Simplified Light Probe using Minimal Number of Photodiodes

Many display system users have strongly desired that a superimposed virtual object of computer graphics (CG) have optical consistency with a real object at a scene. For this study, we model a real-world light environment as one point light source at infinite distance and an environmental light, which has only three parameters: the point light direction and intensity ratios of the two light sources. We propose a simplified light probe sensor that has five photo IC diodes on each surface of a square pillar, except at its bottom, to estimate the three parameters. The five outputs of the photo IC diode under specific model parameters are obtainable analytically because the directivity characteristics of photo IC diode are approximated as a cosine of the incident angle. The three parameters are then derived from the five outputs. The parameter estimation entails very low computational cost. Experimental results demonstrate sufficient estimation accuracy to render a CG object without a feeling of strangeness.