Computational Imaging for Scene Understanding

9Polarization-Based Shape Estimation

Daisuke MIYAZAKI

Department of Intelligent Systems, Hiroshima City University, Japan

9.1. Fundamental theory of polarization

Light is an electromagnetic wave, and therefore it oscillates. Polarization is a phenomenon in which the direction of light oscillation is biased. Although there is linear polarization and circular polarization, this section only explains linear polarization. Light oscillating in a single direction is called perfectly linear polarized; while light oscillating isotropically is denoted as unpolarized (Figure 9.1). The intermediate state of perfectly polarized and unpolarized can be expressed as partially polarized. DOP (degree of polarization) is a measure that represents the polarization state of light, which ranges from 0 to 1. The DOP of perfectly polarized light is 1 and that of unpolarized light is 0. Light penetrating through the linear polarizer becomes perfectly linear polarized. Light passes through the linear polarizer when its orientation is the same as the orientation of the oscillation of perfectly polarized light. On the contrary, light is blocked when two directions of polarizers are orthogonal.

The brightness of the transmitted light varies depending on the rotation angle of the polarizer if we observe the partially polarized light with a linear polarizer. The polarizer should be set so that the light strikes orthogonally to the polarizer plane. As for the brightness observed when the polarizer is rotated, ...