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Section: New Results

Interactive Virtual Cinematography

Participants : Marc Christie [contact] , Christophe Lino.

The domain of Virtual Cinematography explores the operationalization of rules and conventions pertaining to camera placement, light placement and staging in virtual environments. In 2012, we have tackled two key issues in relation to the reactive control of virtual cameras: (i) the design of an efficient occlusion-free target tracking technique in dynamic environments and (ii) the design of a novel composition technique based on a 2D-manifold representation of search space.

The first issue is related to maintaining the visibility of target objects, a fundamental problem in automatic camera control for 3D graphics applications. Practical real-time camera control algorithms generally only incorporate mechanisms for the evaluation of the visibility of target objects from a single viewpoint, and idealize the geometric complexity of target objects. Drawing on work in soft shadow generation, we perform low resolution projections, from target objects to rapidly compute their visibility for a sample of locations around the current camera position. This computation is extended to aggregate visibility in a temporal window to improve camera stability in the face of partial and sudden onset occlusion. To capture the full spatial extent of target objects we use a stochastic approximation of their surface area. Our implementation is the first practical occlusion-free real-time camera control framework for multiple target objects. The result is a robust component that can be integrated to any virtual camera control system that requires the precise computation of visibility for multiple target (see [20] ).

The second challenge is related to the automatic positioning a virtual camera in a 3D environment given the specification of visual properties to be satisfied (on-screen layout of subjects, vantage angles, visibility) is a complex and challenging problem. Most approaches tackle the problem by expressing visual properties as constraints or functions to optimize, and rely on computationally expensive search techniques to explore the solution space. We have shwon how to express and solve the exact on-screen positioning of two or three subjects by expressing the solution space for each couple of subjects as a 2D manifold surface [23] . We demonstrate how to use this manifold surface to solve Blinn's spacecraft problem with a straightforward algebraic approach. We extend the solution to three subjects and we show how to cast the complex 6D optimization problem tackled by most contributions in the field in a simple 2D optimization on the manifold surface by pruning large portions of the search space. The result is a robust and very efficient technique which finds a wide range of applications in virtual camera control and more generally in computer graphics.

We have also explored the application of automated editing techniques to Machinema [19] .

Besides we have been involved in the process of rendering camera motions (from real movies) using haptic devices (a joint work with Technicolor and VR4i, accepted at VRST 2012 [21] ), and have authored a state of the art report on Haptic Audiovisual (published in Transactions on Haptics [8] ).