Takeshi HARAGUCHI^1,2, Taka-aki SUZUKI³, and Katsunori OKAJIMA⁴

¹TOSHIBA TEC CORPORATION, Izunokuni, Shizuoka 410-2392, Japan
²Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama 240-8501, Japan
³Industrial Research Institute of Shizuoka Prefecture, Shizuoka 421-1298, Japan
⁴Faculty of Environment and Information Sciences, Yokohama National University, Yokohama 240-8501, Japan

(Received April 29, 2009; Accepted August 18, 2009)

In the present study, we measured the visibility of several types of Japanese text on a liquid crystal display (LCD) with a spatially inhomogeneous luminance and extended the visibility index function (VIF) to explain the current experimental results with a higher degree of accuracy. We quantitatively analyzed the effect of an inhomogeneous luminance, which was produced by the graphical representation of a background without reflected light and by reflected light on a homogeneous background. These results showed that the visibility of text was influenced by the inhomogeneity of the background luminance in a domain that depended on text size. Then we applied a weighted average background luminance with a two dimensional Gaussian function, whose distribution width was related to the text size, to VIF. Finally, we proposed a modified VIF and showed that the new method was able to precisely estimate the actual visibility of text with an inhomogeneous luminance.

Key words: visibility, quantification, visibility index function (VIF), subjective evaluation, inhomogeneity