Is the perception of 3D shape from shading based on assumed reflectance and illumination?

James T Todd,Eric J L Egan,Flip Phillips

doi:10.1068/i0645

Abstract

The research described in the present article was designed to compare three types of image shading: one generated with a Lambertian BRDF and homogeneous illumination such that image intensity was determined entirely by local surface orientation irrespective of position; one that was textured with a linear intensity gradient, such that image intensity was determined entirely by local surface position irrespective of orientation; and another that was generated with a Lambertian BRDF and inhomogeneous illumination such that image intensity was influenced by both position and orientation. A gauge figure adjustment task was used to measure observers' perceptions of local surface orientation on the depicted surfaces, and the probe points included 60 pairs of regions that both had the same orientation. The results show clearly that observers' perceptions of these three types of stimuli were remarkably similar, and that probe regions with similar apparent orientations could have large differences in image intensity. This latter finding is incompatible with any process for computing shape from shading that assumes any plausible reflectance function combined with any possible homogeneous illumination.

Highlights

One of the most difficult problems in the study of human perception involves the ability of observers to correctly interpret patterns of image shading
The light that reflects from a visible surface toward the point of observation is influenced by three factors: (1) the surface geometry, (2) the pattern of illumination, and (3) the manner in which the surface material interacts with light
The image in Panel A was again rendered with a Lambertian bi-directional reflectance distribution function (BRDF) using a collimated light field that was parallel to the viewing direction; the one in Panel B was textured with a linear intensity gradient that was oriented at a 45° angle to each of the primary axes; and Panels D and E show the patterns of isophotes for these images

Summary

Introduction

One of the most difficult problems in the study of human perception involves the ability of observers to correctly interpret patterns of image shading. The traditional approach to computing shape from shading is based on an assumption that all variations in luminance are due entirely to variations in surface orientation It is typically assumed, for example, that a surface has a Lambertian reflectance function that scatters light in all directions, and that it is illuminated homogeneously by a collimated light field. This is not possible based on any process that computes 3D shape using an assumed BRDF with an assumed homogeneous illumination.

Experiment 1

Findings

Discussion