Issue No.10 - October (2011 vol.17)
Marcio Cabral , REVES/INRIA, Sophia Antipolis
Nicolas Bonneel , REVES/INRIA, Sophia Antipolis and University of British Columbia, Vancouver
Sylvain Lefebvre , REVES/INRIA, Sophia Antipolis
George Drettakis , REVES/INRIA, Sophia Antipolis
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/TVCG.2010.236
We present an image-based approach to relighting photographs of tree canopies. Our goal is to minimize capture overhead; thus the only input required is a set of photographs of the tree taken at a single time of day, while allowing relighting at any other time. We first analyze lighting in a tree canopy both theoretically and using simulations. From this analysis, we observe that tree canopy lighting is similar to volumetric illumination. We assume a single-scattering volumetric lighting model for tree canopies, and diffuse leaf reflectance; we validate our assumptions with synthetic renderings. We create a volumetric representation of the tree from 10-12 images taken at a single time of day and use a single-scattering participating media lighting model. An analytical sun and sky illumination model provides consistent representation of lighting for the captured input and unknown target times. We relight the input image by applying a ratio of the target and input time lighting representations. We compute this representation efficiently by simultaneously coding transmittance from the sky and to the eye in spherical harmonics. We validate our method by relighting images of synthetic trees and comparing to path-traced solutions. We also present results for photographs, validating with time-lapse ground truth sequences.
Image-based rendering, relighting.
Marcio Cabral, Nicolas Bonneel, Sylvain Lefebvre, George Drettakis, "Relighting Photographs of Tree Canopies", IEEE Transactions on Visualization & Computer Graphics, vol.17, no. 10, pp. 1459-1474, October 2011, doi:10.1109/TVCG.2010.236