Reflectance and Shape Estimation for Cartoon Shaded Objects

Although many photorealistic relighting methods provide a way to change the illumination of objects in a digital photograph, it is currently difficult to relight a cartoon shading style in digital illustrations. The main difference between photorealistic and cartoon shading styles is that cartoon shading is characterized by soft color quantization and nonlinear color variations that cause noticeable reconstruction errors under a physical reflectance assumption such as Lambertian. To handle this non-photorealistic shading property, we focus on the shading analysis of the most fundamental cartoon shading technique. Based on its color map shading representation, we propose a simple method to decompose the input shading to a smooth shape with a nonlinear reflectance property. We have conducted simple ground-truth evaluations to compare our results to those obtained by other approaches.