Abstract Shape Extraction For Watercolor Tree Rendering Using Anisotropic Density Functions

Abstract

Trees are important in synthesizing outdoor scenes. One of the features of trees is their complicated shape composed of many leaves, branches and trunks. In many non-photorealistic rendering methods, abstract shapes are required to convey the information of shape to the viewer. Luft and Deussen proposed a method that extracts abstract shapes from tree polygon models, which adopted isotropic density functions for leaves. The leaves are generally flat, however, so that their method tends to extract the abstract shape with dilation. This paper proposes an abstract shape extraction method that utilizes anisotropic density functions to capture anisotropic structures of leaves. The proposed method was implemented and the several types of tree models were tested. This paper also introduces metrics to evaluate dilation and erosion of extracted shapes. The result shows that the dilation and erosion can be controlled by choosing the parameters, so that users can extract abstract shapes in several styles according to their preference.