Modeling effect of shading: New approach

Abstract

One purpose of lighting is to help in the perception of an object's three-dimensional form. The quality of lighting that does this is sometimes called 'the modelling effect of light' and it helps people see a solid form by creating a gradient of light across the surface of the object. This paper reports on a study which investigated the manner in which the pattern of light alone creates a sense of solidity in an object and relates this to the processing of visual information in terms of spatial frequencies. It is suggested that the human visual system identifies bands of spatial frequencies in the pattern of light incident on the retina and that the information is transmitted by two different visual pathways. Further, it is hypothesised that the perceived depth of a simple solid form can be predicted by considering the relationship between the information carried by the two visual pathways. Using a computer to process an image of a simply lit regular solid form, the investigators were able to analyse the frequency components in an image and then weight them according to two given frequency responses, in order to provide a measure of the stimulation in the two visual pathways. In this experiment a corrugated wave object was used. It was lit horizontally to avoid any specially apprehensive psychological effect. The data were then used to assess the importance of different spatial frequencies in the perception of apparent depth in the image of the solid form. Apparent depths of the image were estimated by comparing with a real object.