Intelligent Camera Control Using Behavior Trees Daniel Markowitz, Joseph T. Kider Jr., Alexander Shoulson, and Norman I. Badler Department of Computer and Information Science University of Pennsylvania Philadelphia, PA 19104-6389, USA {idaniel,kiderj,shoulson,badler}@seas.upenn.edu Abstract. Automatic camera systems produce very basic animations for virtual worlds. Users often view environments through two types of cameras: a camera that they control manually, or a very basic automatic camera that follows their character, minimizing occlusions. Real cine- matography features much more variety producing more robust stories. Cameras shoot establishing shots, close-ups, tracking shots, and bird’s eye views to enrich a narrative. Camera techniques such as zoom, focus, and depth of field contribute to framing a particular shot. We present an intelligent camera system that automatically positions, pans, tilts, zooms, and tracks events occurring in real-time while obeying traditional standards of cinematography. We design behavior trees that describe how a single intelligent camera might behave from low-level narrative el- ements assigned by “smart events”. Camera actions are formed by hier- archically arranging behavior sub-trees encapsulating nodes that control specific camera semantics. This approach is more modular and particu- larly reusable for quickly creating complex camera styles and transitions rather then focusing only on visibility. Additionally, our user interface allows a director to provide further camera instructions, such as priori- tizing one event over another, drawing a path for the camera to follow, and adjusting camera settings on the fly. We demonstrate our method by placing multiple intelligent cameras in a complicated world with several events and storylines, and illustrate how to produce a well-shot “docu- mentary” of the events constructed in real-time. Keywords: intelligent cameras, behavior trees, camera control, cine- matography, smart events. 1 Introduction Filmmaking is a complex visual medium that combines cinematography and editing to convey a story. The camera must film the right event at the right time to produce the right picture. Cinematography and editing are both complex art forms in their own right, as they involve many highly subjective stylistic decisions. Given the opportunity to shoot the same event, two different directors are likely to produce very different footage with varying shot choices, shot length, and editing techniques. Unfortunately, many games limit a user’s experience to a manually controlled camera, or an automatic camera designed to minimize J.M. Allbeck and P. Faloutsos (Eds.): MIG 2011, LNCS 7060, pp. 156–167, 2011. c  Springer-Verlag Berlin Heidelberg 2011