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Multi-Level Keyer (Multikeyer)

Multikeyer, Technical drawing (ca. 1977)
Tool Identification

Name of tool: Multi-Level Keyer
Alternate name: Multikeyer (analog with digital control)
Inventor/Designer: George Brown
Date of design: 1973

Historical notice

The Multi-Level Keyer was designed and built by George Brown in 1973 at the request of videomakers Steina and Woody Vasulka who wanted a sophisticated keyer that would exceed the two-level input that this type of device allowed in the early seventies (see Operating Mode). A computer interface was added in 1977 to simplify the control, storing and triggering of programmed sequences (see Operating Mode). The Vasulkas still have one copy at their residence in Santa Fe (U.S.).

Description of the tool

The Multi-Level Keyer consists of two boxes on a processing rack. The first contains the digital components (sequencer, encoder, programming interface), while the second includes the analog components (mixing units and keyers).

Brief list of materials

Modules of electronic and digital components on a processing rack.

List of components

Digital sequencer with encoder; programming interface; diode display; clock; integrated analog mixers and keyers.

Operating mode

The Multi-Level Keyer is a hybrid luminance keyer (analog and digital) designed to program and display in real time the keying sequence of video sources in one image plane. Luminance keyers from the early seventies created a stacking of video sources by replacing a section of the image with a new value. These keyers could receive only two signals at a time. Superposition of a third source was possible through the recording of a first effect on magnetic tape (producing multi-generation tape loops and poorer image resolution quality). The Multi-Level Keyer is equipped with five points of entry and six planes for processing the video sources (camera, magnetic tape reader, etc.) to faithfully restore the output signal. The digital sequence with encoder of the Multi-Level Keyer controls two parameters of the luminance keying process: the hierarchy in the display of the image planes and the length of display. The sixth source acts as a ground on which the five image planes are stacked. Combined with the other components of the Multi-Level Keyer, the sequencer creates a scale of 16 steps or states that control the two keying parameters for each video source. The sources are encoded, and the encoding data are stored temporarily in a memory unit before the sequence is displayed on the monitor. A programming interface, outfitted with a board similar to a telephone pad, can program the display parameters of the planes. This interface is equipped with a diode display where users can view operations underway when the image is displayed on a monitor. A clock acts as a link between the programmed parameters and the analog components. The integrated analog keyers and mixers feature potentiometers controlling other display parameters like the contrast and brightness. The Multi-Level Keyer can also support a computer interface to more effectively control, store and replay the keying sequences using digital code.

Effects

Keying; programming key priorities.

Consulted documents 

George Brown : video multikeyer. — [ca 1985]. — [24] p. — Diagrams / Technical drawings. — Included in the file entitled "Brown, George". 

Schier, Jeffy. — George Brown : Multi-level keyer. — April 21, 1992. — 2 p. — Technical description. — Included in the file entitled "Brown, George". 

Vasulka, Woody ; Vasulka, Steina. — Eigenwelt der Apparatewelt : Pioniere der Elektronischen Kunst = Pioneers of electronic art. — Artistic direction by Peter Weibel, edited by David Dunn. — Santa Fe : The Vasulkas ; Linz : Ars Electronica Center, 1992. — 240 p. Also available on the Internet : http://www.vasulka.org/Kitchen/PDF_Eigenwelt/Eigenwelt.htm [ref. September 23, 2003].