“Combining spherical harmonics and point-source illumination for efficient image-based relighting” by Tunwattanapong, Ghosh and Debevec

Traditional image-based relighting technique requires capturing a dense set of lighting directions surrounding the object and uses the linearity of light transport property together with the illumination data of the target environment to relight an object [Debevec et al. 2000]. However, this can be a very data intensive process because such datasets typically involve photographing hundreds of lighting directions. It is also difficult to modify or edit the data in post-production environments because the data is high dimensional. Adjustment has to be made in several dimensions in order to add artistic effects to the result. Difficulty in acquisition process is also one of the main problems. The capturing process typically lasts long enough to only be suitable for static objects. In this poster, we present a relighting technique which greatly reduces the number of images required for relighting, and still generate realistic results. We combine spherical harmonics with point lights to achieve efficient image based relighting. Spherical harmonics can efficiently capture smooth low frequency illumination [Ramamoorthi and Hanrahan 2001] while point lights capture high frequency directional illumination. Combining both techniques, we create relighting results which have both low and high frequency illumination data. This technique also benefits the acquisition process by reducing the number of required photographs which results in shorter capture time. In addition, fewer dimensions of the data can potentially simplify modification or editing of reflectance data.

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2. Ramamoorthi, R., and Hanrahan, P. 2001. An efficient representation for irradiance environment maps. In SIGGRAPH ’01: Proceedings of the 28th annual conference on Computer graphics and interactive techniques, ACM, New York, NY, USA, 497–500.