Reflections on Radiosity
Problem: Rendering
scenes with standard lights in Lightwave produces a nonrealistic result.
Reason: When rendering Lightwave calculates lights on a source to
collision basis. This means that rays are calculated as emanating from the
source (the light) until they collide with their target (what ever object is in
the line of the ray). The reason this produces unrealistic results is that real
world light isn't entirely absorbed when it hits an object. Only a small
portion is absorbed the rest is reflected elsewhere. So when you have a light
in your scene shining off of a red wall, the objects near the wall should have
a hint of red reflecting off of them. And so on and so on and so on. Obviously
it is not efficient to calculate multiple light bounces in all scenes.
Top: 9 second render using point light.
Middle: 1 minute 6 second render using area light.
Bottom: 23 minute 24 second render using luminous polygon with radiosity.
Solution: Radiosity.
Radiosity is an option in lightwave found by clicking global
illumination in the light properties dialogue box. Checking the 'Enable
Radiosity' box will turn radiosity on. Radiosity works best in scenes that are
indoors because of the high occurrence of light bouncing back and forth between
objects and walls. It can also make low resolution objects look much better
than they would in the default-rendering environment.
There are three options when using radiosity: Monte Carlo, Interpolated, and
Back Drop Only.
Monte Carlo produces the most accurate "real world" result by
calculating all rays. This greatly increases rendering time. The rays per
evaluation setting increases the number of possible directions light can bounce
off of a given polygon, increasing this number increases the accuracy of the
final product but also increases the rendering time.
Interpolated calculates a majority of rays and estimates the in-between
values and blends them together. Interpolated allows for error, but can
significantly decrease rendering time. It is possible to set the level of error
tolerance with the interpolated setting by adjusting the tolerance value.
Increasing the tolerance value increases the number of rays that are estimated
and decreased the number that are actually calculated. Tolerance can be set
from 0 to 1; the default for interpolated is .3. You can also adjust the
minimum evaluation spacing. This tells the rendering engine to average values
that are within a certain distance from each other, which can speed up
rendering. One problem with the interpolated setting is that the final image
can vary from frame to frame which makes animating with interpolated look
choppy and jittery.
Backdrop Only takes only the rays that emanate from the backdrop into
consideration. This option works well with outdoor scenes because it allows you
to light a scene using the backdrop as you light source. However, backdrop only
doesn't account for light bouncing between objects nor does it allow for
luminous objects.
Rendered using area
light, no radiosity.
Rendered using interpolated radiosity with luminous dome.
Luminous objects
Radiosity allows you to light your scene using objects instead of lights. This
can produce very realistic results and save time in positioning lights. If you
are creating a scene with a lamp in it you can assign luminosity to the surface
of the lamp's light bulb in the surface editor. Then render the scene with
radiosity on and the light bulb will illuminate the scene. This technique can
also be used to create light sources that have complex geometry like bent fluorescent
lights or neon signs.
