Keywords: 
• terahertz imaging /
• edge recognition /
• circular template /
• erosion and dilation algorithm

Abstract: An automatic recognition algorithm was proposed for recognizing objects concealed on the edge of human body in an image, which was scanned by THz human security system. First, the pretreatment methods, with binarization, filtering, filling, and morphological corrosion and expansion operations, were used to transfer the original THz image into a binary image, whose outline coordinates was later extracted by clockwise contour tracking algorithm. Then, the combinative application of circular template detection and non-minimal, non-maxima suppression algorithm were applied to calculate and select out all the convex and concave points in the extracted profile coordinates. Finally based on the grouping features of these adjacent convex and concave points, together with their distance constraints, the recognition of the edge objects(Objects covered the contour of human, etc.) could be realized. The experimental results, of testing 500 images of different people with different objects hiding on different edge position taking by the THz human security system, show that this algorithm represents quick identification and strong robustness, having the distinct advantages of strong anti-noise ability, high recognition speed and precision, and also it can match well the recognition accuracy of security system to achieve the system's resolution limit by adjusting proper parameters of the algorithm.