RELATIVE BRIGHTNESS OF SPECULAR AND DIFFUSE REFLECTION

Inhomogeneous dielectric surfaces exhibit both diffuse and specular re flection components. Although various reflection models have been prop osed for both of these components, the prediction of the relative stre ngths of these components in computer vision and computer graphics has so far not had a strong physical motivation. We propose a reflectance model for combined diffuse and specular reflection from dielectric ma terials that involves purely physical parameters (i.e., no ad hoc weig hting of specular and diffuse components). This reflectance model is u sed to predict the relative strength of diffuse and specular reflectio n components in terms of imaging geometry, dielectric surface paramete rs, and solid angular extent of incident light. We derive lower bounds on the contrast ratio between a specularity and surrounding diffuse r eflecting regions. These can be used effectively to rule out highly co ntrasting diffuse reflecting regions being misidentified as specularit ies under a number of conditions that can significantly aid intensity- based specularity detection methods, and in turn image understanding. The presented theoretical developments can be used to predict the phot ometric dynamic range of illuminated objects, which can be essential t o inspection methods in machine vision. These developments can also be used in computer graphics for the physically precise rendering of the relative strengths of specular and diffuse reflection from inhomogene ous dielectrics.