Computer Animation

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J. Halas

Computer animation
This paper on computer animation is based on a presentation by the author to the Royal Television Society in September 1 970. The history of the use of computers by the animation industry is traced and examples given of programs used for various processes in making animated films.

For thirty years nothing much happened in animation technology until the beginning of 1964, when Dr. Edward Zajac and Ken Knowlton, together with their assistants at Bell Telephone Laboratories in New Jersey, U.S.A., developed a technique to produce computer made animated films. The spread of the technique is reminiscent of three periods in the history of visual communication. The first the rapid development throughout the world of motion picture production in the middle twenties - the second the rapid development of television technology after the war. The third - the invention of the 16 and 8 ram. cameras after the war which opened up the field to specialised and amateur cinematography. By the nineteen sixties the computer proved to be a highly adaptable tool for industry, commerce, education and science. Its versatility allows it to be used in many ways, to solve a varied range of tasks at a speed and precision no human being is able to achieve. Among these tasks is the computer's ability to create moving images. The system, which demands a complete departure from the conventional form of film making has so far depended on a numerical breakdown of the visual images in mathematical terms in order to define the precise shape, size, time, direction and velocity of any movement. In spite of the fact that the computer has proved to be the most intelligent machine ever thought of, it still must be told what to do, and since the F O R T R A N language was already in existence, it was the most obvious language which could be adapted for animation. While in the United States several langu~,ges have been evolved to a highly sophisticated level, in this country there was a necessity to pioneer, in many cases right from the beginning. During the last few years the National Computing Centre has kindly undertaken to carry out some experiments in animation, and so has the Department of Computer Sciences at the Computer-Aided Design Project, University of Edinburgh. Both organisations carried out this work in association with Halas & Batchelor Animation Ltd. In addition to these, the Atlas Computer Laboratory in Chilton, Didcot, backed by the Science Research Council, has produced animation devised by Mr. Paul Nelson for B.B.C.-tv.

National Computing Centre
Dr. F. E. Taylor and Mr. Maurice Russoff have produced an experimental film as a part of Halas & Batchelor's educational geometry series entitled Pole and Polar. Dr. Taylor and Mr. Russoff describe the application of the technique as follows: "Films can be produced using computer assistance in one of two ways: (a) by using a pen type plotter to draw the required diagram, and subsequently filming this, or (b) using a special purpose device - in particular the Stromberg Carlson 4020 or 4060 plotter, or its equivalent, available from other companies, producing records on film directly. Further, the computer can be used in three ways to produce 'animated' films: (a) simply as a drawing aid for the production of diagrams built up from regular geometrical figures, or figures capable of mathematical description. Only a small number of 'strategic' drawings need to be programmed - these sub-programs can then be called at will to produce combinations of such figures. (b) this scheme can be extended by allowing the production of films which are animated in three dimensions - i.e. the sub-programs already mentioned above, corresponding to particular figures have an added facility which allows them to be rotated and thrown into perspective, to give the effect of a third dimension. (c) films representing given mathematical functions, normally time-dependent functions such as the dam collapse, can be produced using the mathematical equations describing such a phenomenon as a basis.

Action Taken
So far as the U.K. is concerned, it was decided to concentrate on the educational area for the time being, and to undertake experimental work combining techniques (b) and (c) above - i.e. producing a film for educational use which involves handling two-dimensional figures which are rotated - i.e. effectively have three dimensions, the figures themselves being mathematically definable curves. Programming work was undertaken at the National

Computing Centre, but all programs generated were run on the Atlas II/SC4060 system at Aldermaston, so that the system software already existing at that establishment for the SC plotter could be used as a basis. This report details in turn: - the 'storyboard' chosen, - the techniques used - hardware and software, - operational aspects of the experiment, - t h e economics resulting, with a comment on future economics and future plans. In connection with economic considerations, it was decided to attempt to ascertain just how much faster films could be prepared, using computer assistance, and how much manpower requirements were reduced, by eliminating a great deal of tedious manual drafting.
Commercial Exploitation of this Technique

continuous loop mounted in a cartridge which may be placed into a slot. No complicated threading of the film or rewinding is required.

