Image Processing Reference
rare data is one of them. Information can also be either factual or generic. Generic
knowledge can be, for example, a model of the observed phenomenon, general rules,
integrity constraints. Factual information is more directly related to the observations.
Often, these two types of information have different specificities. Generic information
is usually less specific (and serves as a “default”) than factual information, which is
directly relevant to the particular phenomenon being observed. The default is consid-
ered if the specific information is not available or reliable, otherwise, and if the ele-
ments of information are contradictory, more specific information is preferred. Finally,
information can be static or dynamic, and again, this leads to different ways of mod-
eling and describing it.
The information handled in a fusion process is comprised, on the one hand, of the
elements of information we wish to fuse together and, on the other hand, of additional
information used to guide or assist the combination. It can consist of information
regarding the information we wish to combine, such as information on the sources, on
their dependences, their reliability, preferences, etc. It can also be contextual informa-
tion regarding the field. This additional information is not necessarily expressed using
the same formalism as the information we wish to combine (it usually is not), but it
can be involved in choosing the model used for describing the elements of information
we wish to fuse.
One of the important characteristics of information in fusion is its imperfection,
which is always present (fusion would otherwise not be necessary). It can take differ-
ent forms, which are briefly described below. Let us note that there is not always a
consensus on the definition of these concepts in other works. The definitions we give
here are rather intuitive and well suited to the problem of fusion, but are certainly not
universal. The different possible nuances are omitted on purpose here because they
will be discussed further and illustrated in the following chapters for each field of
fusion described in this topic.
Uncertainty. Uncertainty is related to the truth of an element of information and
characterizes the degree to which it conforms with reality [DUB 88]. It refers to the
nature of the object or fact involved, its quality, its essence, or its occurrence.
Imprecision. Imprecision involves the content of the information and therefore is
a measurement of a quantitative lack of knowledge on a measurement [DUB 88]. It
involves the lack of accuracy in quantity, size, time, the lack of definition on a proposal
which is open to different interpretations or with vague and ill-defined contours. This
concept is often confused with uncertainty because both these imperfections can be
present at the same time and one can cause the other. It is important to be able to
tell the difference between these two terms because they are often antagonistic, even
if they can be included in a broader meaning for uncertainty. On the contrary, other
classifications with a larger number of categories have been suggested [KLI 88].