| Author: | Chen, Siyuan |
| Title: | Perception of white appearance and degree of chromatic adaptation under different viewing conditions |
| Advisors: | Wei, Minchen (BEEE) |
| Degree: | Ph.D. |
| Year: | 2020 |
| Subject: | Color vision Color -- Psychological aspects LED lighting Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Services Engineering |
| Pages: | xxii, 116 pages : color illustrations |
| Language: | English |
| Abstract: | The colour appearance of a stimulus is affected not only by its spectral composition but also by the viewing condition. When perceiving a stimulus under different viewing conditions, the chromatic adaptation mechanism in the human visual system can automatically remove the colour cast of the illumination, so that the colour appearance of the stimulus remains relatively constant. Colour appearance models (CAMs) embedding chromatic adaptation transforms (CATs) were developed to characterize the colour appearance of stimuli under a limited number of light sources simulating standard illuminants (e.g., Illuminant A, D65, and D50). In recent years, light-emitting diodes (LEDs) are becoming more and more popular for illumination. For luminous efficacy, most white-light LED products contain little amount of radiation in the short and long wavelength regions of the visible spectrum. This was found to affect the white appearance of surface colours. On the other hand, the easy adjustment of the light source chromaticities was also found to affect the degree of the chromatic adaptation, which is critically important to the colour appearance characterizations of a stimulus. This dissertation starts with the investigation of whiteness appearance of surface colours under LED illumination through psychophysical experiments. The whiteness values calculated using the existing whiteness formulae failed to consider the effect of illuminant CCT that degree of chromatic adaptation decreased with the decrease of adapting CCT. An optimization was performed on the degree of chromatic adaptation factor D in CAT02, which significantly improved the performance of the CIE whiteness formula. Furthermore, the whiteness appearance of surface colours was also investigated from a perspective of image appearance. A scene including three whiteness samples containing different amounts of FWAs and a Macbeth ColourChecker was captured by a digital still camera under two 6500 K illuminants with different levels of UV/violet radiation and white balanced using nine statistical algorithms. The lack of UV/violet radiation significantly affected the appearance of the whiteness samples, regardless of the white balance algorithms, which simultaneously affected the appearance of the ColourChecker. The concept of white appearance was further employed to investigate the degrees of chromatic adaptation under different adapting conditions. A psychophysical experiment was conducted to investigate how the adapting CCT and luminance simultaneously affected the degree of chromatic adaptation. It was found that the adapting luminance and CCT jointly affected the degree of chromatic adaptation. Moreover, the experiment results suggested that the viewing mode, instead of the viewing medium, affected the degree of chromatic adaptation. Finally, since Augmented Reality (AR) is becoming more and more popular in recent years, psychophysical experiments were also carried out to investigate chromatic adaptation for viewing optical see-through and video see-through AR setups. Generally, a lower degree of chromatic adaptation was found when viewing virtual stimuli than viewing physical stimuli. In general, this dissertation thoroughly investigated how viewing conditions affected chromatic adaptation through the perception of white appearance of various stimuli. The findings and models are beneficial to various communities related to colour reproduction and imaging through better characterizations of the colour appearance of stimuli. |
| Rights: | All rights reserved |
| Access: | open access |
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