Graphics Reference
In-Depth Information
Chapter 5
Visual Perception
The human eye dominates the field of computer graphics, for without it, graph-
ics would be almost useless. Everyone working in graphics should understand
something about how the visual system works. Until some day when graphics is
“perfect” and somehow indistinguishable from reality, we must try to best use our
computational and display resources to convince the visual system that it's per-
ceiving reality, which entails omitting work that produces undetectable (or barely
detectable) differences from the ideal.
This chapter introduces some important basic ideas, as well as outlining the
limitations of our current understanding. The science of human vision and the
related science of machine vision are lively areas of research precisely because
of the richness of these limitations. Of course, a great deal
is
known, and we'll
summarize some of it here.
The visual system's remarkable parallel processing powers allow enormous
amounts of information to be transferred from the computer to the user. (The lim-
itations on bandwidth in the other direction—human to computer—are a source
of frustration and opportunity for clever design; see Chapter 21.) The visual sys-
tem is both tolerant of bad data (which is why the visual system can make sense
of a child's stick-figure drawing, or an image rendered with a very crude lighting
model), and at the same time remarkably sensitive. Indeed, the eye is so sensitive
to certain kinds of error that debugging graphics programs entails special chal-
lenges: A single tiny error (one red pixel in a 1-million-pixel grayscale image of
a lighted sphere) stands out, while a one-in-a-million error in many other compu-
tations might never be noticed. There's a converse to this as well, which we men-
tioned earlier: We can use imagery to convey an enormous amount about what a
program is doing, so good graphics programmers use visual displays to help them
understand and debug their code.
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