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

Published: 22 April 2011 Publication History

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.

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  1. Frequency analysis and sheared filtering for shadow light fields of complex occluders

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    Published In

    cover image ACM Transactions on Graphics
    ACM Transactions on Graphics  Volume 30, Issue 2
    April 2011
    104 pages
    ISSN:0730-0301
    EISSN:1557-7368
    DOI:10.1145/1944846
    Issue’s Table of Contents
    Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

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    Publication History

    Published: 22 April 2011
    Accepted: 01 December 2010
    Revised: 01 November 2010
    Received: 01 October 2010
    Published in TOG Volume 30, Issue 2

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    Author Tags

    1. Soft shadows
    2. area lights
    3. frequency analysis
    4. light fields
    5. sampling
    6. sheared reconstruction

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