Background subtraction is a method for identifying moving objects against a
static background. Although there are many variations on the theme, the basic
idea is to
1. estimate the pixel properties of the static background,
2. subtract actual pixel values from the background estimates, and
3. assume that if the difference exceeds a given threshold that the pixel must
be part of a moving object.
Normally one follows the last step by forming connected components, or blobs,
of moving pixels that correspond to the moving objects. Factors that confound
background subtraction include background motion, moving objects that are
similar in appearance to the background, background variations over long periods
of time, and objects in close proximity merging together. In general, the