Indian-head test pattern
The Indian-head test pattern was a black and white television test pattern which was introduced in 1939 by RCA of Harrison, New Jersey as a part of the RCA TK-1 monoscope. Its name comes from the original art of a Native American featured on the card.
As television broadcasting ritual
The Indian-head test pattern became familiar to the large Post–World War II 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 in Canada, following the Canadian national anthem sign-off in the evening. It was also used by Rhodesia Television (RTV) during British colonial times (varying between Northern and Southern Rhodesia), as the pattern was displayed following the playing of God Save the Queen. This test pattern was later used by Venezuelan TV channel Venevision, in conjunction with the RMA Resolution Chart 1941, in the mid and late 1970s before the Venezuelan anthem (Gloria al bravo pueblo). Telesistema Mexicano (now Televisa) stations also used this test pattern until the late-1960s immediately after a Mexican National Anthem (Mexicanos, al grito de guerra) film. In Sweden the Indian head was used in test transmissions from the Royal Institute of Technology from 1948 until November 1958 when it was replaced by the Sveriges Television test card.
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 AM 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 AM.
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-USA/Industry Canada transmitter readings, and then turned off the power.
Towards the end of the Indian-head TV era (around the late 1970s), there was no nightly test pattern on some stations, typically when 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 colloquially called snow (but resembling "bugs" following a TV-system technical improvement). Audio and video noise received on Indian-head era TV sets respectively indicated the absence of analog aural and visual broadcast carriers. Consumer TVs typically did not have a no-signal noise muting and blanking feature until the late analog TV period.
As television system tool
The primary and critical Indian-head test pattern was not itself a card. Rather, it was generated directly as a monochrome video signal by means of a monoscope camera.
An RCA TK-1 test pattern generator (monoscope) is a 19-inch rack-mounted chassis, which contains electronic circuits needed to operate a glass cathode ray tube housed inside an anti-magnetic steel shield. The cathode ray component is a TV-camera vacuum tube known as a monoscope, because it videographs only one still image, the test pattern. 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 minimum 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. The 4 by 3 standard was chosen by the National Television System Committee (NTSC) for analog television, so that film movies would be compatible with TV broadcasting. 4:3 is the same aspect ratio used by 16mm and classic 35mm motion picture film frames.
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 OK or if 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 "bulls-eyes" in the centre and the four corners permitted uniform deflection yoke and oscillator amplitude adjustments for centering, pincushioning, and image size.
The test pattern was usually accompanied by a 1,000 or 440 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. 440 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 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 showy camera test cards were sized on the order of 1-½ feet by 2 feet, making them natural keepers for picture-framed wall display.
The original art work was completed for RCA by an artist named Brooks on August 23, 1938. The master art was improbably discovered in a dumpster by a wrecking crew worker as the old RCA factory in Harrison, NJ was being demolished in 1970. The worker kept the art for over 30 years, and then used the Internet to locate and sell it to a test pattern collector.
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 running infomercials, networked overnight news shows, syndicated TV re-runs, or old movies; thus, all test cards have become mostly obsolete. 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 UHF (film). It was even 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 had also featured (during its own heyday) in the opening sequence of the early 1960's science fiction anthology The Outer Limits.. It is also the first loading screen for the video game Fallout 3..
Many of the nation's television stations used the image of the Indian-head card to be their final image broadcast when they signed off their analog signals for the final time between February 17 and June 12, 2009, as part of the United States digital television transition.
- Kay, M. S. (January 1949). "The Television Test Pattern". Radio & Television News (Ziff-Davis) 41 (1): pp. 38–39, 135–136. "Every television station, prior to its actual broadcasting period, transmits a test pattern for the purpose of permitting set owners to adjust their receiver controls for optimum reception." The article also states that television programming (in 1949) was only a few hours each evening. The Indian-head test pattern was built into the RCA "monoscope" tube, a 2F21, which acted as a complete replacement for the TV camera.
