Hologram classification of occluded and deformable objects with speckle noise contamination by deep learning.

Advancements in optical, computing, and electronic technologies have enabled holograms of physical three-dimensional (3D) objects to be captured. The hologram can be displayed with a spatial light modulator to reconstruct a visible image. Although holography is an ideal solution for recording 3D images, a hologram comprises high-frequency fringe patterns that are almost impossible to recognize with traditional computer vision methods. Recently, it has been shown that holograms can be classified with deep learning based on convolution neural networks. However, the method can only achieve a high success classification rate if the image represented in the hologram is without speckle noise and occlusion. Minor occlusion of the image generally leads to a substantial drop in the success rate. This paper proposes a method known as ensemble deep-learning invariant occluded hologram classification to overcome this problem. The proposed new method attains over 95% accuracy in the classification of holograms of partially occluded handwritten numbers contaminated with speckle noise. To achieve the performance, a new augmentation scheme and a new enhanced ensemble structure are necessary. The new augmentation process includes occluded objects and simulates the worst-case scenario of speckle noise.

Optimal sampled phase-only hologram (OSPOH).

A sampled phase-only hologram (SPOH) is the phase component of the hologram of an object image with pixels being sampled with a periodic grid-cross pattern. The reconstructed image of a SPOH is a sparse image with abundant empty voids and degradation in sharpness and contrast. In this paper we proposed a method based on a new sampling scheme, together with stochastic binary search (SBS), to obtain an optimal sampling lattice that can be applied to generate phase-only holograms with enhanced reconstructed image. Experimental results show that with our proposed method, the fidelity and quality of the reconstructed image are increased.

Ensemble convolutional neural network for classifying holograms of deformable objects.

Recently, a method known as "ensemble deep learning invariant hologram classification" (EDL-IHC) for classifying of holograms of deformable objects with deep learning network (DLN) has been demonstrated. However DL-IHC requires substantial computational resources to attain near perfect success rate (≥99%). In practice, it is always desirable to have higher success rate with a low complexity DLN. In this paper we propose a low complexity DLN known as "ensemble deep learning invariant hologram classification" (EDL-IHC). In comparison with DL-IHC, our proposed hologram classifier has promoted the success rate by 2.86% in the classification of holograms of handwritten numerals.

Phase sensitivity of off-axis digital holography.

In off-axis digital holography, the Fourier transform-based algorithm is commonly used for signal processing. Here, we derive the theoretical phase sensitivity of this algorithm, which can be calculated from a single 2D hologram. This algorithm sensitivity represents the best achievable sensitivity of a system using this algorithm. Our derivation treats the signal in its most general form, considering non-uniform illumination and the effect of sideband filtering. As a result, phase sensitivity varies spatially, determined by local signal-to-noise ratio. Sensitivity expressions for both shot noise and uniform noise models are given. These results are validated with simulations and experiments. Significantly, this theoretical sensitivity can serve as a baseline metric for assessing performance of a phase-imaging system, such as experimental sensitivity and hardware stability, which are critical for high-sensitivity quantitative phase imaging. In addition, the results are equally applicable to other interferometric techniques with similar interferogram patterns and signal processing algorithms.

Acousto-Optics 2017: introduction to the feature issue.

The editors of Acousto-Optics 2018 provide an overview of the featured papers in the context of the 13th School of Acousto-Optics and Applications from which the articles were drawn.

Generation of patterned-phase-only holograms (PPOHs).

A fast and non-iterative method for generating a phase-only hologram, hereafter referred to as the patterned-phase-only hologram (PPOH), is reported in this paper. Briefly, a phase mask with a periodic phase pattern is added to the source image, and converted into a hologram. Subsequently, only the phase component is retained as a phase-only hologram. Experimental evaluation reveals that the visual quality of the reconstructed images of the PPOH generated with our proposed method is favorable, and superior to that obtained with existing methods.

Generation of complementary sampled phase-only holograms.

If an image is uniformly down-sampled into a sparse form and converted into a hologram, the phase component alone will be adequate to reconstruct the image. However, the appearance of the reconstructed image is degraded with numerous empty holes. In this paper, we present a low complexity and non-iterative solution to this problem. Briefly, two phase-only holograms are generated for an image, each based on a different down-sampling lattice. Subsequently, the holograms are displayed alternately at high frame rate. The reconstructed images of the 2 holograms will appear to be a single, densely sampled image with enhance visual quality.

