Visual Comput (2008) 24: 753–763 DOI 10.1007/s00371-008-0257-5 ORIGINAL ARTICLE Naoto Okaichi Henry Johan Takashi Imagire Tomoyuki Nishita A virtual painting knife Published online: 5 June 2008  Springer-Verlag 2008 Electronic supplementary material The online version of this article (doi:10.1007/s00371-008-0257-5) contains supplementary material, which is available to authorized users. N. Okaichi (✉) · T. Imagire · T. Nishita The University of Tokyo 277-8561 Japan {okaichi, imagire, nis}@nis-lab.is.s.u-tokyo.ac.jp H. Johan Nanyang Technological University Nanyang Avenue, Singapore 639798 henryjohan@ntu.edu.sg T. Imagire Namco Bandai Games Inc. Santa Clara, CA 95054, USA Abstract Recently, in the area of non-photorealistic rendering, there has been a significant effort in digital painting research to sim- ulate traditional painting styles and painting pigments. In particular, the simulation of painting tools is very important because this enables an intuitive painting experience for a user and generates rich painting effects. Many painting systems have been proposed using brushes, but less for other painting tools. As a result, there is still a limitation in the variety of painting effects that can be generated. In this paper, we propose a method to simulate paint- ing using a painting knife, which is an important tool in oil painting. We model a painting knife and model the pigments such that the system is suitable for realizing the impasto style. We also present a technique for simulating the interaction between a painting knife and pigments on a canvas in real-time. Keywords Non-photorealistic ren- dering · Painting systems · Painting knife model 1 Introduction In non-photorealistic rendering, many methods have been proposed for simulating traditional painting styles, such as watercolor, oil painting, ink painting. Generally, the simulations of these painting styles are realized by sim- ulating the painting tools and pigments. However, al- though in the simulation of painting tools, the modeling of brushes and painting with brushes have been extensively researched, other painting tools have been hardly consid- ered at all. Nowadays, digital painting software, such as Photo- shop [1] and Painter [8], are frequently used by artists. These packages have the following advantages: – The user can undo and redo any changes. – Once the user buys the software, he/she needs to buy neither physical pigments nor materials. – The images made by digital painting software do not deteriorate with age. However, since existing software do not simulate the painting tools and pigments in 3D space, they can only generate 2D effects. In other words, they cannot generate 3D effects, such as the many different kinds of footprints (traces of painting) and realistic bumps that are commonly found in real paintings.