Graphics Reference
In-Depth Information
Chapter 34
In the early days of computer graphics, researchers sought to make any picture
that resembled our eyes' view of a real object; photographs were considered
completely realistic, and hence the goal of photorealism emerged. With further
thought, one realizes that each photograph is just one possible condensation of
the light field arriving at the camera lens; different lens and shutter and exposure
settings, film or sensor types, etc., all change the captured image. Nonetheless, the
term “photorealism” survives. When researchers began to think about other forms
of imagery, they used the term “nonphotorealistic rendering” or NPR to describe
it. Stanislaw Ulam said that talking about nonlinear science is like talking about
nonelephant animals; we correspondingly prefer the term
expressive rendering,
which captures the notion of
intent
in creating such a rendering: The picture is
meant to communicate something more than the raw facts of the incoming light.
Most traditional “rendering” (as in “an artist's rendering of a scene”) has not
aimed for strict photorealism. Given the wealth of experience gathered by artists
and illustrators about effective ways to portray things, we can learn much by exam-
ining their work. In doing so, we must consider the artists'
intent:
while some
have aimed for photorealism, others have tried to convey an impression that some
scene made upon them, while still others have aimed for condensed communica-
tion (think of illustrators of auto-repair manuals) or highly abstract representations
(see Figure 34.1). The intent of the work influences the choices made: The stylistic
choices made by Toulouse-Lautrec, conveying the mood of a Parisian nightclub,
are very different from those made by Leonardo depicting the musculature of the
human arm.
We characterize expressive rendering as work that is concerned with
style,
intent, message,
and
abstraction,
none of which can be easily defined precisely.
Scene
modeling
can also create a style or support an artistic intent (think of set
design in theatre or scene design in films), and careful composition can con-
vey intent or exhibit abstraction even in photographs. So there's no clear line
of demarcation between “expressive rendering” and “photorealism.” Nonetheless,
there are things that seem to fall naturally into one or the other category, and this
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