Low Complexity Compression and Speed Enhancement for Optical Scanning Holography.

In this paper we report a low complexity compression method that is suitable for compact optical scanning holography (OSH) systems with different optical settings. Our proposed method can be divided into 2 major parts. First, an automatic decision maker is applied to select the rows of holographic pixels to be scanned. This process enhances the speed of acquiring a hologram, and also lowers the data rate. Second, each row of down-sampled pixels is converted into a one-bit representation with delta modulation (DM). Existing DM-based hologram compression techniques suffers from the disadvantage that a core parameter, commonly known as the step size, has to be determined in advance. However, the correct value of the step size for compressing each row of hologram is dependent on the dynamic range of the pixels, which could deviate significantly with the object scene, as well as OSH systems with different opical settings. We have overcome this problem by incorporating a dynamic step-size adjustment scheme. The proposed method is applied in the compression of holograms that are acquired with 2 different OSH systems, demonstrating a compression ratio of over two orders of magnitude, while preserving favorable fidelity on the reconstructed images.

Dairy and nondairy beverage consumption for childhood atopic eczema: what health advice to give?

BACKGROUND: Many parents of children with atopic eczema (AE) practise empirical dietary avoidance and supplementation, and seek healthcare advice on whether consumption of dairy and nondairy beverages may be beneficial or detrimental for this condition. AIM: We investigated if frequency of consumption of beverages was associated with disease severity and quality of life (QoL). METHODS: Parent-reported frequency of drinks and beverages were recorded in consecutive children with AE, and disease severity (Nottingham Eczema Severity Score; NESS), QoL (Children's Dermatology Life Quality Index; CDLQI), skin hydration (SH), transepidermal water loss (TEWL), blood pressure (BP), resting heart rate (RHR) and body mass index (BMI) were evaluated. RESULTS: AE was associated with worse QoL than miscellaneous non-AE skin diseases (P < 0.001). Compared with children without AE, there was a trend for children with AE to drink less milk (P = 0.06) and more miscellaneous beverages (such as Chinese herbal tea and soymilk; P = 0.03). In children with AE, NESS correlated with CDLQI (ρ = 0.66, P < 0.001) and reduced SH (ρ = -0.32, P < 0.001), whereas CDLQI correlated with a higher RHR (ρ = 0.25, P < 0.01). Multiple logistic regression showed that male sex (OR = 0.44, 95% CI 0.20-0.97; P = 0.04) and drinking fresh milk (OR = 0.42, 95% CI 0.20-0.93; P = 0.03) were independent factors associated with less severe disease. Moderate to severe impairment of CDLQI was associated with NESS (OR = 1.48, 95% CI 1.28-1.71; P < 0.001) and RHR (OR = 1.05, 95% CI 1.02-1.08; P < 0.01) but not with reported habits of beverage consumption. Concerning cardiovascular health in AE, frequency of formula milk consumption was associated with RHR (ρ = 0.17, P = 0.04), and soft drink consumption was associated with higher systolic blood pressure (SBP) (ρ = 0.18, P = 0.04). CONCLUSION: This study provides evidence for parental/patient guidance. Children with AE who reported more fresh milk consumption had less severe disease. There was no correlation between consumption of nondairy beverages with disease severity or QoL, but frequency of soft drink consumption correlated with SBP. With these results being supported by a literature review, it is reasonable to advise parents that fresh milk can be consumed by unsensitized children with AE. Soft drinks and other beverages should not be consumed in excess for optimal cardiovascular health and for other health reasons.

Fast generation of digital holograms based on warping of the wavefront recording plane.

This paper reports a fast method for generating a 2048x2048 digital Fresnel hologram at a rate of over 100 frames per second. Briefly, the object wave of an image is nonuniformally sampled and generated on a wavefront recording plane (WPR) that is close to the object scene. The sampling interval at each point on the WRP image is then modulated according to the depth map. Subsequently, the WRP image is converted into a hologram. The hologram generated with our proposed method, which is referred to as the warped WRP (WWRP) hologram, is capable of presenting a 3-D object with faster speed as compared with existing methods.

Generation of phase-only Fresnel hologram based on down-sampling.

