic Frontier Foundation's website.

Many U.S. television stations chose the image of the Indian-head card to be their final image broadcast when their analog signals signed off for the final time between February 17 and June 12, 2009, as part of the United States digital television transition.

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Indian-head test pattern
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Adapted from content published on wikipedia.org
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  • Image By Alex Microbe - This file was derived from: RCA Indian Head test pattern.png, Public Domain — from wikimedia.org
Last modified on May 25, 2021, 6:49 am
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