The Storyboard Chosen
The conventional way of producing animated films is to draw and then expose the film frame by frame. If the film content is mathematical, then elaborate calculations must be performed before any particular frame can be drawn. On occasion, the necessary calculation may be so long and laborious as to preclude attempting to produce such a film using conventional techniques. It is in this situation that computerised animated techniques score over conventional methods. The calculating power of the computer can be used to determine the state of a particular motion sequence frame by frame, and using the microfilm and recorder described above, eliminates even the necessity to draw up and then film these frames. The storyboard of the film produced during this feasibility study (see Fig. l) is of a precise geometrical nature that would enable it to be produced fairly easily by conventional techniques, but also involves sufficient mathematical calculation to render it suitable for computerised animation, thus enabling a direct comparison to be made between the effort and costs involved in both manual and computer production methods. One can envisage other subjects, e.g. moving lines of force fields around magnetic poles, which involve a lot of calculation to describe them and which are not precisely defined geometric shapes that are easily drawn using a compass and ruler. In this case, computerised animation would be the better and possibly only method of producing the film. Again, there are other subjects with little or no mathematical content which are better animated using conventional techniques. There is another benefit from using computerised techniques. The programs to produce the film are written in a general form and it is only at 'run time', when the magnetic tape for driving the microfilm recorder is being written, that the actual co-ordinate positioning information of the figures in the film need be specified. This means that after producing one 'take' if the size or shape of an item is to be altered, the program can be simply run again with new co-ordinate data to produce the next 'take'. Using conventional methods, the whole film would have to be recast or redrawn frame by frame to incorporate such changes, whereas precise positions can be specified very quickly using computer techniques. In this case, it was decided to produce a short film titled Pole and Polar. The basic construction illustrated by the film is shown in the storyboard diagram (Fig. 1). The sequence is first constructed for a circle and then repeated for an ellipse. Finally, keeping the lines VU, VS fixed, the ellipse is gradually changed into a circle and then back to an ellipse again, to illustrate the general nature of the construction. The sequences are interspersed with titling, which has also been produced automatically on the microfilm recorder.

This report describes the pilot study undertaken by the National Computing Centre Ltd. in conjunction with Halas & Batchelor Animation Ltd., aimed at production of a film suitable for teaching the mathematical concepts associated with the pole and polar of a conic section - in this case an ellipse. The incremental cost of producing further films, once the techniques are established, is discussed later. The objective is to produce films for screening on small back-projection monitor units, resembling a television receiver, available to teacher and pupils in a classroom. The final film is to be in 8 mm. form and is made up as a

~5 This line is the with of the point " pole V 1 respect to V

Circle growsto full size t~6
/i /I I

Linestangentsto circle~









Fig, 1. 30

Repeat for ellipse

Techniques Used

The method makes use of a MICROFILM RECORDER, details of which are shown in Figs. 2 and 3. As shown in the diagram of the optical system of such a recorder, a precision cathode ray tube is situated optically in front of two cameras, one of which will expose 35 mm.

Mf c ~~ ~ c 0~ m m. o ri ,i i r

2. Fig. 4

Control electronics


Fig. 3.

ardcopy camera Cathode roy tube

MICROFILM RECORDER Over I million oCldressoblepoints Face of cothoOe roy tube


Fig. 4.

~ ~i ¸!!!iii!!ji~i~i
Read and set 'Mod~/Frames" and any coordinate data

J Set 'Count' = 1 ~

Advance frame on c a m e r a specified by "Mode'

ca,oo,o,2 oor;i"ates for

current frame using "Count" I as a variable parameter / J



to 'draw' straight line vectors between any two of these points. In this way, pictures can be built up from such vectors, and as each vector is displayed it will be recorded on the frame of film or paper currently in position. When the complete picture has been built up, another 'frame advance' command is given and the next frame will be brought into position ready to be exposed. The microfilm recorder is driven by information read from a magnetic tape. Such tape contains 'frame advance' commands as well as co-ordinate information associated with 'expose' commands. It is prepared by using a computer for which a program package capable of generating commands to drive the microfilm recorder, has been written. In this case programs are written in a dialect of FORTRAN 2 for running on an ICT Atlas 2 computer. The microfilm recorder is a Stromberg-Carlson SC 4060 operated as a SC 4020. The latter is an earlier model for which the necessary program package is available. The equipment used was that at A.W.R.E., Aldermaston.



I Add 1 to-Count

microfilm, whilst the other produces hard copy output on photographic paper. Either or both cameras can be chosen automatically by program commands. The complete optical system is housed in a light proof enclosure and the camera shutter mechanisms are held open all the time. The film or photographic paper is advanced by program commands, during which time the face of the cathode ray tube is automatically blanked off. When the new frame of film or paper is in position, the control electronics then expose that frame by displaying graphic information serially, once only, on the face of the cathode ray tube. The positioning of this information on the face of the tube is defined by a 1024 x 1024 matrix of addressable points and the electron beam can be deflected

The software used consists of a MAIN program, which calls several system and user-generated SUB-PROGRAMS. (a) Main Program The structure of the main program of a film is shown in the flowchart - Fig. 4, where three 'names' are mentioned. The function of these names is as follows: 1. M O D E - this will appear in a F O R T R A N statement at stage 3 as CALL ADVFLM (MODE) If MODE is set : (a) equal to 1 (at stage 1) the microfilm camera will be selected and advance, or (b) if set equal to 2, the hard copy camera will be similarly activated. It is useful when program testing and debugging, to produce a few frames of paper output first of all and then if all is well, run the program again with the microfilm camera selected.



