An adaptive search method in feature vector space which can quickly search the
feature vector space indexed based on approximation for a feature vector having
features similar to a query vector according to a varying distance measurement
is provided. The adaptive search method includes the steps of (a) performing a
similarity measurement on a given query vector within the feature vector space,
and (b) applying search conditions limited by the result of the similar measurement
obtained in the step (a) and performing a changed similarity measurement on the
given query vector. According to the adaptive search method, the number of candidate
approximation regions is reduced during a varying distance measurement such as
an on-line retrieval, which improves the search speed.
