Graphics Reference
In-Depth Information
7
Image-Based Lighting
7.1 The Basics of Image-Based Lighting
In the production of special effects for live action films, objects created with CG
are composited with real life video frames that contain the background and some-
times live actors. In order to perform this compositing without noticeable visual
inconsistencies, there is a need to recreate, as accurately as possible, the lighting
of the real scene and to render the CG objects using this lighting. One method is to
capture images of a white polystyrene or metallic sphere positioned in the scene
where the CG object would be and perform CG lighting based on the captured
images. However, this requires a lot of trial and error and provides a limited mea-
surement of the scene lighting. More accurate—and more automatic—methods
were needed. It can be said that the awareness of this issue led to the concep-
tion and practical application of
image-based lighting
(IBL), in which lighting is
reconstructed directly from photographs of the original environment.
7.1.1 The Birth of IBL
As mentioned earlier, Paul Debevec became interested in high dynamic range
imaging during his work on the
The Campanile Movie
[Debevec 97]; however,
HDR was not the only issue that troubled him during the creation of that film.
Debevec's goal of photorealistically rendering computer-generated objects within
real environments required the CG objects to be illuminated by the lighting cap-
tured from the environments. The lighting information used in image-based ren-
dering was combined with the object textures. What was needed was a way to
separate the lighting information from the general appearance of objects using
the captured images.
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