Akamine Hiroshi, Morishita Junji, Matsuyama Michinobu, Nakamura Yasuhiko, Hashimoto Noriyuki, Toyofuku Fukai
Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Med Phys. 2012 Aug;39(8):5127-35. doi: 10.1118/1.4737869.
The color characteristics of medical liquid-crystal displays (LCDs) have become one of the main interests in quality assurance and quality control of medical display devices. It is necessary to evaluate variations of the color characteristics in medical LCDs in order to provide consistent color characteristics for image reading. In this study, we characterize the color characteristics in grayscale images displayed on medical LCDs.
Eight medical color LCDs and eight medical monochrome LCDs were used in this study with operating times ranging from 800 to 25 000 h. Default settings of correlated color temperature (CCT) of white points for all color LCDs were set at 7500 K. We measured chromaticity in the Commission Internationale de l'Éclairage (CIE) u'v' color space and CCT of the white point at 18 luminance levels. A colorimeter and grayscale test patterns with various luminance levels were used for the measurements. First, we examined differences in chromaticity and CCT at 18 luminance levels for each LCD. Second, we compared chromaticities of the different LCDs. Then, chromaticity and CCT of LCDs were measured at different ambient light conditions (30 and 560 lux) and compared to those measured in a dark room. Finally, the relationship between operating times and CCT was evaluated.
The chromaticities of monochrome LCDs changed toward the blue and CCT increased as luminance decreased. In color LCDs, the chromaticity and CCT of the white point except at the minimum luminance were nearly constant to those measured at the maximum luminance. We observed differences in chromaticity between color and monochrome LCDs because of the nonadjustable white point of monochrome LCDs. When the ambient light increased, chromaticity varied, and CCT decreased on every LCD. Ambient light had a much greater impact on chromaticity and CCT at lower luminance levels. The CCT of LCDs decreased in longer operating times. The grayscale of LCDs with longer operating times was measured to be more yellowish due to the degradation of cold cathode fluorescent lamps.
Our results clearly indicate that the white point in grayscale images displayed on medical LCDs changes depending on luminance levels, color or monochrome LCDs, ambient light conditions, and operating times. These data provide useful information to understand color characteristics of LCD for image reading, especially for quality assurance and quality control of LCDs.
医用液晶显示器（LCD）的颜色特性已成为医用显示设备质量保证和质量控制的主要关注点之一。为了在图像读取时提供一致的颜色特性，有必要评估医用LCD颜色特性的变化。在本研究中，我们对医用LCD上显示的灰度图像的颜色特性进行了表征。
本研究使用了8台医用彩色LCD和8台医用单色LCD，工作时间从800小时到25000小时不等。所有彩色LCD的白点相关色温（CCT）默认设置为7500K。我们在国际照明委员会（CIE）u'v'颜色空间中测量了18个亮度水平下的色度以及白点的CCT。使用色度计和具有不同亮度水平的灰度测试图案进行测量。首先，我们检查了每个LCD在18个亮度水平下的色度和CCT差异。其次，我们比较了不同LCD的色度。然后，在不同的环境光条件（30和560勒克斯）下测量LCD的色度和CCT，并与在暗室中测量的结果进行比较。最后，评估工作时间与CCT之间的关系。
单色LCD的色度随着亮度降低而向蓝色变化，CCT增加。在彩色LCD中，除最低亮度外，白点的色度和CCT与在最高亮度下测量的结果几乎恒定。由于单色LCD的白点不可调节，我们观察到彩色和单色LCD之间的色度存在差异。当环境光增加时，每个LCD的色度都会变化，CCT会降低。在较低亮度水平下，环境光对色度和CCT的影响更大。LCD的CCT在较长的工作时间内会降低。由于冷阴极荧光灯的老化，工作时间较长的LCD的灰度被测量为更偏黄。
我们的结果清楚地表明，医用LCD上显示的灰度图像中的白点会根据亮度水平、彩色或单色LCD、环境光条件和工作时间而变化。这些数据为理解用于图像读取的LCD的颜色特性提供了有用的信息，特别是对于LCD的质量保证和质量控制。
