Browsing by Author "Tsang, Peter"

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    Complex Fresnel hologram display using a single SLM
    Liu, J. Ping; Hsieh, W. Y.; Poon, Ting-Chung; Tsang, Peter (Optical Society of America, 2011-12-01)
    We propose a novel optical method to display a complex Fresnel hologram using a single spatial light modulator (SLM). The method consists of a standard coherent image processing system with a sinusoidal grating at the Fourier plane. Two or three position-shifted amplitude holograms displayed at the input plane of the processing system can be coupled via the grating and will be precisely overlapped at the system's output plane. As a result, we can synthesize a complex hologram that is free of the twin image and the zero-order light using a single SLM. Because the twin image is not removed via filtering, the full bandwidth of the SLM can be utilized for displaying on-axis holograms. In addition, the degree of freedom of the synthesized complex hologram display can be extended by involving more than three amplitude holograms. (C) 2011 Optical Society of America
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    Computer generation of binary Fresnel holography
    Tsang, Peter; Poon, Ting-Chung; Cheung, W. K.; Liu, J. Ping (Optical Society of America, 2011-03-01)
    Binarization of Fresnel holograms by direct thresholding based on the polarity of the fringe pattern is studied. It is found that if the hologram is binarized (i.e., for black and white hologram pixels) in this manner, only the edges of the object are preserved in the reconstructed image. To alleviate the errors caused by binarization, the use of error diffusion has been routinely employed. However, the reconstructed image using such standard technique is heavily contaminated with random noise. In this paper, we propose a novel noniterative method for generating Fresnel holograms that are suitable for binarization. Our method is capable of preserving good visual quality on the reconstructed images. (C) 2011 Optical Society of America
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    Fast generation of Fresnel holograms based on multirate filtering
    Tsang, Peter; Liu, J. Ping; Cheung, W. K.; Poon, Ting-Chung (Optical Society of America, 2009-12-01)
    One of the major problems in computer-generated holography is the high computation cost involved for the calculation of fringe patterns. Recently, the problem has been addressed by imposing a horizontal parallax only constraint whereby the process can be simplified to the computation of one-dimensional sublines, each representing a scan plane of the object scene. Subsequently the sublines can be expanded to a two-dimensional hologram through multiplication with a reference signal. Furthermore, economical hardware is available with which sublines can be generated in a computationally free manner with high throughput of approximately 100M pixels/second. Apart from decreasing the computation loading, the sublines can be treated as intermediate data that can be compressed by simply downsampling the number of sublines. Despite these favorable features, the method is suitable only for the generation of white light (rainbow) holograms, and the resolution of the reconstructed image is inferior to the classical Fresnel hologram. We propose to generate holograms from one-dimensional sublines so that the above mentioned problems can be alleviated. However, such an approach also leads to a substantial increase in computation loading. To overcome this problem we encapsulated the conversion of sublines to holograms as a multirate filtering process and implemented the latter by use of a fast Fourier transform. Evaluation reveals that, for holograms of moderate size, our method is capable of operating 40,000 times faster than the calculation of Fresnel holograms based on the precomputed table lookup method. Although there is no relative vertical parallax between object points at different distance planes, a global vertical parallax is preserved for the object scene as a whole and the reconstructed image can be observed easily. (C) 2009 Optical Society of America
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    Holographic video at 40 frames per second for 4-million object points
    Tsang, Peter; Cheung, W. K.; Poon, Ting-Chung; Zhou, C. (Optical Society of America, 2011-08-01)
    We propose a fast method for generating digital Fresnel holograms based on an interpolated wavefront-recording plane (IWRP) approach. Our method can be divided into two stages. First, a small, virtual IWRP is derived in a computational-free manner. Second, the IWRP is expanded into a Fresnel hologram with a pair of fast Fourier transform processes, which are realized with the graphic processing unit (GPU). We demonstrate state-of-the-art experimental results, capable of generating a 2048x2048 Fresnel hologram of around 4 x 10(6). object points at a rate of over 40 frames per second. (C) 2011 Optical Society of America
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    Low-bit-rate computer-generated color Fresnel holography with compression ratio of over 1600 times using vector quantization Invited
    Tsang, Peter; Cheung, K. W. K.; Poon, Ting-Chung (Optical Society of America, 2011-12-01)
    We propose a method for compressing a digital color Fresnel hologram based on vector quantization (VQ). The complex color hologram is first separated into three complex holograms, each representing one of the primary colors. Subsequently, each hologram is converted into what we call a real Fresnel hologram and compressed with VQ based on a universal codebook. Experimental evaluation reveals that our scheme is capable of attaining a compression ratio of over 1600 times and still preserving acceptable visual quality on the reconstructed images. Moreover, the decoding process is free from computation and highly resistant to noise contamination on the compressed data. (C) 2011 Optical Society of America
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    Sectioning with edge extraction in optical incoherent imaging processing
    Zhang, Yaping; Wang, Rende; Tsang, Peter; Poon, Ting-Chung (2020-04-15)
    Employing a single-pixel digital holographic recording technique called optical scanning holography (OSH), we accomplish the formidable task of sectioning with edge extraction in three-dimensional (3D) optical incoherent imaging. OSH is a special variant of generalized two-pupil heterodyning image processing, where one of the pupils used is a delta function with the other being a uniform function. In this study, we investigate the use of an annular pupil and a random-phase pupil for edge extraction during sectioning of a 3-D object. Novel simulation results indicate excellent edge extraction of a multi-section object with good sectioning capability, i.e., with each focused edge-extracted section out-of-focused haze has been eliminated. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement