COMPUTER ANIMATION AND VIRTUAL WORLDS Comp. Anim. Virtual Worlds 2016; 27:113–121 Published online 9 February 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cav.1633 RESEARCH ARTICLE Interactive digital graffiti canvas system Yong Sun Kim*, Yongwan Kim and Ki-Hong Kim Virtual Reality Research Lab., Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon, 305-700, Republic of Korea ABSTRACT This paper presents an interactive digital painting system that allows a user to draw graffiti on a virtual 3D canvas with a digital spray can. The system visualizes a stereoscopic representation of the canvas by tracking the user’s head. It also emulates real-time spray painting by tracking the spray can in the user’s hand as well as sensing the button pressure of the spray device. After painting a 3D object, the user can interact with the object on the display and see it flying in the 3D environment through a tracked head-mounted display. As demonstrated in the results of our evaluation, we verified that the system resembles real graffiti in regard to a natural and realistic graffiti experience. Copyright © 2015 John Wiley & Sons, Ltd. KEYWORDS digital graffiti; digital spray can; spray simulation; virtual reality *Correspondence Yong Sun Kim, Virtual Reality Research Lab., Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon 305-700, Republic of Korea. E-mail: yongsun.kim@etri.re.kr 1. INTRODUCTION Graffiti is the art of painting or drawing on a wall in a public place, usually accomplished today with spray cans. While recently graffiti art has been in the spotlight for creating beautiful urban landscapes, graffiti artworks in public places without permission are generally illegal, and so graffiti must be permitted beforehand. Graffiti is a kind of disposable art, in that it often disappears quickly. There- fore, graffiti art is hard to recreate and share with others. Some graffiti may also cause problems with the graffiti artist’s health and air pollution because aerosol spray paint is the most commonly used tool. Recently, virtual reality (VR) technologies have been increasingly applied to present virtual experiences that are hard to achieve in real life. Using state-of-the-art VR technology, we propose a digital graffiti canvas sys- tem that addresses the problems of real graffiti art. In a virtual environment, the digital graffiti art becomes environment-friendly, and it is not necessary to obtain per- mission in advance. Users can perform graffiti repeatedly without any additional consumables. Instead of using an actual aerosol spray, we have designed a digital spray can that is free from toxic chemicals. On our system, graffiti artworks become recreatable and can be shared online. Our digital graffiti system provides a sensation similar to painting real graffiti on a wall, by incorporating paint simulation with a pressure-controllable digital spray can, stereo visualization, and a tracking device. Our system sup- ports functionalities such as saving, e-mailing, and printing to cherish or share the paintings. Furthermore, our system supports virtual interaction with the digitally painted object and extends the viewing zone of 3D TV using an opti- cal see-through head-mounted display (HMD) for seamless visualization of the digital graffiti art. 2. RELATED WORK We briefly review related researches on virtual spray paint- ing and case studies on virtual graffiti systems. A couple of VR-based graffiti systems have been proposed in the liter- ature [1,2]. The virtual graffiti system in [1] was equipped with a projection-based cave automatic virtual environ- ment. A pair of pinch gloves was used to operate spraying, control the menu, or navigate around the 3D environ- ment. A dummy spray can was tracked by a magnetic tracker. This projection-based system is inevitably bulky, and users may experience inconvenience due to wearing gloves. Unlike real graffiti, their spray device cannot con- trol button pressure. The digital airbrush system in [2] was equipped with an infrared light-emitting spray can. Copyright © 2015 John Wiley & Sons, Ltd. 113