An overview of the technologies for the real-time mixing of real and virtual images for live TV production is presented. On-set visualization in film production has much in common with this application area; it aims to generate a view of the scene, including virtual elements, in real-time, to help the production crew in tasks such as shot framing. A short review is presented of how some techniques developed for TV have been applied to film. A related area is pre-visualization, where computer graphics are used to simulate a view of a scene before any shooting takes place. Pre-visualization is already applied extensively in film production, but in TV production the traditional tools of paper-based storyboards and cardboard models of a set are still in common use. An example of a tool that provides an intuitive way of planning and visualizing a production is briefly described, which is applicable to both TV and film.