2. F R A M E S - in general a s t o r y b o a r d will consist of a sequence of 'scenes' each of which can be described at Stage 4. T h u s the m a i n p r o g r a m flowchart in general will represent the filming of one of these scenes, a n d the variable F R A M E S will d e t e r m i n e the n u m b e r o f frames of film p r o d u c e d for t h a t scene. F o r 35 mm. film, the projection rate is 24 frames per second, a n d F R A M E S will d e t e r m i n e how long the scene will last when projected. It is possible to film successive scenes by linking together a n u m b e r of main p r o g r a m segments.
- this variable is i n c r e m e n t e d every time a frame is p r o d u c e d (Stage 6) a n d is used to d e t e r m i n e when the scene has been c o m p l e t e d (e.g. C O U N T = F R A M E S ) . C O U N T is also used in Stage 4 to calculate the intermediate c o - o r d i n a t e values of figures t h a t are ' m o v i n g ' d u r i n g the scene. If, say, the e n d of a line C is to swing between two points A a n d B, then the X c o - o r d i n a t e of the end of the line d u r i n g the scene is (X ,Y ) given by: X = XA + (XB XA) B *COUNT/FRAMES 3. COUNT


Direction of travel In projector



procket hole



X= 1023~,

W h e n C O U N T = F R A M E S , X = XB. C O U N T is initialised at Stage 2. Stage 5 Details (see Flowchart - Fig. 4) T h e interface between the user's F O R T R A N p r o g r a m a n d microfilm recorder is a p r o g r a m package w h i c h includes s u b r o u t i n e s t h a t can be i n c o r p o r a t e d in the user's p r o g r a m s a n d will, as a result, p r o d u c e a magnetic tape o u t p u t written in a f o r m a t suitable for driving the recorder. T h e basic s u b r o u t i n e p r o v i d e d in this way is V E C T O R . This will a p p e a r in a F O R T R A N p r o g r a m as: CALL VECTOR(XI, YI, X2, Y2)

--Stripchort orientotion~




Fig. 5.

If an imaginary Cartesian c o - o r d i n a t e system is assumed on the face of the c a t h o d e ray tube, then this s t a t e m e n t causes the electron b e a m to Face of tube be m o m e n t a r i l y deflected bet w e e n t h e points (X1, Y1) a n d (X2, Y2), thus p r o d u c i n g the line on film or paper. T h e o r i e n t a t i o n o f the axes with respect to the film is given later. As explained earlier, the addressable points a r e a r r a n g e d as a 1024 x 1024 matrix so t h a t the variable p a r a m e t e r s specified with the V E C T O R s u b r o u t i n e should be restricted to : (X) 0.0 % ( y ) ~-~- 1023.0 These p a r a m e t e r s in F O R T R A N s h o u l d be real variables (i.e. should not begin with the letters 1, J, K, L, M o r N ) but since the fractional values have no meaning, it is as well to t r u n c a t e the fractional part. F o r example, if X C O R D I is a variable within the user's p r o g r a m , a statement such as:

s h o u l d appear, XI a n d n o t X C O R D 1 a p p e a r i n g in the V E C T O R s u b r o u t i n e statement. If X C O R D 1 = 241'385, then the value inside the bracket will be 241.885 a n d X I will be assigned the real value 241.0 ( I N T F is a s t a n d a r d F O R T R A N s u b r o u t i n e which takes the integer value of the c o n t e n t s of the brackets which follow it). As s h o w n in Fig. 5, the o r i e n t a t i o n of the c o - o r d i n a t e system on the film when the basic V E C T O R s u b r o u t i n e is used is with the positive X axes a l o n g the film. Since for a n i m a t i o n , the pictures o n successive frames must a p p e a r one b e n e a t h the o t h e r o n the film (and not o n e next to the other), a n d also since it is m o r e c o n v e n i e n t to t h i n k of the X a x i s as horizontal a n d the Yaxis as vertical, a c o - o r d i n a t e t r a n s f o r m a t i o n is m a d e to re-orientate the axes suitable for stripchart or movie film. This re-orientation is o b t a i n e d by writing V E C T O R statements as: C A L L V E C T O R ( YI, 1023.0 X1, Y2, 1023.0 X2)

+ 0"5)

It may also be necessary to ask the o p e r a t o r to set the microfilm recorder to 'strip c h a r t ' mode, so t h a t a frame is p r o d u c e d every fifth sprocket hole. In the 'microfilm' m a d e it is usual to p r o d u c e a frame every seventh hole. The area o n the film over which the microfilm recorder can expose graphic i n f o r m a t i o n , does n o t c o r r e s p o n d to the s t a n d a r d 35 ram. image area (see Fig. 6). In order to expose only that part of the microfilm recorder frame t h a t corresCOMPUTER AIDED DESIGN


ponds to the standard 35 ram. image area, a further restriction is placed on the co-ordinate values allowed. This restriction is: 0.0 0-0 X Y 1023.0 818.0

This ore° is projected on the screen, but no plotting con occur within it

This area is known as the working area. Also due to the presence of a sound track on standard 35 mm. film, the central point of the projected area does not correspond to the central point of the working area. To obtain pictures centrally on the screen, these pictures should be centred about the point: X = 579"0 Y = 384-0

A drafting template is shown which can be used to plan out the graphic information and to determine any coordinated data that is required. (See Fig. 7.)


Operational A s p e c t s
General This summarises some of the problems encountered in producing the film. Some of these have already been detailed.

Fig. 7

D o not plot in this ore°, (Is it is not projected on the screen.

There are five main stages in the commercial production of films, pursuing the techniques described in this report. These are: (a) choice of suitable storyboard subjects; (b) detailed specification of the storyboard so that the general programs can be written; (c) writing the programs and debugging by computer runs using the hard copy camera; (d) computer runs with suitable data to produce the final film; (e) final processing and editing of the film.

