Dichromatic separation: specularity removal and editing

The reflectance of a wide variety of materials (plastics, plant leaves, glazed ceramics, human skin, fruits and vegetables, paper, leather, etc.) can be described as a linear combination of specular and diffuse components, and for many applications we can benefit from separating an image in this way. Figures 2 and 3, for example, depict photo-editing and e-cosmetic applications in which visual effects are simulated by independently processing separated diffuse and specular image layers. Similarly, specular/diffuse separation plays an important role for image-based modeling applications in which diffuse (specular-free) texture maps are sought. Separation of the two reflectance components in a single image is an ill-posed problem. In the past its solution has required the manual identification of highlight regions, the use of special acquisition systems (e.g., polarizing filters), or restrictive assumptions about the scene (e.g., untextured surfaces). Recently, we have introduced a method for specular/diffuse separation that overcomes many of these limitations [Mallick et al. 2006], and in this sketch, we build on this work, showing how it can be used for dichromatic editing — processing and recombining the two reflectance components for various visual effects. We present results on high-quality images and videos acquired in the laboratory in addition to images taken from the Internet. Results on the latter demonstrate robustness to low dynamic range, JPEG artifacts, and lack of knowledge of illuminant color. Similar to most existing techniques for specular/diffuse separation, our approach is based on exploiting color differences between specular and diffuse reflections as described by Shafer’s dichromatic model. According to this model, the color of the specular component at each surface point is the same as that of the illuminant (S), while the color of the diffuse component depends on the reflectance of the surface and can change from point to point.