| ISLE | Chapter 7
| Motion Parallax
Motion parallax is a monocular depth cue arising from the relative velocities of objects moving across the retinae of a moving person. The term parallax refers to a change in position. Thus, motion parallax is a change in position caused by the movement of the viewer. Motion parallax arises from the motion of the observer in the environment. It is perhaps easier to think of what motion parallax is by imagining yourself as a passenger in a car looking out the side window. The car is moving very fast down the highway. The objects very close to the window, such as the small trees planted by the highway, seem to rush by. Beyond the small trees, you can see a distant farmhouse. The farmhouse appears to move more slowly relative to you in the car. You know that the trees and the farmhouse are standing still; you are the object that is moving.You can observe this phenomenon in the video below. This video shows clouds moving by a plane. The closer the cloud to the plane, the faster it appears to move.
In this activity, you can create objects, in this case circles, that will move as they might with different speeds that simulate the different motions that you might experience in motion parallax. See if the slower circle does not appear to be farther away. You can also add and subtract different pictorial depth cues and see how they contribute to the perception of depth in addition to motion parallax.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On the Illustration tab, you can adjust these parameters:
Animate: Select this check box to start the motion of the dots.
You can select from the following pictorial depth cues
(select them by clicking or pressing the cue to activate the checkbox):
Relative Height: causes red dot to move down, and blue dot to move has as far
simulated diferent relative heights.
Relative Size: changes the size of the blue and red circles to simulate
being farther away.
Texture Gradient: Add a gradient that can indicate a receding area.
Shadow: Add a shadow to the blue and red to simulate that they are off
of the screen.
Atmospheric Perspctive: Add a blur and bluish haze to the blue and red circles to
simulate the affect of the atmosphere.
Depth: Adjust the degree of each of the pictorial depth cues to make the objects
appear closer or farther.
Pressing this button restores the settings to their default values and allows you to adjust speed and relative size. It also resets the counter before you can indicate if you have the objects arriving at the same time.