NDLI: Frequency analysis and sheared filtering for shadow light fields of complex occluders

Content Provider	ACM Digital Library
Author	Egan, Kevin Ramamoorthi, Ravi Hecht, Florian Durand, Frédo
Copyright Year	2011
Abstract	Monte Carlo ray tracing of soft shadows produced by area lighting and intricate geometries, such as the shadows through plant leaves or arrays of blockers, is a critical challenge. The final image often has relatively smooth shadow patterns, since it integrates over the light source. However, Monte Carlo rendering exhibits considerable noise even at high sample counts because of the large variance of the integrand due to the intricate shadow function. This article develops an efficient diffuse soft shadow technique for mid to far occluders that relies on a new 4D cache and sheared reconstruction filter. For this, we first derive a frequency analysis of shadows for planar area lights and complex occluders. Our analysis subsumes convolution soft shadows for parallel planes as a special case. It allows us to derive 4D sheared filters that enable lower sampling rates for soft shadows. While previous sheared-reconstruction techniques were able primarily to index samples according to screen position, we need to perform reconstruction at surface receiver points that integrate over vastly different shapes in the reconstruction domain. This is why we develop a new light-field-like 4D data structure to store shadowing values and depth information. Any ray tracing system that shoots shadow rays can easily incorporate our method to greatly reduce sampling rates for diffuse soft shadows.
Starting Page	1
Ending Page	13
Page Count	13
File Format	PDF
ISSN	07300301
e-ISSN	15577368
DOI	10.1145/1944846.1944849
Volume Number	30
Issue Number	2
Journal	ACM Transactions on Graphics (TOG)
Language	English
Publisher	Association for Computing Machinery (ACM)
Publisher Date	2011-04-22
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Soft shadows Area lights Frequency analysis Light fields Sampling Sheared reconstruction
Content Type	Text
Resource Type	Article
Subject	Computer Graphics and Computer-Aided Design

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4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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