Shots that accentuate the illusion of depth are referred to as deep frames, while shots that flatten the space along the z-axis are called flat frames.
Each type of shot has its own expressive value. The several compositional techniques used to control the perception of depth in the frame are called depth cues.
Figure 1This flat frame from Lucas’ THX-1138 (left) intentionally suppresses indicators that imply depth while Kubrick uses several depth cues for this deep frame in The Shining (right).
- Relative size is the depth cue that arises from the way we judge the sizes of objects in the real world. By their relative size, we judge how far apart they must be in the near and far planes of the frame. In Figure 1, right, the fact that the two little girls are smaller than the boy’s head extends the perception of z-axis space because we understand that, in order to appear so small, they must be far away (in the background) from the boy, who is in the foreground.
- Receding planes is another depth cue in which objects are placed along foreground, midground, and background along the z-axis. In Figure 1, right , the doors and ceiling lamps serve this function.
- Objects overlapping where objects along the z-axis (depth) overlap and partially obstruct each other (foreground details covering background objects) is another strong depth cue. Even a small detail included in the foreground can immediately create a deeper frame.
- Composing your image with receding diagonal lines also provides a powerful depth cue. For example, a row of buildings shot head on will line the horizontal axis of the frame in a flat row, but adjust the camera position left or right so that you’re shooting the row on the diagonal and now they will appear to be receding along the z-axis. The converging diagonal lines in Figure 1, right, provide a very strong indication of depth as they are receding toward a central point.
- Finally, focus can play a crucial role in a viewer’s perception of depth. An image with deep focus allows a viewer to perceive fine detail deep into the frame, extending the significance of the z-axis, while shallow focus flattens the background and isolates limited planes along the z-axis. The capacity to control the range of focus along the z-axis depends on technical aspects of the lens and is a creative tool.