Method for retrieving sequences of images on the basis of motion analysis

Abstract

This paper describes a method for retrieving sequences of images in a motion image database using motion information as a key. This information is obtained by application of the motion analysis technique. The proposed method has three steps: automatic extraction of motion vectors through frame sequences, motion description using spatio-temporal space, and retrieval of sequences of images. The motion vectors of objects are extracted on the basis of block motion estimation. Block motion estimation tracks each block of a scene throughout a period. This tracking procedure takes account of the traceability of each block and the reliability of its calculated motion vector. Extracted motion vectors are mapped using spatio- temporal space (x-y-t). The motion of each block is represented as one vector in the feature space, and motion vectors in a scene are aggregated into several representative vectors by statistical analysis. The retrieval of sequences of images is divided into two parts: specification of the query conditions, and matching between the query conditions and the motion database. The query conditions are input from a stroke device. The user can interactively manipulate the query conditions, such as the number, period, and starting time of objects. The data are gathered as an x-y series at a given interval, and then normalized. Similarity is defined in spatio-temporal space as the distance between the query conditions and the stored motion index. Candidate sequences of images are ranked in order of distance. An experimental system has been developed for retrieving sequences of images on a workstation.