Scene Segmentation Using Polarisation Information

This thesis draws its hypothesis from the quantitative description of reflection and refraction of light at interfaces, given by the Fresnel theory. According to the theory, initially unpolarised light is partially polarised upon reflection from a smooth dielectric surface. Hence, variations in the polarisation properties of reflected and scattered light must indicate a change in properties of the reflecting surface. Assuming internal changes in refractive index can be neglected, any substantial change in the polarisation of light is thus indicative of a change in the material remitting the light. The contribution of this thesis is to develop a method for image segmentation based on surface material characteristics. The novel aspects of the method are the expression of intensity distribution as a function of the surface zenith and azimuth angles, and the expansion of this function using spherical harmonics to estimate surface characteristics. The method begins with estimating shape from polarisation using [1]. The surface normals obtained are used in combination with pixel intensities to form a three dimensional function that describes intensity changes in the image. This function is then expanded as a harmonic series and the constants of the expansion are used as features to characterize image regions and to segment the image based on the hypothesis. Experimental evidence is presented through analysis of polarisation images and segmentation of images of different objects.