Editing Indian-head test pattern (section)

== Features and use ==
[[File:Radio TV News Jan 1949 pg38.jpg|thumb|The Indian Head pattern as mentioned in [[Ziff Davis]]'s ''Radio & Television News'' trade magazine in January 1949.]]
[[Image:Indian Head Test Pattern with Labels.png|thumb|upright=2|Indian Head pattern with its elements labeled, describing the use of each element in aligning a black and white analog TV receiver.]]

The Indian-head test pattern was created by [[RCA]] at their factory in [[Harrison, New Jersey]]. Each element of the card was designed to measure a specific technical aspect of television broadcast so that an experienced engineer could, at a glance, identify problems. The card contains elements used to measure aspect ratio,{{efn|[[Analog television]] on [[cathode-ray tube]]s also needed to be adjusted for vertical and horizontal linearity. An error in vertical linearity (such as the top of the picture stretched with the bottom squashed) might go unnoticed on the SMPTE colour bar pattern, but would instantly turn a circle into an egg-shape.}} perspective, framing, linearity, frequency response, differential gain, contrast, and brightness. 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.

The pattern began with the Indian-head portrait created in August 1938 by an artist named Brooks using pencil, charcoal, ink and [[zinc oxide]].<ref name="Pharis" /> For about a year, the portrait (which contains several identifiable shades of gray from [[Zone System|Zone VIII]] texture in the white feathers to [[Zone System|Zone II]] texture in the black hair) was the entire test pattern, but in 1939 the portrait was incorporated into the current pattern of calibrated lines and shapes.

[[File:RCA TK-1C.jpg|thumb|The RCA TK-1C monoscope camera that generated the test pattern]]Television stations would produce the image of the Indian-head test pattern in two ways. First, they would use a [[monoscope]] in which the pattern was permanently embedded, which was capable of producing the image with a high degree of consistency due to the device's simplicity. 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 (or a modified variant with the station ID replacing the Indian-head portrait, such as those used by [[KDFW|KRLD-TV]],<ref>{{cite web | url=https://www.earlytelevision.org/rca_tk1c.html | title=RCA TK-1C Monoscope}}</ref> [[KXAS-TV|WBAP-TV]]<ref>{{cite web | url=https://digital.library.unt.edu/ark:/67531/metadc1337921/ | title=&#91;WBAP-TV Test Pattern&#93; | date=1965}}</ref> and [[KFOR-TV|WKY-TV]]<ref>{{cite web | url=https://www.tahlequahdailypress.com/news/tv-transformative-for-tahlequah-residents/article_1f190770-f861-5b79-a644-f025201f2e64.html | title=TV transformative for Tahlequah residents | date=8 October 2016}}</ref>) inside, permanently deposited as a carbon image on an aluminum target plate or slide. 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. This image was used to calibrate monitors in the station. Second, stations would use a cardboard-mounted lithograph of the test pattern (typically attached to a rolling easel in each TV studio); videographing the lithograph would create a second image that could be compared against the monoscope-created control image.

The test pattern was useful for the calibration of home television sets as well as television studio equipment, so the image was routinely broadcast outside hours of [[Broadcast programming|programming]].<ref name="RTVN1949">{{cite journal | last = Kay | first = M. S. |url=https://commons.wikimedia.org/wiki/File:Radio_TV_News_Jan_1949_pg38.jpg |title=The Television Test Pattern | journal = Radio & Television News | volume = 41 | issue = 1 | pages =38–39, 135–136 | publisher = Ziff-Davis |date=January 1949 |format=scan |via=Wikimedia}} "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 program]]ming (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.</ref> (It was often accompanied by an audio test tone for the purposes of calibrating aural system frequency response measurements.<ref>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 400 Hz is common knowledge and experience among broadcast and audio technicians. "From the factory the frequency of the reference tone is configured to be 400 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 400 Hz will be perfectly acceptable, and actually preferred." - [http://www.studio-tech.com/PDFFiles/M742ug_2.pdf Model 742 Audio Mixer User Guide, Issue 2, May 2005 (PDF)] {{webarchive|url=https://web.archive.org/web/20061217022352/http://www.studio-tech.com/PDFFiles/M742ug_2.pdf |date=2006-12-17}}; p.10 - Studio Technologies, Inc.</ref>)