Fabricate 2.5D Shadow Art Sculpture Yunjoo Park Dept. of Computer Science and Engineering, Ewha Womans University Seoul, Republic of Korea yunjoopark12@gmail.com Jyh-Ming Lien Dept. of Computer Science, George Mason University 4400 University Dr., Fairfax, VA 22124, USA jmlien@cs.gmu.edu Abstract Shadow art is a practice of arranging objects in space to produce surprising shadow. Creating such an art piece has always been labor intensive and time consuming, through trial-and-error methods. Indeed, the time complexity of solving the shadows art problem is inevitably NP hard. In this work, we present a computational method that determines a 2D arrangement of 3D objects to produce a desired shadow image. We demonstrate that the proposed tool successfully reproduce the desired shadow through both simulation and physical fabrication. 1 Introduction The interplay between light and shadow has been a study of art in composing intriguing scenes and images for centuries. In this work, we look into the problem of placing objects in 3D space so they collectively cast a desired shadow. Such an installation consisting of carefully arranged objects and shadows is usually known as shadow art. Figures 1 and 2 show two of such examples. The relationship between the light blocking elements and their composite shadow is usually counterintuitive due the complicated spatial relationships of projection and occlusion and is sometimes even considered as a type of illusion. Because of this creating such an art piece has always been labor intensive and time consuming through trial-and-error methods. In this work, we seek an efficient computational method that automatically determines 3D arrangement of light blockers to cast a desired composite shadow; a problem that, from now on, will be referred to as the shadow art problem. The shadow art problem is closely related to several optimal placement problems, such as geometry packing and covering problems [6, 2, 16, 4]. Therefore, not surprisingly, finding the optimal solution of the shadow art problem has time complexity in NP-hard. Traditional solutions using metaheuristics, e.g. simulated annealing [5], may be used to attack the shadow art problem by packing the given objects in the visual hull of the target shadow, but they often produce unpleasing shadows with jaggy boundaries. Motivated by the ad-hock nature in practice and its computational challenge, we aim to develop a tool that can assist artists creating shadow art more effectively. For example, we will show that our method can help artists create shadow arts with objects arranged on a 2D plane. We believe that the proposed method can produce complicated shadow art that is extremely time consuming to create manually with- out such a computational tool. A video showing the shadow arts created for this paper can be viewed at: https://youtu.be/yVx seXzCvQ