This work will, in general, be split between the film maker and the systems analyst/programmer, and as in all other computing activities it is important that each appreciates the other's needs and has sufficient information to correctly carry out his part of the work. In particular, the film maker must appreciate the criteria for choosing suitable storyboards and must then be able to hand over a detailed storyboard. Information such as image positioning and size, and the timing of the various sequencies, is not needed until Stage d, when this information can be read in at computer 'run-time'.

Software Difficulties
Each category of storyboard subject will require a number of special subroutines to be written. The main subroutines written for the film described in this report are JOIN, ELLIPS and ELLCUT. The difficulties met in writing these subroutines were as follows: (a) JOIN - this subroutine was written to ensure that only co-ordinate values that lie within the 1024 x 1024 matrix of addressable points are specified with the systems subroutine VECTOR. The effect of using VECTOR with co-ordinate values outside this matrix is undefined and in any case will vary with different plotting systems. With
X=1023 i


Direction of trovel in projector

Light being projected




y----8 y~lo -I-.


,mo0e oreo pro, eotod


Fig. 6. SPRING 1971

the system software supplied for the SC 4060 spurious outputs of the part of the line outside the addressable region can be obtained. The only other difficulty with JOIN is to ensure that all possible cases of the positioning of the two

points with respect to the working area, are catered for. These include both points inside the area, one point outside the area and both outside the area. In the latter case the line joining the two points may not, in fact, cut across the working area. (b) ELLIPS - with a close figure such as an ellipse or circle, that can vary in size, the length of the individual vectors that make up the figure is important. This subroutine is written so that the length of these vectors will change according to the size of the figure, but even so there is a limit to how small a figure the subroutine can be used to draw. The individual vectors become most prominent in the areas of high curvature which will occur at the possible apices of the ellipse depending on its


The numerical method of solution, as in the other method, gives an accurate answer. Accuracy is particularly important in this case, as described in the next section. MAIN P R O G R A M - the major difficulty in writing the main program is to ensure that the coding written produces the required graphical output for all possible variations in co-ordinate positioning, and also that any peculiar situations that may occur through such a sequence are appreciated and allowed for in the program. For example, if the construction shown in diagram (a) of Fig. 8 is made to move by rotating the line VU in the direction indicated, the point W will move out of the right hand side of the picture and reappear from the left. Also as shown in diagram (c), the line VU may lie on top of the line VS so that the points A and B and the points C and D coincide. The program must test for such conditions and take appropriate action (in this case, possibly by missing out the frame altogether).

Regions where smaller v e c t o r lengths used


orientation. For this reason, a smaller vector length is used in the regions indicated in the diagram. However, it should be noted that attempts to improve the quality of the figure (by reducing the vector length in this way may be thwarted by the repeatability properties of the plotter itself). Each vector drawn by the plotter will not quite mate up with the end of the previous one, and this effect is most marked the greater the vector density. Factors limiting the repeatability performance of a plotter will include the following: 1. Any movement of the film caused by mechanical instabilities. 2. Drifting of the electronics due to temperature and voltage variations. 3. Distortion introduced by the optical system. 4. Drifting of the optical system due to temperature variations. 5. The positional accuracy of the cathode ray tube. E L L C U T - the function of this subroutine is basically the solution of the two simultaneous equations describing the ellipse and straight line. These are:





Fig. 8




ix XCENTI2 ir YCENTI 2 ~ - S - - E M ~ ~' + '~ SEMMIN I = 1 . . . . (1) X XI Y Yl
Y2 . . . . (2)

~ W

Line - XI -- X~2- YI -

Elimination of either variable leaves a quadratic m the other to be solved. This method of solution to obtain the points of intersection of the line and ellipse was abandoned in favour of another method, because the numbers involved quickly overflow the range of numbers permitted by the computer, and in any case the solution of a quadratic may involve the subtraction of quantities which unless they can be specified with high precision, will result in errors in the answer.







