Research On THz Imaging And Image Processing Algorithms

Terahertz(THz,lTHz=1012Hz) wave is a kind of electromagnetic wave with a frequency range from 0.1 THz to 10 THz which is between the frequency of microwave and infrared. It has many properties of transient, lower energy, broadband and penetration, which makes it has broad application prospects in the field of explosives detection, military communication security inspection, medical human body imaging and so on.Terahertz imaging technology, as an important research direction, has attracted a large number of scholars to study and has achieved rapid developments. However, due to the limitation of THz source, THz detector and circuit system, the image result is easy to have problems of low contrast, uneven image and large background noise, which make the image quality not good.According to the background, this paper has researched on the THz imaging system which is based on the micro bolometer terahertz array detector developed by our laboratory independently. Based on the working principle of each key component of imaging system and the theory of terahertz imaging, this paper analyzes the characteristics of terahertz images and starts the study of terahertz imaging preprocessing, designs and implements a set of terahertz imaging system. Specific research contents are as follows:(1) By consulting the literature and materials about the THz field, the working principle of THz source and THz detector are studied. The transmission characteristics of terahertz wave in imaging are analyzed. Based on the theory above, this paper analyzes the influence factors of THz imaging and THz image characteristics.(2) According to the characteristics of the THz image, the image preprocessing is performed in three steps including nonuniformity correction, blind pixel compensation and image enhancement. Nonuniformity correction is based on the calibration method.In blind element compensation, firstly, the blind element is judged according to the response and noise of the detector. Then the method of replacing adjacent pixels is used.For image enhancement, by combining the linear stretching and histogram equalization,an image enhancement algorithm based on the weight distribution is proposed, which overcames the tensile distortion owing to the changes of detector status.(3) The THz imaging system is designed and built, which includes four components: optical system, circuit system, data acquisition system and PC software.And the Camera Link protocol is used in the data acquisition system to ensure the stability of high-speed data transmission. The PC software uses the MFC and Dalsa’s Sapera LT to realize software interface and acquisition and control functions.(4) The THz imaging system is verified and the feasibility of THz imaging system is verified. It lays a solid foundation for the practical application of THz technology.