Secrets of Screen Direction and Continuity of Motion

a cameraman bending over a camera focusing and framing a shot

One of the coolest things about television, film and video production is the way that camera angles can alter the viewer’s perception of reality. This is particularly true in the case of continuity of motion and screen direction. Understanding how camera position impacts screen direction is important for two reasons: so producers can harness this knowledge to create compelling and believable sequences, and, even more importantly, to avoid making mistakes that might unintentionally create confusion.

Screen Direction
When shooting a video sequence of a person walking, running, biking, driving or otherwise travelling from one location to another, the direction the subject moves across the screen is far more important than the direction the subject actually travels in the real world. In fact, continuity of motion has very little to do with the direction a subject actually moves. Video producers must always be mindful of the fact that continuity of motion is all about the position of the camera in relation to a moving subject. Depending on where the video camera is positioned, a subject who is actually walking in a straight line can appear to change direction, and a person walking in various directions can appear to walk in a straight line. Confused? Keep reading. It will all make sense in a few paragraph’s time. 

Illustration of a line drawn between a person walking and a camera
Left, Right, Left

In order to illustrate, imagine a video production in which a drum majorette marches along the yellow dividing line in the middle of Main Street. In real life our marching majorette will walk 20 steps from South to North. Imagine also that Main Street is lined on both the East and West sides by sidewalks that run parallel to the street. With the video camera positioned on the sidewalk on the West side of the street and aimed back at the majorette, the walking subject enters the right side of the viewfinder, walks across the screen from right to left, then exits the left side of the frame. In this case the subject traveling from South to North crosses the screen from right to left.
example of  someone appearing to be walking in the same direction in three shots in a scene
As shown in our example of a man walking in a park, the video camera can be positioned anywhere on the West side of the line running down the middle of the street and the subject will still travel right to left on screen, and will appear to continue in a consistent direction. We can even position the video camera right on the divided street line with the subject walking directly towards, or away from the camera without compromising the continuity of motion within the production.

Illustration of the camera crosses over to the opposite side of the subject
Crossing the Line

Consider, however, how the production changes if the video camera operator were shooting video from the other side of the street, with the camera on the opposite side of the line pointed back at the subject. The majorette once again marches from South to North. Even though she moves in the same direction in the real world, this time she enters the viewfinder from the left side of the frame, walks from left to right, then exits the right side of the viewfinder.
example of a person walking the opposite direction from the earlier scene
 Our subject travels the same direction in the real world; but the opposite direction on screen. If the two shots were edited together, the marcher would appear to have turned around and gone back the way from which she or he came.

The Action Axis

In this example, the yellow line painted down the middle of the roadway represents what production professionals refer to as the action axis. The action axis is not typically a visible and tangible line like the yellow stripe on our hypothetical road, but is instead an invisible barrier that runs through a moving subject and stretches on to infinity along the course the subject travels, separating a scene into two hemispheres. To maintain consistency of screen direction, the video camera operator must merely shoot all shots from the same side of the action axis. As long as the video camera stays on the same side of the subject, you will maintain consistent screen direction regardless of the actual direction your subject walks in the real world. Got it? Good.
North, East, South & West
Now, imagine that the majorette were to march all the way around the block, starting by walking to the North, then turning East, South and finally West so she ended up exactly where she began. If the video camera were repositioned as she walked, shooting first from West pointed East, then from North pointed South, East pointed West and finally South pointed North, without crossing the action axis, the marching majorette would always enter from screen right, walk across the screen from right to left, and exit screen left. So even though she would have actually traveled in four different directions, to the viewer she would appear to have walked in a long straight line.
The secret to shooting video sequences without compromising continuity of motion is to remain mindful — not of travel direction — but of screen direction. Maintaining screen direction in your video is a matter of relativity, not of reality.
Chuck Peters is a 3-time Emmy Award Winning Producer, Director, Writer and Host.
Cameraperson Image from Shutterstock

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Tue, 02/18/2014 - 4:38am



TimGreig's picture

Either I'm completely confused or the example text or images are wrong. In the first example the subject as described enters screens from LEFT and leaves right. Not the other way around. Which then makes the change of camera position to the opposite side of the street having them enter from right,go across screen to exit left. It's hard to get this continuity thing right!