Note that such peculiarities may not become apparent even after the program has been run with hardcopy output, since it would be impracticable to produce too many frames at this stage. The importance of accuracy is illustrated in Fig. 9. For a given position of the lines VU and VS, the co-ordinate values of the points A, B, C and D are calculated [diagram (a)]. The latter are then used to calculated points W and X [diagram (b)], which are then used to calculate the points 7"1 and T2 [diagram (c)]. Thus it is seen that the errors are accumulated from stage to stage and the final construction [diagram (d)] may be distorted if such errors are allowed to creep in. The following points should be noted: (a) the system software produced by A.W.R.E. at Aldermaston causes each frame to be identified by a job number and date, and also to be numbered. This information appears as 'blobs' down the right hand edge of the screen when the film is projected. Modifications to the software are in hand to remove this information. (b) on the Atlas 2 computer at Aldermaston a program will be rejected if it overruns the time allotted to it. The run time required to produce a given number of frames depends on the complexity of the output in terms of the mathematical calculation involved to produce each frame as well as the graphical complexity itself. With the film described in this report, fifteen minutes maximum computer time was requested, and a maximum of 480 frames produced by each run. Also, although not used to produce the film, software facilities are available to repeat frames (up to a maximum of 31 times), without using up extra computer time. By repeating each frame say four times in this way, it would be possible to obtain longer sequences without increasing the costs. This is normally the case with film used in a projector at several frames/second. (c) Again, although not used during the production of the film, software facilities are available for increasing the density of the lines. Thicker lines could also be obtained by repeating the lines slightly displaced, but this method will, of course, increase the computer time required to produce the figure. With reference to the quality of the film images, S. F. Martin of Joseph Kaye and Company Inc., in a letter reproduced in the 1967 year end report of the Computer Animation Committee of U A I D E mentions the following experiences which they have had whilst producing films on an SC 4020, as part of their bureau operations. 1. The SC 4020 camera is not a movie camera. They now use a modified 35 ram. Bell and Howell studio camera. 2. Kodak 5498 RAR film is used because it gives denser lines without image spreading, i.e. higher contrast than other films. 3. High-contrast processing (development in a bath intended for positive prints) is used. 4. The brightness of the tube is measured and the camera adjusted before filming is commenced. From these comments it is apparent that extra care must be taken when using an SC 4020, or similar for movie work (in contrast to normal microfilm work), to obtain good quality film, and that the operators of the equipment must be made 'movie conscious' to ensure consistently good quality results".

The method described here by Dr. Taylor and Mr. Russoff is not dissimilar to the method which is in use at the Polytechnic Institute of Technology in Brooklyn, U.S.A. Here, under the direction of Professor Ludwig Braun, professor of electronic engineering at the Polytechnic, has produced over 30 computer-made films with Dr. Edward Zajac. Dr. Ken Knowlton and Mr. Frank Sinden of Bell Telephone Laboratories. These facilities are now available and constitute an important educational source for many colleges and universities throughout the United States.

Department of Computer Sciences, University of Edinburgh
Dr. J. V. Oldfield and Mr. R. Barfield. This is the other unit we were privileged to work with. Dr. Oldfield describes here briefly the process employed in the production of our other film in the mathematical series, entitled Calculus: "For some time now we have had a computer system fitted with a cathode ray tube display. A programming system called SPINDLE has been developed so that an image may be composed of points, lines and characters. To form a single image involves writing only an elementary program specifying the individual picture parts and where they are to be located. But it would be very tedious to generate an animation sequence by this means, and so several summers ago an undergraduate student, Mr. Barfield, was given the task of writing a program to simplify the process. The program, called AUTO HALAB after its sponsors, allows one to form and control dynamic images. For instance, if we make a triangle of threevertex points and the lines joining them, the program allows us to move a single vertex and automatically force the lines to follow it. With the most basic SPINDLE graphics system each line would have been programmed separately. AUTO HALAB was developed specifically for a series of films on geometry normally made by conventional animation. I t allows images to be composed of points, lines, curves and characters and the various constraints governing them. For instance we may specify that a point must always lie on the line joining two other points. We can then control the developments of the animation sequence by means of invisible 'movers' which cause a specified point to be moved in small steps along a line or curve as successive frames are generated. The computer automatically works out the positions of the other picture parts. Means are provided for changing the size of characters and fading items in and out. As each image is generated, the essential details are recorded in digital form on magnetic tape so that the animator may later control frame-by-frame editing without resorting to the more elaborate initial method. A computer controlled 16 mm. camera produces the final film. More recently a new program has been written so that the animator may describe picture parts and manipulation in three dimensions. To give the illusion of 3-D, the brightness of a line is reduced as it gets further away from the viewer".

Bell Telephone Laboratories Dr. Kenneth Knowlton. An example of how flexible
F O R T R A N can be is shown in the work of Ken Knowlton and Mrs. Lorinda Cherry of the Bell Telephone Laboratories, Murray Hill, New Jersey, U.S.A., who have revised

the BEFLIX movies language, which is a slight revision in F O R T R A N IV to permit easy combination of normal methods and line drawing capabilities of F O R T R A N with the area filling and grey scale facilities of BEFLIX. BEFLIX provides an internal picture storage, as before, consisting of a two-dimensional packed array representing picture elements in a raster-scan representation. The individual installation need only provide four short machine-language subroutines for packing, unpacking and shifting machine words, also the subroutine for outputting a part of this array on its display device, and it must set a few parameters. While the language is quite complex compared with others, it has capabilities for providing a highly rich visual texture, not unlike a tapestry. Dr. Knowlton and Mrs. Cherry describe their system as follows : " F O R T R A N IV BEFLIX is a programming language for the internal creation and/or manipulation of two-dimensional packed arrays - array elements normally standing for picture elements in a raster-scan representation, as in the original BEFLIX animated movie language (Knowlton, S.J.C.C., 1964). The system of subroutines is written almost entirely in FORTRAN IV, requiring only four short machine-language subroutines and a few other minor adjustments for each computer. The outputting of pictures - necessarily machine dependent is left entirely for each installation's implementer to provide for his own configuration of computer and display hardware. Once implemented, the system is used exclusively by means of in-line F O R T R A N coding and F O R T R A N coded subroutine calls (literacy in F O R T R A N is assumed). Thus all of the mathematics of FORTRAN normally used for graphics - e.g. construction of geomet;ic bodies, perspective projection, motion according to differential equations may be easily combined with the grey-scale and area-filling potential of BEFLIX. New uses of BEFLIX itself are also possible, for example one where array elements represent numerical values in a relaxation or other iterative calculation, BEFLIX facilities here providing for the establishment of boundary geometry, two-dimensional bookkeeping during computation, and depiction of results. A Programmer's Description of the Language The BEFLIX programmer imagines a large two-dimensional grid within the machine, each square holding a number. He has at his command scanners called 'bugs' which can crawl about the surface reading and changing the numbers they are siting on, and higher level commands for performing 'drafting' type operations and for manipulating the contents of rectangular subareas. These operations, anJ a few for other miscellaneous purposes, are listed in Table I; a more detailed listing, with parameters, appears in Table II. Operations noted as dynamic are the subroutines'which contain calls to the output routine, thus causing the operation to proceed dynamically in a film."

