Wolfgang Müller, David McG. Squire, Henning
Müller and Thierry Pun,
Hunting moving targets: an extension to Bayesian methods
in multimedia databases.
Tech. Rep. 99.03, Computer Vision Group, Computing Centre, University
of Geneva, rue Général Dufour, 24, CH-1211 Genève,
Switzerland, July 1999.
It has been widely recognised that the difference between
the level of abstraction of the formulation of a query (by example) and
that of the desired result (usually an image with certain semantics)
calls for the use of learning methods that try to bridge this gap. Cox
et al. have proposed a Bayesian method to learn the user's
preferences during each query.
Cox et al.s system, PicHunter, is designed for
optimal performance when the user is searching for a fixed target
image. The performance of the system was evaluated using target
testing, which ranks systems according to the number of interaction
steps required to find the target, leading to simple, easily
reproducible experiments.
There are some aspects of image retrieval, however, which are not
captured by this measure. In particular, the possibility of query
drift (i.e. a moving target) is completely ignored. The algorithm
proposed by Cox et al. does not cope well with a change of
target at a late query stage, because it is assumed that user
feedback is noisy, but consistent.
In the case of a moving target, however, the feedback is noisy
and inconsistent with earlier feedback.
In this paper we propose an enhanced Bayesian scheme which
selectively forgets inconsistent user feedback, thus enabling both
the program and the user to ``change their minds''. The
effectiveness of this scheme is demonstrated in moving target tests
on a database of heterogeneous real-world images.