Imaging simulation for non-Lambertian objects observed through a light-scattering medium

摘要

Imaging characteristics are covered by the image transfer theory. But up to now, image transfer theory dealt mainly with observation of Lambertian (diffuse reflecting) objects on a Lambertian background. This model of reflection is quite a reasonable one for many natural and artificial objects to describe vision quality. We present here the mathematical description for images of non-lambertian objects to permit their angular reflection patterns to be dealt with under unfavorable viewing conditions through a light-scattering medium. Retroreflectors are chosen as an convenient example of these objects. The small-angle diffusion approximation of the radiative transfer theory is used for the calculations of light characteristics under illumination by some source of an active vision system. The case studies consider, in particular: (1) Imaging of large-area objects where some of their parts would be seen as dark and others as bright, and (2) the interesting effect of enhancing the contrast of a retroreflector image with increasing optical thickness of a scattering medium. This is related to increasing the ''effective'' albedo of an ''equivalent'' Lambertian object, by which the retroreflector can be replaced. The results on imaging characteristics of retroreflective objects are compared with those for Lambertian. The corresponding differences are discussed.