Natural Material Segmentation and Classification Using Polarisation
This paper uses polarisation information for surface segmentation based on material reflectance characteristics. Both polarised and unpolarised light is used, and the method is hence applicable to both specular or diffuse polarisation. We use moments to estimate the mean-intensity, polarisation and phase from images obtained with multiple polariser orientations. From the Fresnel theory, the azimuth angle of the surface normal is determined by the phase angle and for a limited range of refractive index the zenith angle is determined by the degree of polarisation. Using these properties, we show how the angular distribution of the mean intensity for remitted light can be parameterised using spherical harmonics. We explore two applications of our technique, namely a) detecting skin lesions in damaged fruit, and b) exploiting spherical harmonic co-efficients to segment surfaces into regions of different material composition using normalized graph cuts.