Don
McArthuR's S.A.I.D.
DON McARTHUR
SAID (Spatial and Intensity Digitizer), 1975
Brief: In 1975, at the ETC, with Walter Wright in attendance, Don
McArthur developed the SAID (Spatial and Intensity Digitizer), an
outgrowth of research on the black and white time base corrector.
 |
1938 was the year Donald E. McArthur was born in
Holdrege, Nebraska. He received a Ph.D. in Theoretical
Physics from the University of Nebraska in 1967. After
teaching physics at SUNY in the mid-seventies, he began
designing digital imaging systems for video. His
creations include the Spatial and Intensity Digitizer for
the Experimental Television Center in Binghamton, New
York; and the MeArthur/Schier Digital Image Generator
developed with Jeff Schier for the Vasulkas. McArthur's
interests include heuristic programming, digital
electronics, video systems, and electronic music. |
"As science advances, with the resulting advances in
technology. we have new tools and new capabilities which
influence our world in many ways. This new technology not only
influences the traditional art forms but also produces new forms
of art. The development of high speed electronic components and
cicuits, the cathode ray tube, the video camera, and inexpensive
video tape recorders enabled the development of video art.
Advances in integrated circuit design and fabrication techniques
have led to the development of small but powerful computer
systems which can be utilized by the video artist to achieve a
new dimension of control over the video image. With a
computer-based video svnthcsizer (CBVS), one can generate a
sequence of images while controlling each individual image with
detail and precision that is many orders of magnitude greater
than is possible witb manual control.
The ability to control the dynamics of the image is especially
useful to the artist if the system is capable of generating the
image in real time. With this requirement in mind, the natural
choice of devices for converting electrical signals to visual
images is the conventional video system. This choice also gives
the capability of recording the video compositions with a
conventional video tape recorder and of broadcasting to a large
audience through existing network systems.
There are basically two modes of operation of the system:
interactive-compositional mode and automatic-production mode. In
the compositional mode, the artist can enter programs and
parameters through the keyboard, observe the resulting sequence
of images, and then modify parameters through either the keyboard
or a real time input and thus build up a data set for a complete
piece. The data set, representing all the aesthetic decisions
made by the artist, is stored in the computer at each stage of
the composition. When the composition is finished the system will
operate in the automatic-production mode generating the final
video signal in real time with no intervention by the artist. The
artist may also choose to use a combination of these two modes in
an interactive performance or to allow an audience to interact
with the system operating automatically. The system is structured
so that all of these variations can be accommodated by
appropriate programming.
The system may be operated as a generating synthesizer which
produces a video signal entirely from internal signals or as a
processing synthesizer which utilizes video signals of external
origin such as a camera. Either of these two types of operations
is carried out by a configuration of elements modules, each of
which performs a class of functions, with the specific function
during one frame being determined by the control parameters
received from the computer.
From: "A Computer Based Video Synthesis System"
-Donald E. MacArthur, June 1977
THE SPATIAL AND
INTENSITY DIGITIZER
 |
The "SAID", arose from an early attempt to
create a low cost video speed Analog to Digital converter
(A/D). In 1976 no monolithic silicon A/D converters
existed, and the cost of equivalent industrial modules
was outside the range of most video art budgets. As this
component was basic to digital video processing, a 6 bit
A/D converter was attempted. An A/D converter of 4 bits
or less was commonly constructed using strings of high
speed comparators, but resolutions greater than 4 bits
was difficult to perfect. |
A video A/D converter is built from three main components. A
sample and hold input amplifier, an analog to digital conversion
cinuit, followed by a binary encoding stage to generate a unique
binary number for each of the analog to digital thresholds. The
sample and hold amplifier picks out a sample of the video
voltage, and holds its value until it is fully converted into
digital form. The conversion from an analog voltage to a digital
value is followed by the binary encoder that develops a digital
output as a stream of 6 bit binary numbers, representing 64 video
grey values.
The total conversion time of all elements determines the highest
clock speed possible. The conversion time was slower than
desired, so a horizontally locked oscillator was used to slow
down the clock rate until the conversion was stable. This was
generalized to allow wide variation of oscillator speed to
horizontally sample the image. The output of the A/D converter is
fed to a companion Digital to Analog converter of6 bit
resolution, completing the conversion process from analog to
digital then back to analog.
| The purpose of this circuit is to digitize the video
signal into numerous digital thresholds and then sample
them along the horizontal time axis to create vertical
strips. The spacing or width of the vertical strips of
video is adjustable through an oscillator knob. A switch
to turn off selected digital bits is also available. This
is an early example of the "posterize" function
(bit selection), while the stripes are the horizontal
component of a "mosaic" function, both are
found in digital video effect devices. |
 |
A few words from Woody Vasulka
I think one always remembers the moment of
change of an esthetic norm in one's mind, first the photographic
and film recollections from the memories of others, then our own
experiences with first seeing video and holography. Such a moment
happened to us in, of all places, Binghamton N.Y: looking at a
digital image broken down into the numbers and reassembled again
in real-time. That's how we met Don McArthur and his real-time
digital buffer. In our greed for new images, without even
discussing it, he was hired. A year later, he designed the basic
skeleton of our first true digital image generator. We agreed
with Ralph Hocking on the purchase of his flesh, under condition
that the project would have a binary benefit for both places,
ours in Buffalo and at ETC. The project would mirror all hardware
and software development and Walter Wright would write the first
program.
It only got half way through. Eventually we pulled it through
without ETC by enlisting another character in this drama, Jeffrey
Schier. -W.V.
This page has been largely taken from ARS ELECTRONICA 1992.
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