Motion

A lot of information can be extracted from time varying sequences of images, often more easily than from static images. For example, camouflaged objects are only easily seen when they move. Moreover, the relative sizes and position of objects are more easily determined when the objects move. Even simple image differencing provides an edge detector for the silhouettes of texture-free objects moving over any static background.

The analysis of visual motion divides into two stages:

• the measurement of the motion, and
• the use of motion data to segment the scene into distinct objects and to extract three dimensional information about the shape and motion of the objects.

There are two types of motion to consider: movement in the scene with a static camera, and movement of the camera, or ego motion. Since motion is relative anyway, these types of motion should be the same. However, this is not always the case, since if the scene moves relative to the illumination, shadow effects need to be dealt with. Also, specularities can cause relative motion within the scene. For this lecture, we will ignore all such complications.