Viola [] has developed a way3.17 of finding and measuring the similarity between two images or more
by repeatedly comparing pairs of images. This ability to compare images
is crucial for registration of images as it robustly and accurately
returns an estimate of the beneficialness of the warps applied. Chapter
deals with the introduction of information
theory and some of the basic measures which can explain the following
in more detail. However, it is the principle that is worth understanding
at this stage, rather than tedious technicality [,].
Mutual information [WWW-13] computes volumes of overlap
in images. If two images are matched, the joint histogram is then
expected to give an indication of where sharp grey-value peaks
are located and the sharpness value of these peaks. Under the converse
case which is mis-registration, the joint histogram is then expected
to show peaks of low sharpness and new peaks can emerge. The algorithms
and advanced information theoretic expressions that take advantage
of this observation are at this stage left out entirely. At this point,
it is only worth defining a joint information (or entropy) to be
and state that MI calculates
. This means that
joint information is subtracted from the sum of information present
in the two individual images.