Impact of fluorescent whitening agent excitation on White Balance Algorithms

Various white balance algorithms, based either on the Gray World assumption or on the Retinex theory, have been developed to remove the color cast of illumination in images. Though most man-made white objects contain different amount of fluorescent whitening agents (FWAs) to enhance and create different degrees of whiteness appearance, the FWA excitation has seldom been considered in white balance algorithms. In this study, four illuminants, comprising 2 levels of CCT and 2 levels of UV/violet radiations, were produced to illuminate a setup, which included a Macbeth ColorChecker and a calibrated whiteness standard. Three whiteness standards containing different amount of FWAs were used under each illuminant, with one present each time. It was found the FWA excitation generally caused little color difference to the algorithms based on the Gray World assumption, which was likely due to the small size of the whiteness standard in the image. In contrast, the performance of the algorithms based on the Retinex theory was largely affected by the FWA excitation, as the FWA excitation affected the RGB values of the pixels for adjusting the gain factors. Given the wide usage of blue-pumped white LEDs that contained little UV/violet radiation for enhancing luminous efficacy in general illumination, the impact of the FWAs is not trivial and should be considered in developing white balance algorithms.