It is known that the performance of liquid-crystal display (LCD) monitors, such as the luminance and contrast ratio, is dependent on the viewing angle. Our purpose in this study was to compare the angular performance and the effect on observer performance of different types of LCD monitors. The luminance performance and contrast ratio as a function of viewing angle (-60° to 60°) in each direction for two types of LCD monitors, namely, a general-purpose LCD monitor and one especially designed for medical use, were measured in this study. Furthermore, the observer performance at various viewing angles in the horizontal direction for a medical-grade LCD monitor was investigated by eight observers based on a contrast-detail diagram. The two types of LCD monitors showed notable variations in luminance and contrast ratio as a function of the viewing angle. Acceptable viewing angles in terms of the contrast ratio were much smaller in each direction than those for nominal viewing angles in the specifications provided by the manufacturers, and those for the medical-grade LCD monitor in the horizontal and vertical directions were broader than those of the general-purpose LCD monitor. There was no significant difference in observer performance between 0°and 40°. On the other hand, our results showed a statistically significant difference in observer performance between 0°and 60°.
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