LED Illumination and Color Appearance of White-Balanced Images

ABSTRACT

Recent studies revealed the failure of typical blue-pumped white light emitting diodes (LEDs) in rendering the white appearance of surface colors, which was caused by the lack of ultraviolet (UV)/violet radiation to excite the fluorescent whitening agents (FWAs). The effect of such a failure on image color appearance has not been previously investigated, though white surfaces are important in image white balance. In this study, two 6500 K sources—one containing a normal level of UV/violet radiation to simulate CIE standard D65 and the other containing a low level of UV/violet radiation to simulate typical blue-pumped white LEDs—were created to illuminate a Macbeth ColorChecker and three whiteness standards containing different amounts of FWAs. The scene was captured and white balanced using nine different algorithms. Though the two sources caused small color differences to the ColorChecker, both physically (ΔE*_ab = 1.44) and in the unbalanced images (ΔE*_ab = 2.53), the source with a low level of UV/violet radiation caused noticeable color shifts to the ColorChecker in the white-balanced images regardless of the algorithms. Furthermore, the chromaticities of the three whiteness standards were all shifted toward the origin in the a*–b* plane under the source with a low level of UV/violet radiation in the white-balanced images regardless of the algorithms, making them appear more similar to each other. Overall, the findings suggested the great impact of typical blue-pumped white LEDs on image color appearance.

KEYWORDS:

• Color difference
• fluorescent whitening agents (FWAs)
• image color appearance
• LED illumination
• white balance

Disclosure statement

The authors report no declarations of interest.

Additional information

Funding

This study was funded by the Research Grant Council of the Hong Kong Special Administrative Region, China (PolyU 252029/16E).