Automatic two-stage IR and MMW image registration algorithm for concealed weapons detection

A two-stage registration scheme for the concealed weapons detection (CWD) problem is developed. The goal is to automatically register images taken simultaneously from two different (infrared (IR) and millimetre wave (MMW)) but parallel sensors whose lines of sight (LOS) are close to each other. The purpose of the first stage is to register the images coarsely. A feature-based image registration algorithm based on human body silhouettes is developed at this stage. The pose parameters found at this stage are used as the starting search point for the second stage of the registration algorithm. At the second stage, maximisation of the mutual information measure between IR and MMW images is performed to improve the pose parameters obtained at the first stage. Two-dimensional partial volume interpolation is employed to estimate the joint histogram that is needed to calculate mutual information. The simplex search algorithm is utilised to maximise the MI measure. In both stages, the distortion between the two images is assumed to be a rigid body transformation. Experimental results indicate that the automated two-stage registration algorithm performs fairly well.