The present paper describes a method for estimating the refraction index of the material of an object surface with arbitrary convex shape in natural scenes. The refraction index cannot be neglected for describing the specular reflection function, while the absorption index can be neglected for the dielectric material. In fact, note that the intensity of specular highlight depends greatly upon the index refraction of the surface material. In this paper, we consider estimating the refraction index for any object surfaces of inhomogeneous dielectric materials in natural scenes by using a general CCD camera. This parameter is estimated from the sensor measurements for specular highlight intensity of an object surface at different conditions of illumination and viewing. The estimated refraction index is compared with direct measurements using a refractmeter. The accomplishment of this estimation leads us to complete estimation of various parameters of the Torrance-Sparrow model.