Chapter 13
HDRI and
Caustics
This chapter covers HDRI, or High Dynamic Range Images, and caus-
tics. In addition, you will learn some methods of employing these tools
in your scenes.
Note: In the past, these techniques were seldom used in pro-
duction. With the advent of ever-more-powerful processing and
the availability of relatively inexpensive large render farms, these
techniques, especially the use of HDRI for lighting, have become
commonplace in the production pipeline. There seems to be a con-
sensus (generally among those who are not experienced lighting
artists) that HDRI is the only way to achieve great lighting. This is
absolutely false. HDRI can provide a shortcut to lighting a scene,
but has the added effect of locking you down to specific lighting
and removing art and design from the process. Because HDRI is
most often used to automate the lighting process, many lighting
opportunities may be lost, as control is given over to the computer.
If you are looking to build an assembly-line lighting department,
then HDRI is just the thing for you. HDRI lighting cannot create
quality superior to other, less expensive techniques used by a
skilled lighting artist.
The universe contains a wide range of visible illumination. The human
eye can detect extremely low levels of light but has an upper threshold.
Light above this threshold can cause pain and even retinal damage.
Enter the iris. The iris opens very wide under low-light conditions to
allow as much light as possible into the eye. In brighter conditions such
as a plainly lit office, your iris will close somewhat, allowing less light in
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