The categorical distribution (figure 3.3) is a discrete distribution that determines
the probability of observing one of K possible outcomes. Hence, the Bernoulli
distribution is a special case of the categorical distribution when there are only two
outcomes. In machine vision the intensity data at a pixel is usually quantized into
discrete levels and so can be modeled with a categorical distribution. The state of
the world may also take one of several discrete values. For example an image of a
vehicle might be classified into {car,motorbike,van,truck} and our uncertainty over
this state could be described by a categorical distribution.
