|Title:||Imaging techniques with a single-pixel detector and their applications|
|Advisors:||Chen, Wen (EIE)|
Yu, Changyuan (EIE)
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Electronic and Information Engineering|
|Pages:||xxii, 148 pages : color illustrations|
|Abstract:||The investigation of imaging techniques is of great significance for various applications, e.g., non-destructive testing and biological imaging. In many conventional optical imaging techniques, 2D charge-coupled device (CCD) is usually used for the recording. Although CCD camera can be applied for the imaging in various environments, there are still a number of limitations in practice which can restrict its applications. For instance, in scattering environments the scattered light imposes significant effect, which might lead to a poor performance in recovering high-quality objects. In addition, under conditions of low light the data recorded by CCD camera could not be sufficient or effective for high-quality object reconstruction, and under conditions of non-visible wavebands CCD camera might be even unavailable. In order to resolve the problems existing in many conventional imaging techniques, single-pixel imaging (SPI) has emerged as a promising technique to extract object information by using a single-pixel detector (called single-pixel bucket detector). Different from CCD camera with spatial resolution, single-pixel detector employed in the SPI is a non-spatially resolving detector. The SPI techniques have been rapidly developed over the past decades. Aside from the applications integrated with many conventional optical systems, it has also been demonstrated that the SPI can be applied in complex environments, e.g., turbulent atmosphere. However, there are still some significant challenges which need to be further overcome in the SPI field, e.g., imaging quality, sampling efficiency and applications in complex environments. This thesis is to develop new techniques to resolve fundamental problems and address application concerns in the SPI. In this thesis, to achieve high imaging quality using a small number of measurements, a Fourier spectrum retrieval method is developed in the SPI. In the proposed method, some low-frequency Fourier spectrum coefficients are first calculated directly by using a small number of measurements, and then the proposed method enables retrieval of high-frequency Fourier spectrum coefficients by using the calculated low-frequency coefficients. The results and analyses fully demonstrate feasibility and effectiveness of the proposed method in the SPI. In order to improve sampling efficiency in the SPI, a single-step measurement method is also proposed to retrieve Hadamard spectrum coefficients. In contrast with conventional differential methods, the proposed single-step measurement method effectively reduces the number of measurements, and can retrieve the objects with the same quality as that obtained by using conventional methods. It is further demonstrated that the retrieved object information can be fully invisible when a small number of randomly-selected Hadamard spectrum coefficients are applied in the SPI. This property is further applied for object authentication using the SPI.|
Single-pixel ghost holography method is also proposed, and its application for optical security is further demonstrated which can dramatically enrich optical security field. The numerical analyses and optical experimental results fully demonstrate feasibility and effectiveness of the proposed method. Finally, object authentication is studied in scattering media by using structured-detection-based techniques in the SPI for optical security. The proposed optical authentication methods significantly enrich the applications of SPI, and can be flexibly applied in practice to enhance system complexity for optically securing information. In addition, phase-only authentication through scattering media using single-pixel digital holography is further carried out and verified by using optical experimental results. The studies presented in this thesis effectively resolve fundamental problems and address application concerns in the SPI. The work presented in this thesis can contribute to better understand the SPI, and could shed some light on the further development of the SPI and practical applications of the SPI.
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