Rendering a CG Scene - An Introduction to Computer Graphics for Artists - page 219

type of renderer used. Frames from a feature fi lm can be rendered in as little as a few
minutes, or as much as dozens of hours. Even at 2 min a frame, which may not seem
like much, such scenes could not be used in a real-time video game. For that, the
scene would have to render thousands of times faster. The difference between ren-
der times for offl ine and inline renderers is the primary reason that art made for
video games looks so much different from CG art in feature fi lms.

12.5 Lights

Lighting will determine whether your render is appealing or not. No matter how
well built every other element of your scene is, if your lighting is poor, the quality
of the objects in your scene will not be evident. Poor lighting is the easiest way to
destroy the good effect of work well done, just as it is the best way to resuscitate
even mediocre efforts.
The basics of lighting are easily stated, but understanding only comes from prac-
ticed observation of how light behaves, both in the real world and within the con-
fi nes of a cg scene. Real world lighting is concerned primarily with factors relevant
to aesthetic appeal, and virtual lighting is often only meant to imitate real world
lighting. Because it is important that any real world lighting used as an example is
of good quality, this chapter begins with photographic lighting; its goals, methods,
and some standards by which its success is judged.
A light source such as the sun, a match, or an incandescent bulb emits pho-
tons . These particles travel away from the source as rays . Light from the sun is
so distant from their point of origin that its rays are considered parallel. Nearer
sources, like a light bulb, discernibly push photons outward at every angle. When
an object blocks a photons' path, it is either absorbed or refl ected as bounce light
(Fig. 12.4 ). Either way, because photons have been blocked, they do not travel
through an object to light the other side. Shadows are not, as they seem to be, a
dark color that is cast from an object, but are more like a hole in the lighting cast
on surrounding objects.

12.5.1 Aesthetic Appeal

For a photographer, the most basic goals are these: Structural clarity, mood and
beauty. Achieving these three things has nothing to do with being realistic, but using
light to paint the scene in such a way that anyone looking at it will understand any
photos made from it. Regardless of the style of the photographer, any professionally
made photo will be legible, clear, and stylish. These goals are important to the cg
artist also, because without them, his work will not demand the kind of attention
that a well done work of art always gets.
To “paint” a scene with light, still life photographers will literally light the differ-
ent parts of their scene one-by-one, adding and subtracting light elements as