Passive millimeter wave imaging and analysis for concealed object detection

Passive millimeter wave imaging has the capability of detecting concealed objects under clothing. However, the image quality is often degraded due to low spatial resolution and low signal level. This paper addresses passive millimeter wave imaging and registration and fusion of a passive millimeter and a visual image in order to visualize human subject's identity and concealed objects together. The image registration process is composed of body boundary detection and affine transform maximizing cross-correlation coefficients of two edge images. The image fusion process comprises three stages: discrete wavelet transform for image decomposition, a fusion rule for merging the coefficients, and the inverse transform for image synthesis. In the experiments, metallic and non-metallic objects are detected and fused with the image of a human subject.