turn can provide manipulation functions, spacial functions, effects and visual evolution. While the mathematics and logical program necessary to perform this processing may be complex, the language seen by the user must afford control over the technical flexibility available in the program part from the user's non-technical standpoint. The program runs on IBM 360 with a 2250 display unit equipped with a program function keyboard. The IBM, Los Angeles Scientific Center has constructed a control box which acts as an interface between function keyboard and the camera. This device allows the light circuit on the keyboard to activate the camera controls under computer direction to photograph images on the 2250 and advance the film frame-by-frame, and also uses the key circuits as feed back sensors to advise the computer of the camera's status with regard to these controls. One of the leading American experimental film makers, John Witney, has produced a film with this system, entitled Permutations. The main advantage of the digital computer lies in its flexibility and an allowance for diverse approach. The earlier techniques of film making with computers with the aid of a pen type plotter, which can draw a diagram directly on to paper is no longer adequate. Neither is the copying of the photo recorded paper from the SC 4020 plotter. These techniques have been totally replaced by the use of the various high speed c.r.t, recorders, as well as with the multiplicity of subroutine which are available today on both sides of the Atlantic.

Computer Image Corporation
Lee Harrison IlI. The system is described by Mr. Myron P. Smith, Production Director of the Computer Image Corporation, as follows: "The computer approach to the art of film animation was predetermined by the discovery of the art itself at the turn of the century. Every animator has searched for shortcuts, for ways around the drudgery of the cell by cell, frame by frame process. The application of computers in recent years promised an answer - a release from enslaving tedium, and freedom for the artist for his essential function, creativity. The computer brought with it a bewildering array of devices, systems, languages and processes, all of them promising Utopia for animators, and each relying on the mystique of the word 'computer'. But the fulfilment of the promise was slow in coming. One obstacle was consternation among animators who are, first of all, artists, and who, as artists, mistrusted automation of mechanisation. It's a persistent but false assumption that mechanisation or computerisation of the process of animation will destroy or replace the artist. No computer can think or create. But what has occurred is a great deal of misapprehension about what a computer can do, what transformation the artist input must undergo in order to produce computer animation. It is probably safe to say that most systems employing computers or computer technology have frustrated the animator just as they have failed to shorten the time or the work of animation appreciably. Where most computer processes have saved in time in one area or process, they have cost time in another. Animators have accustomed themselves to the inevitability that any system they use involves a delay factor, that there will be a time lapse between the inspiration of creation and the finished animation. This has been a frustrating part of animation from the beginning and makes the animator one of the most patient of all artists. One might speculate

IBM, Los Angeles
Dr. J. P. Citron. Another carefully worked out language for film production is CAMP (Computer Assisted Movie Production), which was developed by Dr. Citron who designed his language in an attempt to avoid dependence upon the user's knowledge of mathematics, geometry and programming logic. He believes that the user should utilise his or her artistic capabilites for which he has provided a clear way of constructing a wide variety of figures which in

Table I Summary of FORTRAN IV BEFLIX grid operations bug operations drafting operations Wl N DOW PLACE MOVE RECT LINE ARC TRACE TYPE PAINT SHIFT TLIT COMBIN CENTER COPY EXPAND SMOOTH FRINGE FILL ZOOM CAMERA DEBUG UPDATE BGREAD LETTER SETRAN RANDOM repositions the window that the internal grid represents places a bug at x, y, coordinates moves a bug draws a rectangle draws a straight line (dynamic) draws an arc or circle (dynamic) traces other curves (dynamic) types alphanumeric characters (dynamic) uniformly paints an area shifts contents of area transliterates numbers combines two areas centres objects (usually typed captions) copies an area enlarges picture by integer factor smooths sharp corners puts a fringe around object(s) fills a bounded area approximates a zoom effect (dynamic) the installation-supplied output routine dubugging aid--prints out a subarea and bug locations repacks words bugs are on unpacks words bugs are on (updates bugs after a subroutine) function for getting nth letter of a string sets output of RANDOM function for delivering random numbers

rectangular area operations

miscellaneous operations

Table II Summary of FORTRAN IV BEFLIX Subroutines and Parameters grid operations WINDOW (xmin, ymin) bug operations PLACE bug, x, y,) MOVE (bug, direction, how far) [xmin ~> 1, ymin >~ 1] [bug: A, B . . . Z] [direction : TO, UP, DOWN, LEFT, RIGHT, NORTH, EAST, SOUTH, WEST]

drafting operations RECT (right, top, left, bottom, n, width) LINE (xl, Yl, x2, Y2, n, width, frames, speed) : ARC (xl, yl, Xc, yc, sense, n, width, x-limit, y-limit, frames, speed) [sense: CW, CCW] TRACE (xl, y~, string, n, width, frames, speed) TYPE (xl, Yl, string, n, size, frames, speed)

t [width :

