Shadow modelling based upon Rayleigh scattering and Mie theory

• We propose a method to model the shadow in outdoor imagery.
• Shadow areas is assumed to correspond to the scattered light obeying Rayleigh scattering and Mie theory.
• Shadow area recovery is cast into a clustering setting making use of active contour.
• A formulation of a metric is proposed to assess the degree upon which the scene is overcast.
• We compare the shadow detection and the time complexity results against the alternative methods in real world imagery.

In this paper, we present a method to model shadows in outdoor scenes. Here, we note that the shadow areas correspond to the diffuse skylight which arises from the scattering of the sunlight by particles in the atmosphere. This yields a treatment in which shadows in the image can be viewed as a linear combination of scattered light obeying Rayleigh scattering and Mie theory. This allows for the computation of a ratio which permits casting the problem of recovering the shadowed areas in the image into a clustering setting making use of active contours. This also opens-up the formulation of a metric that can be used to assess the degree upon which the scene is overcast. We illustrate the utility of the method for purposes of detecting shadows in real-world imagery, provide time complexity results and compare against a number of alternatives elsewhere in the literature.