Communications of the ACM
Inexpensive real-time image generation and control
ACM SIGGRAPH Computer Graphics
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With the proliferation of extremely complex analog systems for the control of television images it has become evident that some more efficient system has to be found for dealing with the mire of knobs, switches, levers, and patch cords which make up any video processing device. In planning an attack on this situation, we soon realized that a major aspect of the problem is a linquistic one. Television has only a few terms which deal with the almost infinite number of effects possible in any given system. The specification of wipes, fades, dissolves, keys, etc. tells one the process used, but does not go into great detail as to what it looks like on the screen. A circle wipe, for instance, may start in any part of the screen, have an edge in any of several degrees of softness, may be modulated by a wide range of frequencies, and may have a number of outlines around it in any combination of colors. Given these technical capabilities, the problem of how to catalog the possible effects and how to specify them was approached in terms of a description based on a Cartesian coordinate system representation of the multidimensional video space. The use of such a coordinate system has given us several advantages. The first is that there is a large body of existing work dealing with physical movements along orthogonal axes. Secondly, image color in television can be measured or specified in terms of phase shifts from 0 to 360 degrees in a planar reference axis system. Another consideration which makes this description natural is that it is standard for zero voltage on a CRT display to be center screen, thus defining our origin and relating it in a simple way to the physical control values. With this as our point of departure we embarked on our work with the clear realization that, because the dimensions and variability of the system were almost infinite, due to the unconstrained combination of analog patches and digital programming, some severe restraint would be necessary in order to make the results meaningful.