1,2, 3, 4, 5]

rectangular area operations PAINT (right, top, left, bottom, n) SHIFT (right, top, left, bottom, direction, amount) [direction : UP, DOWN, LEFT, RIGHT] TLIT (right, top, left, bottom, table) COMBIN (right, top, left, bottom, onto-right, onto-top, rule) [rule: BIG, SMALL, SUM, DIFF] CENTER (right, top, left, bottom) COPY (right, top, left, bottom, onto-right, onto-top) EXPAND (right, top, left, bottom, Xc, yc, factor) SMOOTH (right, top, left, bottom) FRINGE (right, top, left, bottom, n, next-to, becomes, flag) FILL (right, top, left, bottom, x, y, n, boundary-n) ZOOM (right, top, left, bottom, xc, yc, factor, frames, speed) miscellaneous operations and functions [installation-supplied output routine] CAMERA DEBUG (right, top, left, bottom, width, height) UPDATE BGREAD LETTER (n, string) RANDOM SETRAN (n, array) SPRING 1971 37

what would have happened to music if Beethoven, Bach or Brahms had had to wait three weeks from the instant they struck a note on the piano before they could hear it. Would we have had the beauty of their music if such were the case ? So it is understandable that the animator has been seeking, from the beginning, any means to reduce delay, and eliminate the exasperation of repetitious procedures. Anyone familiar with animation is aware of the attempts to eliminate the requirement for hundreds or even thousands of interrelated cells necessary to produce the 1,440 frames which comprise a single minute of film animation. Early in the art of animation, the animator created the 'in-betweener" - the assistant who took the animator's grand design and filled in between the keystone drawings. Other tedious tasks were delegated to inkers, colourers, and other supporting skills necessary to produce full colour animation. Another shortcut was a 'cyclical' animation, which devised ways to re-use cells already drawn to produce extended animation. Still, the gap between the creative product and the demand widened. Some animators turned to cutouts, plastic models, pin boards, plotters, pantographs and, most recently, partial animation, in which only the lips and the eyes of the animated character move. Most animators, I think, are aware that few, if any, of these techniques or systems enhanced or advanced the art of animation. They simply created an increasing quantity of product or fill an increasing demand. Then came the computer and the confusion it created. Any system which used a conventional animation stand and was automated in any way, was said to be 'computerised' and therefore capable of producing 'computer animation'. On closer examination, the function of the computer in many systems is secondary. They have, in more recent times, been designated 'off-line" computer animation devices. They move the cell, the table, or the camera of a conventional animation stand in predetermined increments and, thus, save the animation cameraman the boredom of doing these tasks manually. But the computer, if one is used in place of a punch-tape program, does not produce the animation. The grandfather of true computer produced images grew out of the digital computer technology. Perhaps no one knows why the digital system came first, why it has the most disciples, why it attracted the most research, the most money, and the most development. Perhaps it was because digital computers have other applications in business, science and industry. Perhaps there are animators who are not aware of the fundamentals of digital computer technology. In relation to images, digital animation might best be described like this: in order to produce a visible image, a digital computer must construct the image on a cathode ray tube from a series of interconnected dots or points of light digits. In order to create a line, either straight or curved, the digital computer designates the position of a number of interconnected dots. Each time the line moves, the new positions of each of the dots must be recomputed starting with the first, and proceeding sequentially through however many dots are required to create the line. Suppose a reasonably simple image was composed of a number of interconnected lines or surfaces containing 100,000 dots or points of light. The digital computer's memory system is programmed with the position of each of these dots for each frame of film animation. Since programming such a device requires time and since