- TV/video "snow" noise is unrelated to "White noise". TV "snow" vaguely resembled precipitating snow at night (in the UK, anyway). White noise is an analogy to the flat-amplitude continuous-frequency spectrum of white light, as opposed to pink noise that gradually increases in strength toward the red or bass end of the audio frequency spectrum.
- This video noise resembles fast-flickering white snow precipitation on a black background on TV systems which use positive video modulation, however views of systems using negative modulation (such as NTSC TV-system viewers in the USA, Canada, and Japan) saw an impression of fast-flickering black "bugs" on a white background. The NTSC committee chose negative video modulation, because flecks of white "snow" are more noticeable and annoying than flecks of black "bugs".
- The target plate is sequentially scanned with a focused beam of electrons, which were originally called cathode rays. When the electron beam strikes the carbon image areas, the carbon resists current flow, and the resulting lower electron current flow is adjusted to appear as video black. When the electron beam strikes the metallic-aluminum image areas, there is less resistance with higher current flow, and the resulting higher electron current flow is adjusted to appear as video white.
- Not including Cinemascope 35mm anamorphic wide-screen film frames, both wide screen sides of which were unseen on TV prior to the later analog TV practice of letterboxing wide screen films. Occasionally, anamorphic films were locally broadcast in error using a standard, non-anamorphic film chain lens, resulting in the TV viewer seeing tall, thin El Greco-effect people, squeezed more in the center than at the top and bottom. Also, the El Greco effect was unavoidable while showing the film credits, as wide-screen words on either side would otherwise not be visible; not showing readable credits would typically be a movie-broadcasting contract violation.
- The analog TV monaural audio transmission was nearly identical to analog monaural FM radio. Automobile drivers in USA cities with a TV channel 6 could listen to channel 6 audio at 87.75 MHz, just below the lower end of the FM radio broadcast band at 87.9 MHz. The two systems of transmitting stereo were completely different.
- 1,000 Hz is the standard 0dB (0 decibel) reference point for analog-NTSC TV aural system frequency response measurements, but for simple line-reference 0dB audio level setting, preference for hearing 440 Hz is common knowledge and experience among broadcast and audio technicians. "From the factory the frequency of the reference tone is configured to be 440 Hz. This is a nice alternative to the more typical 1 kHz, a frequency which can soon become very annoying to a listener’s ears. In most cases 440 Hz will be perfectly acceptable, and actually preferred." - Model 742 Audio Mixer User Guide, Issue 2, May 2005 (PDF); p.10 - Studio Technologies, Inc.
- The Indian-head test pattern night light was included in a set of three novelty night lights with test pattern lamp shades: RCA TK-1 Indian head (1950s), SMPTE color bars (1960s), and an Emergency Broadcast System (EBS) TV-test slide image ("This is a test! This is only a test!") from the middle Cold War era. Each of the three images were printed on 3" x 4-½" paper, and mounted in a clear plastic cover within a curved, TV-screen-styled clip-on white plastic frame. Each translucent image was rear-illuminated by a 4-watt incandescent bulb. The candelabra screw (E10, Edison screw, 10 mm) bulb was part of a standard plug-lamp-and-switch night light, fitted with a North American 120v, ½" parallel-prong, to be left indefinitely plugged into a USA household duplex electric outlet. According to the customer service department of Archie McPhee company, Seattle, Washington, the set of three, as Item #10480, was sold from 1999-01-11 to 2005-06-17. Their representative said these lamp shades were created by the company, and not obtained from an outside source. (Source accessed by phone on 2007-11-07). The images were labeled "1998 Accoutrements". According to the Accoutrements LLC website, Archie McPhee is their company's retail division.
- The Indian Head Test Pattern original master art – rescued from an RCA dumpster in 1970
- Picture and detailed description of an RCA TK-1 test pattern generator (monoscope)
- mire.project – Street art work about test patterns