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Creating an Event-Driven Cinematic Camera, Part Two


January 10, 2003 Article Start Previous Page 3 of 3
 

Lights, Camera, Action: The Cinematographer

Last month, we covered the math necessary to turn a description of a shot into actual camera position and orientation. This month, we will build on that and flesh out the role of the cinematographer by covering the handling of transitions.

The simplest transition is the cut, where we only need to change the camera position and orientation to a new position and orientation. Only slightly more complex is the fade, which provides a two-dimensional visual effect between two camera views. When fading, it is important to decide whether to fade between two static images or allow the world to continue to simulate while the fade occurs. Allowing continued simulation implies rendering two scenes per frame but eliminates the need for pauses in gameplay. If you are able to handle the extra rendering, interesting fade patterns can be achieved by using complementary masks when rendering each scene. Depending on the hardware available for rendering, you may only be able to do black and white masks, or you could go all the way to alpha-value masks.

The other group of transitions involves moving the camera. The three transitions we will consider are pan, zoom, and crane. The decision of which move to make depends on the camera and focal positions for the two shots. Figure 2 shows the various situations that lead to the choice of a particular shot. The pan is used if the camera is in approximately the same location for both shots and only the focal point moves. Though this happens rarely in an interactive environment, when it does happen the old camera position can be kept and only the orientation needs to be animated to the new orientation. Similarly, the conditions for zooming are fairly uncommon, as both the camera positions and focal points must lie close to the same line, but when it does occur the camera field-of-view can be used to allow a much more interesting transition than a simple camera move.


Figure 2. Shot transition criteria, where re is the radius of acceptable error.

Finally, we come to the most complex transition, the crane. The best method for creating a crane move is often by borrowing the services of the AI’s path-planning algorithm in order to avoid moving the camera through objects. It is best if the path planning also handles orientation, as this will lead to better results than interpolating between the focal points.

Unfortunately, getting crane shots to look their best is a complex process for which this is only a starting point. If you do not have the time to invest in making them work, you may wish to leave them out altogether.

Beyond the Basics

You now have enough information to create your own basic cinematic system to include in your game. There is plenty of room to go beyond this basic system. Research on some of these areas has already been conducted in academic circles. For instance, events that involve conversations between characters could be specified as a single suggestion rather than manually suggesting each individual shot during the discourse. “The Virtual Cinematographer” and “Real-time Cinematic Camera Control for Interactive Narratives” (see For More Information) describe how director styles can be created to specify camera shots automatically for these situations. This reduces human involvement, which is always important as it allows other features to be added to the game.

Another important aspect of cinematography that is only now becoming possible with the power of newer graphics hardware is depth-of-field. This is often used as a mechanism to draw attention to various elements in a scene of a film. As rendering of depth-of-field becomes more common, it will be important to develop controls for it that are based on the principles learned from cinematography. It is even possible to extend the concept of depth-of-field in ways that would be difficult in real-world filmmaking. “Semantic Depth of Field” in For More Information talks about selective application of depth-of-field effects on important elements of an image.

As you can see, there is a wealth of information out there and plenty of room for experimentation and new ideas. As games continue to grow in popularity, they must meet the demands of the more general audience that is used to the conventions of films. There is much to do in order to reach this goal and continue to expand the scope of game development. Continued innovation and experimentation in this area will bring out greater variety of expression on the part of game developers, and richer, more compelling game experiences for players.

 

For More Information

Amerson, Daniel, and Shaun Kime. “Real-time Cinematic Camera Control for Interactive Narratives.” American Association for Artificial Intelligence, 2000. pp. 1–4.

Arijon, Daniel. Grammar of the Film Language. Los Angeles: Silman-James Press, 1976.

He, Li-wei, Michael F. Cohen, and David H. Salesin. “The Virtual Cinematographer: A Paradigm for Automatic Real-Time Camera Control and Directing.” Proceedings of SIGGRAPH 1996. pp. 217–224.

Katz, Steven D. Film Directing Shot by Shot. Studio City, Calif.: Michael Wiese Productions, 1991.

Kosara, Robert, Silvia Miksch, and Helwig Hauser. “Semantic Depth of Field.” Proceedings of the IEEE Symposium on Information Visualization 2001.

Lander, Jeff. “Lights… Camera… Let’s Have Some Action Already!” Graphic Content, Game Developer vol. 7, no. 4 (April 2000): pp. 15–20.

 

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