it constructs the image sequentially, the photography also requires an increased exposure time. The result is not a significant saving of time for the animator, nor can a digital system produce an image of infinite complexity without an infinitely large memory or storage system. Then, too, the animator must learn the computer language appropriate to the computer he's using. This language consists of sequential bits of programmed information which then forms the image, bit by bit and piece by piece. The advantage of digital imagery, however, is precision. But precision, to the degree possible with a digital computer, is more appropriate to science than it is to art. Digital computer animators, however, have made some very significant artistic contributions to animation and if you have seen true computer-animation, most of what you have seen has probably been produced by the digital technique. Most artists, moreover, have somehow been reluctant to adopt it. It doesn't speak their language. Instead it forces them to learn a new one. It is the 'engineer's animation' and, except for some noteworthy exceptions, the engineer-animator-artist is very rare indeed. When Lee Harrison III first conceived the idea for the animation systems now employed by Computer Image Corporation, digital technology was already an established technique. He felt, however, that it had some shortcomings. It was costly and slow, but most detrimental, he thought, it neglected the function of the artist. It worked in a medium which was strange and unfamiliar to animators. His answer to these problems was fundamentally one of simplification. It has come to be called the analogue system, though it does not discriminate against digital techniques, and can and does employ them whenever it is appropriate. The analogue system constructs an image by employing a series of co-ordinated analogue circuits each of which is responsible for repeating only a part of the image. Each analogue circuit operates continuously. That is, instead of producing a part of the image by means of a series of dots, it produces lines by moving an electronic beam over the surface of a cathode ray tube at an extremely high speed or drawing rate. What this means to the artist is that he does not program an analogue or hybrid computer by using computer or engineering language. He modulates or modifies the images he watches by turning a knob. There is no delay factor in an analogue system. The analogue image is modified instantaneously and produced in 'real time', that is, the time it takes to watch it or film it. Because it is made of lines rather than dots, there is a fluidity to analogue animation. The result of the analogue approach has been to produce two hybrid animating systems or devices. The first, called Animac, requires an engineer's knowledge to create the image, whether it be a character or an abstract. But once created, it can be animated without engineering know-how or computer language of any kind. The second system, called Scanimate, can be operated without engineering knowledge by anyone after a half hour's instruction. Its input is any material or art form with which the artist is familiar; a photograph, a drawing, a sculpture. The image of the artist's work is picked up by a special, two-dimensional electronic camera, processed by the computer under the control or instruction of the operator and displayed on a cathode ray tube in animation. Thus far, Scanimate's use has had a limited application to character animation and has been used primarily for what might be called computer graphics. The capability of animating or transforming any graphic material by means of

the Scanimate system; plus the ability of the graphics' designer to stop and photograph the image at any stage of transformation he desires, adds a new creative dimension for graphic artists and designers. F r o m a single design, photograph, or object, complete dimensional control is possible instantly, making this capability applicable to typography and printing, as well as interior and industrial design. A modification of the Scanimate system will be operational in the near future which will produce character animation and will produce it in real time as the animator watches and modifies it. The overall advantage of both Animac and Scanimate, that is, the real time capability, the direct control and immediate variation by the artist, have already been described. But this by no means covers what is perhaps the most important capability. That is, that any kind of artistic input can animate the images. F o r example, the animator's voice, or a voice recording can be used to produce synchronous lip movements in the animated character. The animator can wear a set of attenuators called an anthropometric harness attached to his body and, as he moves, the character moves or animates. This means an animator can choreograph as he watches the resulting animation. Music or sound of any kind can be employed to drive or animate the image or any component of it. There is the capability of direct artistic input and direct artist control. Currently, both Animac and Scanimate images are recorded in monochrome (i.e. black and white) film or videotape. Colour is presently being added by a conventional film printer or by colour keying electronically. The film method adds the laboratory process time to the completion of the finished film. But within a year, full colour, real time animation will be available with any of the Computer Image's animation systems. The long range goal is to produce full colour three-dimensional full animation of the complexity of Fantasia or The Yellow Submarine, in a matter of days or weeks, rather than months or years. If this kind of time schedule for such ambitious production seems to bypass the artist or his creative contributions, please be assured it does not. It is still necessary with the Computer Image systems, as with any computer animated system, for an artist or a group of artists, to provide the creative input. No computer can

circumvent or substitute for this. What it does do, once the creative input has been supplied, is to shorten the time from conception to the realisation of the final product. So far, television has been the chief user of Computer Image animation. Probably because television is more of a voracious consumer of any imagery, no matter what its source. Animators and film producers with varying degrees of experience have used both systems to produce educational and training films, film titles, and film effects as well as television commercials. Computer Image Corporation's next logical and inevitable step is the further development of full character animation. In fact, the capability is already available. It awaits only the creativity of the animator necessary to put it to use." The Future In conclusion both digital and analogue computers can simultaneously contribute image controls far exceeding those of any animation camera or the patience and skill of any animator. And it can perform this task quicker and in many cases cheaper than hand-made animation. It is not impossible that the next Leonardo da Vinci will have a computer terminal in his studio as a part of his artist's equipment. The infinite visual possibilities of computer animation is already exciting more and more artists since it can stimulate both fantasy and imagination. For the time being, however, the artists' contribution is purely experimental. But the challenge to widen the horizon in visual communication is here and is spreading dynamically. At the moment the various systems are most effectively used for education and science. It has been specially successful in space research revealing the movement of satellites in orbit, in physical chemistry dealing with kinetic theory and Newton's Law of motion in electrodynamics in complex engineering and molecular biology. A new aspect of time and space in motion has been presented, complex systems have been revealed clearly for the first time to the wonder and delight of both the professional scientist and his pupil. And now the advertising industry has started to use computer animation. A clear indication that the technique has made it! Received November 1970

J. Halas, F.S.I.A., is a director of Halas and Batchelor Animation Ltd. He is the editor of a book entitled Computer Animation to be published in the summer of this year and has been deeply interested in this subject for some time.



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