Influence of hue origin on the hue-temperature calibration of thermochromic liquid crystals

Liquid crystal thermography incorporates a process by which the liquid crystal color, bearing temperature information, is analyzed using image processing techniques to quantify complex temperature distributions on heat transfer surfaces. Previous researches have found that hue can be used to represent the liquid crystal color since there exists a monotonic relation between the hue and temperature of liquid crystals. It is found in this study that the white-light point, which is usually adopted as the hue reference point, does not generally lie at the center of the liquid crystal colors defined on a chromaticity diagram. This results that hue does not have uniform resolution to all liquid crystal colors and a biased error is produced subsequently in the temperature measurement. The non-uniform hue can be corrected by shifting the hue origin to the center of the colors or by a color calibration scheme so that the liquid crystal colors distribute evenly around the white-light point.