The effects of illumination direction on the perception of 3D shape from shading

3rd Place at the Denman Undergraduate Research Forum 2016A fundamental problem for the perception of 3D shape from shading is to achieve some level of constancy over variations in the pattern of illumination. The present research was designed to investigate how changes in the direction of illumination influence the apparent shapes of surfaces. The stimuli included images of 3D surfaces with Lambertian reflectance functions that were illuminated by a rectangular area light source. The direction of illumination was systematically manipulated. Observers judged the 3D shapes of these surfaces by marking local depth minima and maxima along three designated scan lines using a hand-held mouse. The results revealed that the local depth maxima were shifted slightly toward the direction of illumination, while the local depth minima were shifted slightly away from the direction of illumination. However, these changes were much smaller than what would be expected based on differences in the pattern of luminance among the stimulus images. These findings demonstrate that there is a substantial amount of illumination constancy in the perception of 3D shape from shading, but that it is not perfect. Several hypotheses are considered about how this constancy could potentially be achieved.No embargoAcademic Major: Psycholog

Distortion in 3D shape estimation with changes in illumination

In many domains it is very important that observers form an accurate percept of 3-dimensional structure from 2-dimensional images of scenes or objects. This is particularly relevant for designers who need to make decisions concerning the refinement of novel objects that haven't been physically built yet. This study presents the results of two experiments whose goal was to test the effect of lighting direction on the shape perception of smooth surfaces using shading and lighting techniques commonly used in modeling and design software. The first experiment consisted of a 2 alternate forced choice task which compared the effect of the amount of shape difference between smooth surfaces lit by a single point light with whether the position of the light sources were the same or different for each surface. Results show that, as the difference between the shapes decreased, participants were more and more biased towards choosing the match shape lit by the same source as the test shape. In the second experiment, participants had to report the orientation at equivalent probe locations on pairs of smooth surfaces presented simultaneously, using gauge figures. The surfaces could either be the same or slightly different and the light source of each shape could either be at the same relative location or offset by 90° horizontally. Participants reported large differences in surface orientation when the lighting condition was different, even when the shapes were the same, confirming the first results. Our findings show that lighting conditions can have a strong effect on 3-dimensional perception, and suggest that great care should be taken when projection systems are used for 3D visualisation where an accurate representation is required, either by carefully choosing lighting conditions or by using more realistic rendering techniques