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Radiance Maps: An Image-Based Approach to Global Illumination

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Abstract
We present a new image-based approach to global illumination that
is designed to explicitly make use of coherence in the radiance field
of a scene. The approach builds on recently developed ideas from
image-based rendering in order to reuse previously computed geo-
metric and illumination information as far as possible.
The algorithm consists of a hierarchy of three methods, each tak-
ing advantage of a different coherence pattern in the radiance field.
At the top level, we sample primary layered-depth radiance maps of
the environment, thereby abstracting from the exact geometry of the
scene. In the intermediate level, coherence in ray-space is exploited
in order to derive new radiance maps by reprojection from primary
maps. At the lowest level, gradient information is used to spatially
interpolate smooth irradiance contributions, handling non-smooth
contributions separately. Missing or uncertain information in lower
levels is handled by resampling the environment, and feeding these
samples back to adjacent top-level maps. This adaptively improves
the layered-depth images and thus the results of later reprojection
operations.
The essence of our algorithm is an image-based approach to
quickly provide accurate radiance maps anywhere in a scene. In this
paper, we use the radiance maps to compute irradiance in diffuse
environments. However, the comprised information can be used for
a much wider range of applications.