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To many people, computer output means reams of fan-folded paper containing numbers and cryptic messages. The words are generally in one case only ie capital letters, and to read very much of this soon proves irksome. This particular form of output originates from line-printers and still provides for the bulk of directly readable material produced by computers.
Sometimes electro-mechanical graph plotters are used as a means of summarising previously extensive numerical results. Trends in plotted data are readily seen and, of course, objects may be drawn and viewed from different angles. If character sets are made up using lines then both upper and lower case characters, as well as different alphabets, become freely available.
Although reasonably priced, the electro-mechanical graph plotter is not always fast enough to cope with some requirements. Recently, the more expensive Cathode Ray Tube (CRT) terminal has come to the fore. The simple form known as a Visual Display Unit or VDU is somewhat similar to a television set in appearance, but is only capable of displaying numbers and alphabetic characters. These characters are formed by electronic processes on computer command and are then displayed on the face of the CRT. Usually, both case sets are provided for in the 'hardware' or electronics of the terminal.
The full graphics terminal is more elaborate in thet it is also capable of producing lines at any angle and may be activated by using a keyboard and light-pen. The latter is able to detect the displayed data and send signals to the computer as to the location of the 'hit' or detection point. Connected in this manner, whereby electronic signals are transmitted in either direction between computer and terminal, provides for what is known as 'on-line interaction'. The input may optionally be used to modify the output, the changes taking place virtually instantaneously. Alternatively, the computer may be programmed to produce a set sequence of pictures.
These terminals with no mechanical inertia to overcome provide for high speed output. The graphics terminal can display complex drawings in seconds and it is from such a device that cine-films can be made. A camera is positioned in front of the screen (see diagram) and is set off in synchronisation with the picture changes. The general appearance of these films is mainly one of lines, alphabetic characters and symbols on a high proportion, in area, of uniform background. They have more in common with cartoons than of normal or continuous tone, films. The lines and characters may be positioned as the result of highly complex mathematical calculations carried out by the computer, which an ordinary animator would find virtually impossible to match. And it is in this area that computer films are of importance in the teaching and scientific applications field. Artists are also becoming increasingly interested in these products as a means of expression.
Graphic Terminals are not generally suited to quantity production of high quality film output and machines have been specially developed. One such device known as a CRT microfilm recorder manufactured in the USA by Stromberg DatagraphiX is installed at the Science Research Council's Atlas Computer Laboratory, Chilton.
SD-4020 Microfilm Recorder
The microfilm recorder operates from instructions prepared on magnetic tape, produced by programs running on an ICL Atlas computer. In some installations these recorders are connected 'on-line' to the computer, ie connected by information-carrying cables, for immediate response. Standard programs save the user knowing in detail how lines and characters are specified to the recorder. For example, he could draw a cross by punching the following statements on two program cards:
CALL LINE (300, 500, 700, 500) CALL LINE (500,300,500,700)
The commands are then automatically recorded on the magnetic tape in the form required by the recorder. The information is later read from the tape into a buffer store, and after decoding electronically, the electron beam within the CRT traces out the two lines in rapid succession. Pointing at the tube face are either a 16 mm. or 35 mm. camera and a camera containing photo recording paper for enlarged 'hardcopy' prints. In addition to lines, characters formed by extruding the electron beam through an etched matrix can also be displayed and recorded. The aperture setting remains fixed for a particular type of film, and since the CRT and cameras are in a light-tight cabinet the shutters generally remain open during the time a job is running. The time-interval between frame advances varies depending on the information content of the frame or picture. Whilst the film is being advanced under tape command, further display instructionions are held up until the film is again stationary. Typically, lines and points are plotted at the rate of several thousand per second.
To produce a cine-film, the 16mm cine camera is used with black and white negative stock in 400 foot cassettes. It is possible to use colour stock, but as the phosphor of the tube emits light mainly in the blue region of the spectrum, the colours that can be obtained are rather restricted. By making use of a form slide projector, provided for superimposing constant information on the displayed data, but using colour filters, the blue trace may be combined with a coloured background in order to provide colour variations. The addition of a second, different colour filter, replacing the shutter itself allows for further modification in the colours. Opening and closing the now translucent shutter at suitable instants during the production of a frame give two colour plots third background colour.
The black and white film is processed in a small 16mm/35mm table-top microfilm processor at either 3Â½ or 2Â½ feet a minute, but colour film, when used is sent to a commercial film processing laboratory.
Cine-films of any length are readily produced from short sequences by printing from A and B chequerboard rolls which is a method for preventing joins on the print from showing on projection. Some difficulties have been experienced with high contrast prints made on silver stock since the line work is very fine in certain instances. Although Diazo film appears suitable for printing on, at the moment sprocketed feed printers do not seem to be available. This material is exposed to ultra-violet light and processed in ammonia vapour at a speed of approximately 20 feet a minute for this type of work.
In order to retain interest, camera effects such as zooms, wipes, mixes and fades are possible on the displayed objects using suitable computer programs provided for manipulation.
A film made to illustrate the routines available has been produced with a sound-track on magnetic stripe running at 16 frames per second. The professional who made the sound-track did so under protest as the film industry standard is 24 frames per second. However, as computing costs are high, the small drop in quality in this instance with this particular sound track can probably be justified!
The film uses the forms-flash to show a background picture of the Atlas Computer Laboratory with the title of the film - 'FOCUS' - drawn by the microfilm recorder, superimposed. Various routines provided for simulated camera effects and for achieving other necessary functions, such as line-thickening, are shown. Then follows a sequence describing the method used by a contouring routine for handling randomly distributed points having known values. A dramatic view of the earth rotating produced from a program originating from the American Space project, and generated from over eight thousand pairs of numbers representing the coastlines of the world, is accompanied by suitably stirring music. This gives way to a sequence of the British Isles being rapidly drawn as if by hand. The information representing this map contains even more points or pairs of numbers than that used for the whole world in the previous example, giving much greater detail. These values were obtained using a digitiser, a machine that automatically punches out the co-ordinate as a hand-held pen traces the outline. A zoom-in settles on the Atlas Computer Laboratory again and a final 'mix' brings up the word 'END'.
Paul Nelson is a programmer with the Atlas Computer Laboratory. The film 'FOCUS' which is described here was shown at the 1970 British Industrial Film Festival, held at Brighton in June. Copies are available on loan from the ACL Library.