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1.
Appl Opt ; 58(20): 5547-5555, 2019 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-31504026

RESUMO

The error diffusion method can effectively reduce quality degradation by propagating thresholding errors to neighboring pixels in the conversion of a gray-scale hologram to a binary hologram. In previous works, the four weighting coefficients in error diffusion are mostly set as the Floyd-Steinberg coefficient, which was determined empirically and originally proposed for photograph processing. In this work, we point out that the Floyd-Steinberg coefficients can be suboptimal for hologram error diffusion binarization. Furthermore, the weighting coefficients are optimized for each different hologram adaptively. Compared with conventional coefficients, our optimized coefficients can better preserve the fidelity of a reconstructed image after a hologram is binarized.

2.
Appl Opt ; 58(14): 3735-3741, 2019 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-31158183

RESUMO

The direct binary search (DBS) algorithm was originally invented for the synthesis of a binary Fourier hologram, and was applied for the generation of a binary Fresnel hologram recently. DBS performs quality evaluation on every pixel. Therefore, both the quality and diffraction efficiency of the generated binary hologram are better among various algorithms of the binary hologram. However, DBS is a time-consuming algorithm and thus is impractical for the generation of high-definition computer-generated holograms. In this paper, we proposed an enhanced DBS (E-DBS) method to speed up the hologram computation. E-DBS is based on the same pixelwise evaluation strategy of DBS, but the diffraction field of a single pixel is precomputed as a lookup table. In evaluating any pixel value, only a small area in the region of interest affected by the diffraction field of single pixel is calculated. In addition, it is also found that qualified results can be obtained by using only 4% of the area of the diffraction field. As a result, the computing complexity of E-DBS can be reduced by at least 2 orders of magnitude in contrast to conventional DBS.

3.
Appl Opt ; 57(1): A215-A221, 2018 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29328148

RESUMO

In a polygon-based computer-generated hologram (CGH), the three-dimensional (3D) model is represented as a polygon, which consists of numerous small facets. Lighting effect, material texture, and surface property can be included in the polygonal model, which enables polygon-based CGH to realize high-fidelity 3D display. On the other hand, the occlusion effect is an important depth cue for 3D display. In polygon-based CGH, however, occlusion processing is difficult and time-consuming work. In this paper, we proposed a simple and fast occlusion processing method, the slice-by-slice silhouette (S3) method, for generating the occlusion effect in polygon-based CGH. In the S3 method, the polygonal model is sliced into multiple thin segments. For each segment, a silhouette mask is generated and located at the backside of the segment. The incident light is first shaded by the mask and superimposes on the light emitted from the facets of the evaluated segment. In this way, every segment can be processed sequentially to get the resulting object light. Our experimental result demonstrates that the S3 method can generate a high-definition hologram with qualified occlusion effect. The computing complexity of the S3 method is lower than that of previous methods. In addition, the S3 method can be parallelized easily, and thus can be further speeded up by applying a parallel computing framework, such as multi-core CPU or GPU.

4.
Opt Express ; 24(13): 14582-8, 2016 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-27410610

RESUMO

Incoherent digital holography (IDH) can be realized by optical scanning holography or self-interference incoherent holography. Although IDH can exhibit high quality reconstruction due to its inherently speckle-free property, direct display of an incoherent hologram is a challenge because of its amplitude nonlinearity and the demand of complex modulation. In this paper we propose to compensate the amplitude nonlinearity at the object plane, and use bidirectional error-diffusion method to convert the complex-type incoherent Fresnel hologram to a phase-only Fresnel hologram for display. A spatial light modulator is used to reconstruct the phase-only hologram optically to demonstrate the validity of our proposed method.

5.
Opt Lett ; 40(10): 2366-9, 2015 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-26393741

RESUMO

In optical scanning holography (OSH), the coherence properties of the acquired holograms depend on the single-pixel size, i.e., the active area of the photodetector. For the first time, to the best of our knowledge, we have demonstrated coherent, partial coherent, and incoherent three-dimensional (3D) imaging by experiment in such a single-pixel digital holographic recording system. We have found, for the incoherent mode of OSH, in which the detector of the largest active area is applied, the 3D location of a diffusely reflecting object can be successfully retrieved without speckle noise. For the partial coherent mode employing a smaller pixel size of the detector, significant speckles and randomly distributed bright spots appear among the reconstructed images. For the coherent mode of OSH when the size of the pixel is vanishingly small, the bright spots disappear. However, the speckle remains and the signal-to-noise ratio is low.

