Abstract
This chapter looks at the technology involved in the mixing of 3D graphics with broadcast video in real time. This is essentially the application of augmented reality techniques in the context of TV production. Examples of the use of this technology include virtual graphics used for presenting election results, and graphics overlaid on a sports pitch to indicate distances. Whilst similar techniques are commonly used in films, these often require extensive post-production; this chapter focuses specifically on approaches that can be used live, which is a common requirement for TV, particularly in news and sport.
Following a brief review of the history of virtual graphics in TV, the technology used in each stage of the production process is examined, starting with the camera and lens. Some of the important characteristics of broadcast video are discussed, and the need for lens calibration is explained. To maintain accurate alignment of the virtual graphics and the real scene, the motion of the camera must be tracked accurately, and methods for achieving this are reviewed. The requirements for high-quality rendering of graphics are then discussed, looking particularly at the differences from rendering for applications such as computer games. The process of keying graphics into an image using chroma-key is then examined in detail. It can be difficult for actors or presenters to work with virtual objects in a studio, unless there is some way for them to see what is going on, so methods of providing visual feedback are presented. Some specific issues related to the use of virtual graphics for sports are then discussed, including methods for tracking camera motion and keying graphics onto areas such as grass or sand. The chapter concludes with a short discussion of an alternative approach to combining graphics and live action, in which graphical representations of real objects and people are created from live video, and placed into a 3D model, allowing the scene to be rendered from a viewpoint that is not tied to the location of the camera.