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Browsing by Author "Liu, Jung-Ping"

Now showing 1 - 5 of 5
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    Enhancing the Quality of Sampled Phase-Only Hologram (SPOH) Based on Time-Division Comb Filtering
    Tsang, Peter W. M.; Liu, Jung-Ping; Lam, Hoson; Poon, Ting-Chung (MDPI, 2020-04-15)
    Generation of digital phase-only Fresnel holograms is an important research area in digital holography, as it leads to a substantial simplification of a holographic display system. However, the quality of the reconstructed image of a hologram without the magnitude component is heavily degraded. The problem can be reduced by down-sampling the intensity of an image prior to generating the hologram. The method, referred to as “sampled phase-only hologram” (SPOH) generation, results in reconstructed images that are masked with the pattern of the down-sampling lattice. This paper reports a novel, low complexity method to alleviate this problem through the concept of comb filtering. Results reveal prominent enhancement on the reconstructed image of a SPOH.
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    Fast Extended Depth-of-Field Reconstruction for Complex Holograms Using Block Partitioned Entropy Minimization
    Tsang, Peter Wai Ming; Poon, Ting-Chung; Liu, Jung-Ping (MDPI, 2018-05-21)
    Optical scanning holography (OSH) is a powerful and effective method for capturing the complex hologram of a three-dimensional (3-D) scene. Such captured complex hologram is called optical scanned hologram. However, reconstructing a focused image from an optical scanned hologram is a difficult issue, as OSH technique can be applied to acquire holograms of wide-view and complicated object scenes. Solutions developed to date are mostly computationally intensive, and in so far only reconstruction of simple object scenes have been demonstrated. In this paper we report a low complexity method for reconstructing a focused image from an optical scanned hologram that is representing a 3-D object scene. Briefly, a complex hologram is back-propagated onto regular spaced images along the axial direction, and from which a crude, blocky depth map of the object scene is computed according to non-overlapping block partitioned entropy minimization. Subsequently, the depth map is low-pass filtered to decrease the blocky distribution, and employed to reconstruct a single focused image of the object scene for extended depth of field. The method proposed here can be applied to any complex holograms such as those obtained from standard phase-shifting holography.
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    Incoherent Digital Holography: A Review
    Liu, Jung-Ping; Tahara, Tatsuki; Hayasaki, Yoshio; Poon, Ting-Chung (MDPI, 2018-01-20)
    Digital holography (DH) is a promising technique for modern three-dimensional (3D) imaging. Coherent holography records the complex amplitude of a 3D object holographically, giving speckle noise upon reconstruction and presenting a serious drawback inherent in coherent optical systems. On the other hand, incoherent holography records the intensity distribution of the object, allowing a higher signal-to-noise ratio as compared to its coherent counterpart. Currently there are two incoherent digital holographic techniques: optical scanning holography (OSH) and Fresnel incoherent correlation holography (FINCH). In this review, we first explain the principles of OSH and FINCH. We then compare, to some extent, the differences between OSH and FINCH. Finally, some of the recent applications of the two incoherent holographic techniques are reviewed.
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    Off-axis optical scanning holography [Invited]
    Zhang, Yaping; Yao, Yongwei; Zhang, Jingyuan; Liu, Jung-Ping; Poon, Ting-Chung (Optical Society of America, 2022-02-01)
    Optical scanning holography (OSH) involves the principles of optical scanning and heterodyning. The use of heterodyning leads to phase-preserving, which is the basic idea of holography. While heterodyning has numerous advantages, it requires complicated and expensive electronic processing. We investigate an off-axis approach to OSH, thereby eliminating the use of heterodyning for phase retrieval.We develop optical scanning theory for holographic imaging and show that by properly designing the scanning beam, we can performcoherent and incoherent holographic recording. Simulation results are provided to verify the proposed idea.
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    Performance Estimation of Intensity Accumulation Display by Computer-Generated Holograms
    Liu, Jung-Ping; Lin, Yu-Chih; Jiao, Shuming; Poon, Ting-Chung (MDPI, 2021-08-22)
    The image generated by binary computer-generated holograms (CGHs) always suffers from serious speckle noise. Thanks to the fast frame rate of the binary spatial light modulator, the speckle can be significantly suppressed by intensity accumulation, i.e., the sequential display of multiple CGHs of the same scene. If enough randomness is added to the CGHs, the speckle noise can be mostly averaged out. Intuitively, the quality of the reconstructed image should be proportional to the number of intensity accumulation. However, there is no simple method to predict the dependence of the average noise and accumulation number, and we can only know the results after finishing the full computation. In this paper, we propose an empirical formula of the average noise based on the speckle phenomenon in a laser projector. Using this model, we have confirmed that the randomness induced by random phase is equivalent to that induced by random down-sampling for the generation of binary CGHs. In addition, if the computational efficiency is a concern, the CGH calculated with iterations is not recommended for intensity accumulation display. Finally, there is an upper-quality limit of the reconstructed image by intensity accumulation. Thus, a strategy for efficient intensity accumulation is suggested.