6.
Appl Opt ; 54(1): A59-66, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25967023

RESUMO

In optical scanning holography (OSH), the system can be operated in coherent mode by using a pinhole detector, or in incoherent mode by using a spatially integrating detector. In the coherent mode, the three-dimensional (3D) amplitude transparency of an object is recorded and thus the phase of the object can be retrieved. On the other hand, it is the 3D intensity transparency of the object recorded in the incoherent mode and thus the speckle can be suppressed. OSH in both coherence modes has been well investigated. However, there is no discussion on the case between the coherent mode and incoherent mode, namely, the partial-coherent mode. In this paper, we derived for the first time, to the best of our knowledge, the formula of OSH in various modes of coherence. We found the detector in OSH plays the role of a kind of filter for the field. The retrieved amplitude transparency of the object is thus nonlinearly processed by the mask function of the detector. Consequently, the reconstructed image cannot benefit from the implementation of the partial-coherent mode. On the contrary, significant artifacts usually appear among the reconstructed image and thus the image quality degrades.

7.
Appl Opt ; 54(1): DH1-2, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25967030

RESUMO

The OSA Topical Meeting "Digital Holography and 3D Imaging (DH)" was held in Seattle, Washington, 13-17 July 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. In this year (2014), Optics Express (OE) and AO jointly decided to have one such feature issue in each journal. The feature issue includes 27 papers and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The DH meeting will continue in the future, as expected, and the next meeting is scheduled to be held on 24-28 May 2015, at Shanghai Institute of Optics and Fine Mechanics, Shanghai, China.

8.
Appl Opt ; 54(14): 4447-52, 2015 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-25967500

RESUMO

A high-axial-resolution, full-field optical coherence microscope (FFOCM) for topography and tomography applications is presented. The FFOCM is based on a polarization Linnik interference microscope equipped with a tungsten halogen lamp. The phase difference between the reference and test beams in the microscope is precisely and quickly shifted by using an achromatic liquid-crystal phase shifter (LCPS). The cross-sectional amplitude and phase maps of an interferogram are retrieved by using a three-step phase-shifting technique. The LCPS consists of three identical nematic liquid-crystal (NLC) cells sandwiched between two quarter-wave plates so that it functions as a typical quarter-half-quarter phase shifter. Instead of using high-cost NLC cells with precise thickness of half-wave retardation, a method is proposed to operate thicker NLC cells without scarifying the axial resolution. Experimental results reveal that the FFOCM is able to perform three-dimensional micrometer-resolution imaging.

9.
Appl Opt ; 53(4): 756-63, 2014 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-24514194

RESUMO

In computer-generated Fresnel holography, direct sampling (DS) and simple shading (SS) are two common ways to generate sampled Fresnel zone plates (FZPs) on the hologram plane. Nevertheless, either aliasing or vignetting, or both, will occur in the reconstructed image when the DS method or the SS method is applied. To avoid vignetting together with aliasing in the two sampling methods, either the object size or the object distance must be restricted in generating the holograms. In this paper we propose a mask-shifting (MS) method to generate the sampled FZPs. The main concept of the MS method is that the center of the FZP can be shifted relative to the center of the mask against the FZP when the FZP is at the margin of the hologram. The shifting of the mask will result in only a phase shift and will not change the intensity distribution of the reconstructed point. Thus, by using the MS method, aliasing and vignetting are simultaneously alleviated in any combination of object size and object distance.

10.
J Opt Soc Am A Opt Image Sci Vis ; 29(9): 1956-64, 2012 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-23201953

RESUMO

The well-sampling conditions for the digital calculations of the scalar diffraction, including the Huygens convolution method (HCM), the angular spectrum method (ASM), and the Fresnel diffraction integral (FDI), were discussed. We found the aliasing always occurs unless proper zero-padding--that is, to pad zero-value pixels around the initial field--is applied prior to the simulation of the diffraction. From the aspect of well-sampling, the ASM is applicable to a short propagation distance, while the HCM is applicable to a long propagation distance. However, we found that the free-space point spread function in the HCM is low-pass filtered when the propagation distance is long. As a result, it is recommended to always use the ASM in conjunction with sufficient zero-padding for the digital calculation of the diffraction field. The FDI can be directly applied to a long-distance propagation without the necessity of the zero-padding, provided only the intensity is of interest. If the phase of the diffraction field is important, the zero-padding is necessary and the propagation distance is severely restricted.

11.
Opt Lett ; 37(13): 2574-6, 2012 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-22743459

RESUMO

Optical scanning holography (OSH) is a promising technique to acquire a big-size digital hologram. However, the acquisition speed is limited by the mechanical scanner. In this Letter we apply the OSH in conjunction with an anisotropic low-pass filtering pupil to acquire vertical-bandwidth-limited (VBL) holograms. The size and the acquisition time of the VBL hologram can be reduced by one order of magnitude while the horizontal resolution remains the same as the conventional scanning hologram. The VBL hologram can be coded as an off-axis hologram without any postfiltering. Meanwhile, the full horizontal bandwidth of the displaying device can be capitalized.

12.
Appl Opt ; 50(34): H128-35, 2011 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-22192997

RESUMO

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.

13.
Appl Opt ; 50(16): 2443-50, 2011 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-21629325

RESUMO

In standard (four-exposure) quadrature phase-shifting holography (QPSH), two holograms and two intensity maps are acquired for zero-order-free and twin-image-free reconstruction. The measurement of the intensity map of the object light can be omitted in three-exposure QPSH. Furthermore, the measurements of the two intensity maps can be omitted in two-exposure QPSH, and the acquisition time of the overall holographic recording process is reduced. In this paper we examine the quality of the reconstructed images in two-, three-, and four-exposure QPSH, in simulations as well as in optical experiments. Various intensity ratios of the object light and the reference light are taken into account. Simulations show that two- and three-exposure QPSH can provide reconstructed images with quality comparable to that of four-exposure QPSH at a low intensity ratio. In practice the intensity ratio is limited by visibility, and thus four-exposure QPSH exhibits the best quality of the reconstructed image. The uniformity and the phase error of the reference light are also discussed. We found in most cases there is no significant difference between the reconstructed images in two- and three-exposure QPSH, and the quality of the reconstructed images is acceptable for visual applications such as the acquisition of three-dimensional scene for display or particle tracking.

14.
Appl Opt ; 50(7): B38-45, 2011 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-21364710

RESUMO

Recently, optical image coding using a circular Dammann grating (CDG) has been proposed and investigated. However, the proposed technique is intensity based and could not be used for three-dimensional (3D) image coding. In this paper, we investigate an optical image coding technique that is complex-amplitude based. The system can be used for 3D image coding. The complex-amplitude coding is provided by a circular Dammann grating through the use of a digital holographic recording technique called optical scanning holography. To decode the image, along the depth we record a series of pinhole holograms coded by the CDG. The decoded reconstruction of each depth location is extracted by the measured pinhole hologram matched to the desired depth. Computer simulations as well as experimental results are provided.

15.
Opt Express ; 19(4): 3272-83, 2011 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-21369149

RESUMO

An approach using a liquid-crystal spatial light modulator (LC-SLM) to enlarge the depth measuring range of the projected fringe profilometry is presented. This approach is especially applicable to detect dynamic objects with micro-scale sizes. Compared with a typical 2D image system, the LC-SLM provides a better performance for a 3D shape sensing system. The main advantages include (1) a much higher allowance to increase in the depth measuring range, (2) easiness to compensate perspective distortion and geometric distortion, (3) very high accuracy (in the micron-range) and (4) only one phase measurement needed for operation.

16.
J Opt Soc Am A Opt Image Sci Vis ; 28(2): 229-37, 2011 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-21293527

RESUMO

The cross talk noise-to-signal ratio (NSR) of an angle-multiplexed holographic data storage system is studied, and we propose a method to determine the optimized multiplexing spacing with which the cross talk noise can be less than the conventional method. In our method, the optimization location at the image plane can be chosen arbitrarily, so the multiplexing of asymmetrical image patterns can be optimized. In particular, we investigate the 90° scheme and the transmission scheme angle multiplexing. For the 90° scheme, a holographic medium with a higher refractive index is recommended for cross talk-limited multiplexing. For the transmission scheme, a holographic medium with a lower refractive index is recommended for angular range-limited multiplexing. In addition, for the transmission scheme, a larger angle between the object arm and the reference arm results in less cross talk noise, whereas the highest storage density is achieved at a 45° angle.

17.
Appl Opt ; 48(34): H23-30, 2009 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-19956295

RESUMO

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 100 M 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.

18.
Opt Lett ; 34(3): 250-2, 2009 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-19183621

RESUMO

Conventional methods of quadrature phase-shifting holography require two holograms and either intensity distribution of the reference wave or that of the object wave to reconstruct an original object without the zero order and the twin-image noise in an on-axis holographic recording setup. We present a technique called two-step-only quadrature phase-shifting holography in which solely two quadrature-phase holograms are required. Neither reference-wave intensity nor an object-wave intensity measurement is needed in the technique.

19.
Appl Opt ; 45(19): 4625-30, 2006 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-16799675

RESUMO

A new method to record an image through a thick dynamic phase distorting medium by using a photorefractive LiNbO3 crystal is demonstrated. The method uses only one beam of light, the object light. By making use of the photorefractive fanning effect, gratings are formed in the LiNbO3 crystal through the interference between the object light and its own fanning light. Because the time scale of the distorting fluctuation is much shorter than the writing time of the LiNbO3 crystal, the fluctuated light does not induce any fanning. Therefore only the static portion of the image is recorded in the crystal, and the intensity distribution of the image can then be reconstructed at any later time.

20.
Opt Lett ; 30(3): 305-7, 2005 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-15751893

RESUMO

We propose a new way to record images in a photorefractive LiNbO3 crystal. This method involves only a single object light without any reference light. We believe that the recording is attained by fanning holograms that result from interference between the object light and its scattered light. Although volume gratings are involved, the recorded pattern can be viewed not only with a laser light beam that is incident over a certain angular range but also with white light.

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