How Do Detected Objects Affect the Noise Distribution of Terahertz Security Images?

The purpose of this paper is to analyze how detected objects affect the noise distribution of terahertz (THz) security images. Noise in THz image caused by hardware deteriorates the image quality seriously, limiting the application. In addition, there are a few papers on the noise analysis of THz screenings. Due to the special attributes of the THz image compared with the natural image, an alpha-stable distribution is used to fit the noise of THz image instead of the commonly-used Gaussian distribution. The database used in this paper is composed of 181 THz image cubes with a test object as well as two empty image cubes. After analyzing the four parameters of alpha-stable distribution, we can observe that the noise patterns of THz images are indeed different from those of natural image obtained by RGB camera. The possible reasons are given based on the principles of the THz imaging device. The analysis of the distribution of four parameters of alpha-stable model demonstrates that there exists a nonlinear effect due to the change of reflected wave's pattern caused by the body structure. This paper provides an efficient and flexible model for THz images and a useful guidance for the design of THz image denoising algorithms and the development of imaging hardware.