Realism And Features Supporting Lightness Constancy In Virtual Scenes

Lighting and surface properties play an important role in visual perception. Our visual system decodes two-dimensional retinal images to discern potential three-dimensional scenes. A particular challenge in the context of achromatic lights and surfaces is lightness constancy — the ability to maintain a consistent perception of an object’s reflectance despite varying illumination conditions. Although humans are generally adept at maintaining lightness constancy, it is not perfect. This dissertation examines lightness constancy within both real-world and virtual environments, including flat-panel displays and virtual reality (VR). Chapter 2 evaluates lightness constancy through an asymmetric lightness matching task across a shadow boundary, using physical surfaces, a flat-panel display, and an immersive VR environment. While the VR condition exhibited realistic levels of lightness constancy, participants showed significantly lower levels of constancy in flat-panel display compared to the physical environment. Notably, participant variability was more pronounced in both virtual environments. In Chapter 3 the study extends to lightness matching across various 3D orientations using both physical surfaces and in VR. The findings reveal that lightness constancy is significantly weaker in VR compared to physical environments. Building on Chapter 3, Chapter 4 further evaluates lightness constancy using the same task, but incorporates more realistic and accurate rendering techniques, along with realistic materials, in VR. Contrary to expectations, the results show no notable improvement in lightness constancy, underscoring the persistent challenges in achieving realism for tasks evaluating lightness across 3D orientations in VR. Despite robust 3D shape, lighting, and depth cues available in VR, constancy is significantly worse in VR and our understanding of lightness perception fails to explain why. This discrepancy highlights a gap in our knowledge, pointing to potentially overlooked factors critical for accurate lightness perception, such as fine material details or subtle surface textures. In conclusion, the findings in this dissertation suggest that VR is a reasonable proxy for real-world scenarios in tasks when lightness is judged across a shadow boundary, but current technology falls short in replicating realistic lightness constancy when image luminance varies from one location to another due to differences in 3D orientation relative to a light source.