Tatsuya Deguchi

Clarification of “Gamma” and the Accurate Characterization of CRT Monitors

Color images are often viewed on CRT monitors with the widespread PCs and Internet. We clarified the term “gamma1)” which represents the monitors tone characteristics, since this term is ambiguously used. Also, an accurate characterization method of CRT monitors was considered because it is essential to have color matching with other color imaging devices. We compared several characterization methods at different settings of the user-controlled contrast and brightness, and found a more accurate characterization method than the conventional methods.

Effect of user controls on CRT monitor characteristics

CRT monitors are widely used for desktop publishing (DTP) and to view images on the Internet. The color images on the computer graphic display can be printed out or displayed on other monitors through the Internet. Here, color matching between the original image on the monitor and the printed image or the image displayed on other monitors is very important. The current color management systems (CMSs) are useful for the color matching. These CMSs utilize device profiles, such as ICC profiles, in which color characteristic information is stored. These profiles are generated by device characterization. Thus, an accurate characterization of the monitor is essential for better color matching. According to the ICC specification, monitor characteristics can be described by the chromaticity and the tone reproduction curves (TRCs) of the red, green and blue channels. Although the monitor profiles on the current CMSs are based on the assumption that the monitors are maintained at the default adjustment and are viewed in a dark room, in fact the user often adjusts the settings of contrast/brightness and usually views the monitor under ambient light. In this paper, we investigated the effect of user controls on CRT monitor characteristics. We reconsidered the two characteristics of the CRT monitor: the effect of user controls on the TRCs and interaction among the channels. We compared several models of the TRC and various matrices to transform linearized RGB to CIE 1931 XYZ with different settings of the user controls. Based on these experimental results, we propose a method for more accurate monitor characterization.