Page 24 - Studio-International-January-1974

No doubt the introduction of this sort of generated from mathematical equations or read
technique for drawing curves into 'computer in from cards, they have tended to become the
art' owes much to the mathematics-oriented stock-in-trade of 'computer art'. Indeed, it
programmer, who would tend to view a curve would be difficult to see how any computer
essentially as the graph of a mathematical animation involving drawn images could
function. But not all curves can be handled in proceed without such transformations.
this somewhat simplistic way, and artists wishing For our purposes, however, the question to be
to handle more complex curves have been asked is whether the notion of a picture
obliged mostly to use an entirely different processor, operating upon some previously
approach, if anything even more simplistic. generated image, corresponds in any useful way Figure 10
Since it is possible to describe any point by its to what we know of human art-making
HOZ-VERT pair, it follows that any drawing behaviour. I think the answer has to be that it factors controlling the current phase are
can be approximated by a set of points, each does not. To achieve that correspondance, the immediately reset and a new full phase is
of which can be treated in the same way, so that machine would need to generate the image, not initiated, starting off in the opposite direction.
the whole drawing can be described in purely merely to process it. It should be noted also that the line has some
numerical terms. Imagine then that you have Intuitively, it seems obvious that the human definite destination and corrects continuously
already done a drawing, that you have reduced process involves characteristics which are quite in order to get to it. The programme would
it to a string of points, and that you have typed absent from these procedures, and in particular look something like this :
the HOZ and VERT values of each point I think we associate with it an elaborate feed-
together with its PEN code, on a series of back system between the work and the artist;
punched cards (or, of course, any other and dependent upon this system are equally
storage medium for which the computer elaborate decision-making procedures for
has the appropriate peripheral). A programme determining subsequent 'moves' in the work.
like this Our enquiry might reasonably proceed by
examining whether the machine is capable of
simulating these characteristics.
Before going on, I must explain that the
computer possesses one significant ability which
was implied by the earlier examples but never
explicitly stated. It is able to compare two
things, and on the basis of whether some
particular relationship holds between them or
not, to proceed to one of two different parts of
would then simply read the first card to find the programme. In practice this primitive
the first point in the drawing (PEN decision-making device can be built into
would presumably be o until it gets here), logical structures of great complexity, with the
move the pen to that point, read the next alternative paths involving large blocks of
card for the next point, and so on until it programme, each containing many such
has done all the points. The machine has conditional statements, or 'branches'.
duplicated your drawing from your numerical It would be quite difficult to demonstrate a
description. complex example here in any detail. The
drawing on the cover of this issue of
Studio International was generated by a
programme of about 500 statements, of which
over 5o were concatenated from these simple
conditionals, equivalent to about 85 branches.
We might look at one part of that programme,
however, about 5o statements in all, which
generates the individual 'freehand' lines in the
drawing. Obviously the flow-chart is a much-
simplified representation.
The argument behind the sub-programme this structure does evidently possess a feed
runs like this : in any 'sub-phase' of a line's back system not unlike the kind we employ in
Figure 9 growth it will be swinging to the left or to the driving a car. There is an overall plan — to reach
right of its main direction (`straight on' if given a destination — which breaks down into a
It may not be clear why anyone would want to by swing= o). This swing may be constant, succession of sub-plans, which are in turn
use such elaborate means to reproduce a drawing accelerating or decelerating, and both the rate of responsible for generating a series of single
he has already made. The answer is that quite a swing and the rate of change of swing may be movements. But if an 'emergency' is signalled,
lot of things can be done to the drawing by either slow or rapid. Overall, the line must not the current sub-plan is abandoned, and a new
suitable programmes. Not only can it be reduced, swing beyond a certain pre-set angle from its one set up.
enlarged, shifted, rotated, squashed up, pulled main direction. A single full phase will consist of The quality of the line is directly related to
out (Fig. 9): it can also be transformed as if two sub-phases normally swinging in opposite the way in which the factors for each new sub-
it were drawn on a sheet of rubber which was directions. Both of these, and the phase itself, phase are reset: if the length of each sub-phase
then stretched in various irregular ways. None may vary in length, and normally the starting varies enormously, or if the rate of change of
of these operations, or transformations as they direction for each full phase does not depend on swing varies greatly from one to the next, the
are called, is difficult to programme, and since that of the previous one. If the line swings line will tend to be quite erratic. If the angular
they can be applied to any set of points whether beyond its angular limit, however, all the limits are set quite small — by the over-all plan —

14