Point Spread Function of Specular Reflection and Gonio-Reflectance Distribution
Shinichi Inoue
Process Development Laboratories, Mitsubishi Paper Mills Limited, 3 Maeyamanishi, Nishigomura, Nishishirakawa-gun,
Fukushima 961-8054, Japan
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Norimichi Tsumura
Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan
Abstract
In this article, the specular reflection phenomenon is analyzed by the
concept of the point spread function (PSF). The conventional PSF, which
is a sharpness criterion, is used for the transfer function in image science.
In general, print (an ink image on paper) is observed as diffuse reflection
light, and the light source image, i.e., gloss, is observed as specular
reflection. We first introduce the point spread function of specular reflection
(SR-PSF). A measurement principle for the SR-PSF is proposed, and a measurement
apparatus for the SR-PSF is developed by using a collimator optical system.
The experimental results show that the measured SR-PSF works as a transfer
function for a specular reflection image. Each detected position is in
agreement with the angle of reflected light. The apparatus works as a goniophotometer
within a narrow solid angle. The relation between the SR-PSF and the specular
reflection angle distribution is discussed in terms of surface geometry.
It is concluded that the measured data are the SR-PSF and they have a gonio-reflectance
distribution. The reflection angle is caused by the surface normal, and
the surface normal distribution can be calculated from the gonio-reflectance
distribution by using the mathematical model. We plan to apply our proposed
principle to the development of an evaluation technique for the visual
gloss. In addition, the high-resolution goniophotometer can be further
developed by this measuring technique.
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