Tokurei Shogo, Morishita Junji
Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan and Department of Radiology, Yamaguchi University Hospital, 1-1-1 Minamikogushi, Ube, Yamaguchi 755-8505, Japan.
Department of Health Sciences, Faculty of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan.
Med Phys. 2015 Aug;42(8):4773-82. doi: 10.1118/1.4926850.
The aim of this study is to propose a method for the quantitative evaluation of image quality of both monochrome and color liquid-crystal displays (LCDs) using a commercially available color digital camera.
The intensities of the unprocessed red (R), green (G), and blue (B) signals of a camera vary depending on the spectral sensitivity of the image sensor used in the camera. For consistent evaluation of image quality for both monochrome and color LCDs, the unprocessed RGB signals of the camera were converted into gray scale signals that corresponded to the luminance of the LCD. Gray scale signals for the monochrome LCD were evaluated by using only the green channel signals of the camera. For the color LCD, the RGB signals of the camera were converted into gray scale signals by employing weighting factors (WFs) for each RGB channel. A line image displayed on the color LCD was simulated on the monochrome LCD by using a software application for subpixel driving in order to verify the WF-based conversion method. Furthermore, the results obtained by different types of commercially available color cameras and a photometric camera were compared to examine the consistency of the authors' method. Finally, image quality for both the monochrome and color LCDs was assessed by measuring modulation transfer functions (MTFs) and Wiener spectra (WS).
The authors' results demonstrated that the proposed method for calibrating the spectral sensitivity of the camera resulted in a consistent and reliable evaluation of the luminance of monochrome and color LCDs. The MTFs and WS showed different characteristics for the two LCD types owing to difference in the subpixel structure. The MTF in the vertical direction of the color LCD was superior to that of the monochrome LCD, although the WS in the vertical direction of the color LCD was inferior to that of the monochrome LCD as a result of luminance fluctuations in RGB subpixels.
The authors' method based on the use of a commercially available color camera is useful to evaluate and understand the display performances of both monochrome and color LCDs in radiology departments.
本研究旨在提出一种使用市售彩色数码相机对单色和彩色液晶显示器（LCD）图像质量进行定量评估的方法。
相机未处理的红（R）、绿（G）和蓝（B）信号强度取决于相机中使用的图像传感器的光谱灵敏度。为了对单色和彩色LCD的图像质量进行一致评估，将相机未处理的RGB信号转换为与LCD亮度相对应的灰度信号。单色LCD的灰度信号仅通过使用相机的绿色通道信号进行评估。对于彩色LCD，通过为每个RGB通道采用加权因子（WF）将相机的RGB信号转换为灰度信号。为了验证基于WF的转换方法，使用用于子像素驱动的软件应用程序在单色LCD上模拟彩色LCD上显示的线图像。此外，比较了不同类型市售彩色相机和光度相机获得的结果，以检验作者方法的一致性。最后，通过测量调制传递函数（MTF）和维纳频谱（WS）评估单色和彩色LCD的图像质量。
作者的结果表明，所提出的校准相机光谱灵敏度的方法对单色和彩色LCD的亮度进行了一致且可靠的评估。由于子像素结构的差异，MTF和WS在两种LCD类型中表现出不同的特性。彩色LCD垂直方向的MTF优于单色LCD，尽管由于RGB子像素中的亮度波动，彩色LCD垂直方向的WS不如单色LCD。
作者基于使用市售彩色相机的方法有助于评估和理解放射科中单色和彩色LCD的显示性能。
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