Length-speed ratio (LSR) as a characteristic for moving elements real-time classification

In this article, the length–speed ratio (LSR) is proposed as a basic characteristic for the real-time detection of moving objects. We define the LSR of a uniform moving zone as the relation between its length in the direction of motion and the speed of this motion. For a given zone of the image with uniform gray level (or patch), the greater its length in the direction of motion and the smaller its speed, the greater its LSR. A moving element is generally composed of various zones of uniform gray levels (or patches), which move with the same speed but which have different lengths in the direction of motion and which therefore have a characteristic set of LSR values. In this article, this ‘‘LSR footprint’’ is proposed as the basic characteristic for the detection and subsequent classification of moving elements in image sequences. The problem of detecting a moving element in a sequence of images is transformed into the recognition of a pattern on a static image, namely the LSR footprint. We also specify how to obtain this characteristic in real time, we discuss its invariants and we consider the cases for which LSR detection of movement is applicable. We also present its use in some significant examples and we compare it with other methods applicable to similar computational problems. r 2003 Elsevier Science Ltd. All rights reserved.