Graphics Programs Reference
In-Depth Information
HDRI
As you saw in the Final Gather section, FG
rendering is based on the illumination in the
scene from lights as well as the brightness of
objects in the scene, such as a light dome. In
the previous section, you used an incandescent
dome to light the still-life scene. But what if
you were to use an image instead of just white
for the light dome?
Furthermore, what if the image you used
was an High Dynamic Range Image (HDRI)?
In Chapter 1, we briefly discussed HDR images.
Several photos at varying exposures are taken
of the same subject, ranging from very dark
(low exposure) to highlight only the brightest parts of the scene, all the way up to very
bright (overexposure) to capture the absolute darkest parts of
the scene. When these images (usually five or seven images)
are compiled into an HDR image, you get a fantastic range of
bright to dark for that one subject.
How does this help you light? With image-based light-
ing (IBL), mental ray creates an environment sphere in your
scene to which you assign an image, usually an HDRI. That
environment sphere, much like the white dome in the Final
Gather exercise earlier in the chapter, uses the brightness of its
image to cast light in your Maya scene.
The best type of image to capture for an IBL is sometimes
called a
light probe
. This is a picture of an environment, such
as the office reflected in a chrome ball shown in Figure 11.82.
You can also take a light probe using a fish-eye camera lens
capable of capturing a field of view of close to 180 degrees.
Figure 11.82 shows the middle exposure of five exposures
taken of the same office. Figure 11.83 shows the range from
underexposed (dark) to overexposed (bright) of the five pho-
tos that were used to compile the HDRI of the desk you'll be
using to light the decorative box in the next section.
The photos are compiled in an HDR image file (called
DeskHDR.hdr
in the
Sourceimages
folder of the Decorative_Box
project on the CD) for the next section's IBL lighting exercise
and as shown in Figure 11.84. You won't be able to see the
Figure 11.82
A light-probe photo
of a desk is taken
with a chrome ball.
Figure 11.83
The five exposures
that make up the
HDRI of the desk to
be used in the next
section.
