Factors affecting perceived image quality in visual displays : chromatic aberration and accommodation, flicker fusion and visual fatigue

Abstract

The aim of this thesis is to investigate how properties of the early human visual system interact with different types of display technologies and illuminations to determine the quality of the image perceived. The longitudinal chromatic aberration (LCA) of the eye creates a chromatic blur in the retina that serves as an important cue for accommodation. While this mechanism can work optimally in daylight, the effects of modern narrowband illuminants are not completely known. In Chapter 2, we show that LCA causes a dioptric shift in the monochromatic accommodation response curve, while also affecting the slope and resulting visual acuity. In Chapter 3, we show that for two narrowband illuminants, observers accommodate in between the two, decreasing contrast for both, suggesting that these spectra are not optimal to maximise retinal image quality. The relationship between luminous intensity and the maximum frequency of flicker that can be detected defines the limits of our temporal-resolving ability. It is known that critical flicker fusion (CFF) increases as a linear function of log retinal illuminance over four orders of magnitude, but as brighter displays are developed, it becomes important to expand the existing empirical data. In Chapter 4, we show that the CFF increases linearly with luminous intensity over 4 orders of magnitude, where saturation is reached. In Chapter 5, we evaluate the impact that the screen luminance of mobile displays and ambient illuminance have on blink patterns and visual discomfort. While the research on the visual effects of prolonged computer display use is extensive, hand-held devices have not been as widely studied. The results show that lower screen contrast leads to decreased blinking activity and increased visual discomfort. Understanding the impact these factors have on ocular health can be valuable to design hardware and software features that minimise visual fatigue.