Calculating surface reflectance using a single-bounce model of mutual reflection

Light reflected from one surface onto a second surface changes both the intensity and spectral power distribution of light leaving the second surface. Similarly, light from the second surface illuminates the first. This mutual reflection effect can be exploited by examining pixels where interreflection is and is not present. From these measurements several intrinsic properties can be determined: the reflectance of each surface, the spectral power distribution of the incident illumination, and some constraints on the physical configuration of the two surfaces. The authors use finite dimensional linear models for the ambient illumination and for surface spectral reflectance, with m basis functions for illumination and n for surfaces. Examining p sensor values (e.g. RGB values) they find that if p satisfies the condition p⩾(2 n+m)/3 they can solve for finite dimensional model descriptors of both surfaces and of the ambient illumination, as well as for a form-factor stemming from the surface configuration. With n =m=3, p can also be 3. A single-bounce model of mutual reflection accounts for the most important contribution to light intensity in an interreflecting geometry