Relationship between PSF and Gonio-reflectance Distribution of Specular Reflection

摘要

Glossiness is one of the important qualities for printing paper. Glossiness is a specular reflection phenomenon in aspect of optics. Therefore, there are various methods of evaluating specular reflection phenomenon. When a person is evaluating the glossiness of paper, it is quite popular to visually inspect the glossiness by the sharpness of the reflected light image. In this paper, it is shown that this visual inspection can be expressed by a transfer function of specular reflection image. First, we discuss the possible use of point spread function of specular reflection (SR-PSF). A technique for measuring SR-PSF of paper is proposed. The measurement principle is a collimator method. This method has been used for the PSF measurement of typical transmittance optical system. We have developed the apparatus to measure SR-PSF. The SR-PSFs were measured for paper samples. The experimental results showed that the measured SR-PSF works as a transfer function for specular reflection image. Second, we show that the apparatus used for measuring SR-PSF also works as a goniophotometer within a narrow solid angle. It is shown that the reflection angle calculated theoretically meets well with that experimentally obtained. That is, a distribution of reflection angle can be calculated using SR-PSF data. It is thought that the spreading of specular reflection observed on paper samples is caused by the distribution of surface normals. Our results showed that SR-PSF and gonio-reflectance distribution are one phenomenon expressed in two different physical concepts. Our future study will be focused on new reflection model for computer graphics.