Generation of omni-directional HDR light probe images based on the intensity distribution model around the sun

Abstract

When synthesizing CG images with real image as a background, it is necessary to estimate the lighting environment such as intensities and directions of light sources from real images. In previous study [Baba et al. 2016], except for the high intensity area such as the sun, light source information was estimated by concerning pixels of the captured image as light sources having corresponding intensities[Debevec 1998]. For a high intensity area, the intensity of the light source was estimated from the ratio of the intensity of the shadow area and the sunshine area[Sato et al. 2003]. However, since the sun is used as one parallel light source, there is a problem that it can express only a sharp shadow and it can not be reproduced as an HDR light probe images. Figure 2(a) shows a real image. Figure 2(b) shows a rendering result by the conventional method. In the Figure 2(b), the penumbra of the upper part of the shadow can not be expressed and the shadow boundary is clear comparing with the real image.