It is known experientially that a feeling of gloss will be affected by sharpness of the reflected light image which is not only the amount of light. In image science, analysis technology is established as sharpness. The typical analysis technology of sharpness is the spatial frequency analysis using MTF (Modulation Transfer Function). However, MTF about specular reflection phenomenon is not well known.
Authors have proposed a concept for Point Spread Function of Specular Reflection (SR-PSF), and have developed this measuring apparatus. Measurement and its analysis of the SR-PSF have been reported (part I). In this study, a concept for Modulation Transfer Function of Specular Reflection (SR-MTF) is proposed, and the spatial frequency analysis of paper gloss by SR-MTF is reported. SR-MTFs of the printing paper are measured. The feature of SR-MTF has low resolution in the incidence direction of light and high resolution in a width direction. In the coated paper for printing, it became clear that SR-MTF has a value only up to spatial frequency about 1.0 (cycles⁄mm).
Image Clarity (JIS-K 7374) and SR-MTF measure the same physical characteristic fundamentally. Because the range of the spatial frequency is too high in Image Clarity, so it is not fit for measurement of the printing paper which has a value only with low spatial frequency. Therefore, the spatial frequency analysis by SR-MTF is fit for paper gloss.
In this study, SR-PSF and SR-MTF of the specular reflection phenomenon were discussed. PSF and MTF are fundamental analysis tools in image science. By having introduced SR-PSF and SR-MTF, a specular reflection phenomenon can be physically analyzed. Moreover, I would like to examine a new reflection model and to apply it to computer graphics.
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