An Introduction to 3D: Recreating the World Inside Your Computer, or Not - Blender Foundations: The Essential Guide to Learning Blender 2.6 - page 7

Simple transparency, based on something called Alpha (Z-transparency in Blender) is quick to render.
Another method of calculating transparency, called ray tracing, takes longer to render but is more
realistic and able to simulate effects like refraction.
● Reflection: Is the surface mirrorlike?
●

Subsurface scattering: Certain real-world materials like skin, jade, or the flesh of a potato exhibit this
property, often abbreviated as SSS. Light enters the material, scatters around, possibly changes color a
bit, then exits. When you hold a flashlight against your fingers in the dark, you see subsurface
scattering.

While these material properties affect an object's overall reaction to light, textures help to define the way
that those properties vary across the surface. Textures can be photo mapped onto a surface, generate bumps
on a surface, or cause transparency to fade in and out, among other things. A careful observation of objects
in the real world will help you to determine which combinations of material settings and textures will
produce the most believable results.

Light
The final ingredient in your still images is light. In the real world, light appears to be easy. You have the
sun and the sky. If you need more light than that, you flip a switch. That's it!

Of course, good photographers know that it's not that simple. Even if they are shooting outside, they
carefully monitor light sources, highlights, and shadows. They might use a reflector to bounce some natural
light into an area that is too deeply in shadow. Indoors, things get even trickier. The great indoor pho-
tography you are used to seeing in magazines (not to mention television and movies) is usually the result
of careful planning and expensive equipment.

It should be no surprise then that lighting in 3D isn't easy. In the real world a lot of lighting, even in
complex commercial situations, is accomplished by the simple fact that light bounces off anything it hits,
and scatters in the air. Shine a focused bright light into a completely dark room and you will be able to
see quite a bit. You will see that objects that aren't even near the beam of light are illuminated, either
from the beam bouncing off the opposite
wall or simple atmospheric scattering. In
3D though, putting a spotlight into a
dark room gets you next to nothing
( Figure 1.8 ).

Some 3D systems allow you to define
lights in a fairly natural way: add a sun,
add a lamp, done. Blender, however,
does not work this way. If you want light
to “bounce” off a far wall, you will have
to add another light source on the wall,
shining in the direction of the bounce.
It can become complicated. Figure 1.8 The project scene with a simple spotlight.