Target versus background characterization: Second generation wavelets and support vector machines

The problem of determining the difference between a target and the background is a very difficult and ill-posed problem, yet it is a problem constantly faced by engineers working in target detection and machine vision. Terms like target, background, and clutter are not well defined and are often used differently in every context. Clutter can be defined as a stationary noise process, anything non-target, or anything that looks like a target but is not. Targets can be defined by deformable templates, models, or by specific feature vectors. Models, templates and features must be defined before classification begins. Both models and feature vectors somehow hold the defining characteristics of the target, for example the gun barrel of a tank. Most importantly, feature vectors and models reduce the dimensionality of the problem making numerical methods possible. This paper explores several fairly recent techniques that provide promising new approaches to these old problems. Wavelets are used to de-trend images to eliminate deterministic components, and a trained support vector machine is used to classify the remaining complicated or stochastic components of the image. Ripley's K-function is used to study the spatial location of the wavelet coefficients. The support vector machine avoids the choice of a model or feature vector, and the wavelets provide a way to determine the non-predictability of the local image components. The K-function of the wavelet coefficients serves as a new clutter metric. The technique is tested on the TNO image set through several random simulations.