Rendering a CG Scene - An Introduction to Computer Graphics for Artists - page 224

light. One of these devices is called a refl ector . A refl ector is a screen that comes in
a variety of colors that can be attached to a tripod. It is designed to produce smooth,
even bounce light . For this reason, its surface is unwrinkled, but has a fi ne texture
that disrupts the direction of refl ected light, to remove the hard edge it would other-
wise project. These are placed around objects in a scene to intensify, direct, or
change the color of bounce light (Fig. 12.7 ). They work because all things refl ect
and receive light to some degree. A refl ector is not the origin of a photon, but serves
to modify and redirect ambient photons in a scene.

12.5.4.6 Ambient

Ambient light is what allows you to see things inside your house during the day,
even though no lights are turned on. Sunlight washes over everything because,
after direct rays arrive inside through windows, they continue bouncing throughout
your house, lighting up even deep corners. Shadows cast by ambient light can
be dim and soft or hard and strong, depending on the intensity of the source. The
presence of true ambient light in a scene is very diffi cult to accurately calculate
for a cg rendering, and it is for this reason many cheats have been invented to
get around it.

12.5.4.7 Spot

Spot lights will cast a hard light and shadow in a given direction based on the orien-
tation of the light and the shape of its housing. Spotlights are an excellent means of
directing attention towards an element in your scene. With the right modifi cations,
spotlights can cast a variety of different types of light at a very small part of a scene
they are aimed at.

12.5.5 CG Light Types

In any given CG scene there are many light sources of various intensities and types.
Not all of them are lights, but in one way or another, light comes off them to illumi-
nate something else. The way it works is that photons from an initial light source, a
light emitter , are projected outwards. These photons travel until they strike some-
thing and are either absorbed completely, partly absorbed, or refl ected. The refl ected
light is usually a different color than it was initially, and of lesser intensity, having
lost some of its original strength during the process of partial absorption and refl ec-
tion. This process repeats itself as the photon continues to refl ect and be absorbed,
until there is nothing left to absorb or refl ect. Practically speaking, most renderers
simply have a cutoff value below which no further calculations are made.