Graphics Reference
In-Depth Information
The problem of accurately capturing images covering a wide range of bright-
nesses, and the problem of recovering the lighting information from environment
images were originally treated as separate problems. While working on
The Cam-
panile Movie
, Debevec had a vague idea of treating the background image as a
source of lighting. After developing a method to create HDR images, he turned to
the problem of recovering lighting information from real-life background images.
Debevec thought of performing global illumination calculations by treating
the pixels in the HDR background image as light sources scattered around the
background of the CG environment. Trying this out required a good set of GI
rendering tools. Luckily, Greg Ward, whom Debevec came to know through his
work on HDR images, had already added functionality to the RADIANCE system
that could performGI using environmentmaps. Debevec proceeded to develop his
rendering system using this idea and created the first test images in RADIANCE.
Although Ward had doubts about whether Debevec's idea could be realized, they
were both pleasantly surprised by the results.
The method used to create these test images was presented at SIGGRAPH in
the paper “Rendering Synthetic Objects into Real Scenes” [Debevec 98]. How-
ever, the term “image-based lighting” was never actually used in the paper. The
termwas first coined when Debevec's series of animated films were shown in Ger-
many using the title “Image-Based Modeling, Rendering and Lighting.” Debevec
took a great liking to the phrase “image-based lighting” and used it in subsequent
publications and presentations. Before long, the term “IBL” became well estab-
lished in the CG field.
7.1.2 The Basic Process of IBL
Figure 7.1 illustrates the basic process described in Debevec's “Rendering Syn-
thetic Objects into Real Scenes” paper. The “real scene” in this figure is a table
with some real objects. The goal is to add a CG object (on the tabletop) to a pho-
tograph of this scene so that it looks like a part of the original scene. The steps
are outlined as follows.
1. The scene is photographed; the CG object will be composited into this im-
age
(
Figure 7.1(a)
).
2. The lighting of the environment is obtained at the point where the CG ob-
ject is to be placed. This is done by photographing a
light probe
,which
is a mirrored sphere placed in the environment where the CG object will
go. The light probe is photographed from several viewpoints, each using a
range of exposure times (
Figure 7.1(b)
)
.