We present a novel non-iterative method for generating phase-only Fresnel holograms. The intensity image of the source object scene is first down-sampled with uniform grid-cross lattices. A Fresnel hologram is then generated from the intensity and the depth information of the sampled object points. Subsequently, only the phase component of the hologram is preserved, resulting in a pure phase hologram that we call the sampled-phase-only hologram (SPOH). Experimental evaluation reveals that the numerical, as well as the optical reconstructed images of the proposed phase-only hologram derived with our method are of high visual quality. Moreover, the reconstructed optical image is brighter, and less affected by phase noise contamination on the hologram as compared with those generated with existing error-diffusion approaches.

Review of holographic-based three-dimensional object recognition techniques [invited].

With the advancement of computing and optical technologies, it is now possible to capture digital holograms of real-life object scenes. Theoretically, through the analysis of a hologram, the three-dimensional (3D) objects coded on the hologram can be identified. However, being different from an optical image, a hologram is composed of complicated fringes that cannot be analyzed easily with traditional computer vision methods. Over the years, numerous important research investigations have been attempted to provide viable solutions to this problem. The aim of this work is three-fold. First, we provide a quick walkthrough on the overall development of holographic-based 3D object recognition (H3DOR) in the past five decades, from film-based approaches to digital-based innovation. Second, we describe in more detail a number of selected H3DOR methods that are introduced at different timelines, starting from the late sixties and then from the seventies, where viable digital holographic-based 3D recognition methods began to emerge. Finally, we present our work on digital holographic, pose-invariant 3D object recognition that is based on a recently introduced virtual diffraction plane framework. As our method has not been reported elsewhere, we have included some experimental results to demonstrate the feasibility of the approach.

Fast conversion of digital Fresnel hologram to phase-only hologram based on localized error diffusion and redistribution.

Past research has demonstrated that a digital, complex Fresnel hologram can be converted into a phase-only hologram with the use of the bi-direction error diffusion (BERD) algorithm. However, the recursive nature error diffusion process is lengthy and increases monotonically with hologram size. In this paper, we propose a method to overcome this problem. Briefly, each row of a hologram is partitioned into short non-overlapping segments, and a localized error diffusion algorithm is applied to convert the pixels in each segment into phase only values. Subsequently, the error signal is redistributed with low-pass filtering. As the operation on each segment is independent of others, the conversion process can be conducted at high speed with the graphic processing unit. The hologram obtained with the proposed method, known as the Localized Error Diffusion and Redistribution (LERDR) hologram, is over two orders of magnitude faster than that obtained by BERD for a 2048×2048 hologram, exceeding the capability of generating quality phase-only holograms in video rate.

Novel method for converting digital Fresnel hologram to phase-only hologram based on bidirectional error diffusion.

We report a novel and fast method for converting a digital, complex Fresnel hologram into a phase-only hologram. Briefly, the pixels in the complex hologram are scanned sequentially in a row by row manner. The odd and even rows are scanned from opposite directions, constituting to a bidirectional error diffusion process. The magnitude of each visited pixel is forced to be a constant value, while preserving the exact phase value. The resulting error is diffused to the neighboring pixels that have not been visited before. The resulting novel phase-only hologram is called the bidirectional error diffusion (BERD) hologram. The reconstructed image from the BERD hologram exhibits high fidelity as compared with those obtained with the original complex hologram.

Displaying a high-resolution digital hologram on a low-resolution spatial light modulator with the same resolution obtained from the hologram.

In this paper, a fast method for displaying a digital, real and off-axis Fresnel hologram on a lower resolution device is reported. Preserving the original resolution of the hologram upon display is one of the important attributes of the proposed method. Our method can be divided into 3 stages. First, a digital hologram representing a given three dimensional (3D) object is down-sampled based on a fix, jitter down-sampling lattice. Second, the down-sampled hologram is interpolated, through pixel duplication, into a low resolution hologram that can be displayed with a low-resolution spatial light modulator (SLM). Third, the SLM is overlaid with a grating which is generated based on the same jitter down-sampling lattice that samples the hologram. The integration of the grating and the low-resolution hologram results in, to a good approximation, the resolution of the original hologram. As such, our proposed method enables digital holograms to be displayed with lower resolution SLMs, paving the way for the development of low-cost holographic video display.

Applied Optics Golden Anniversary commemorative reviews: introduction.

Applied Optics presents three special issues to end its retrospective of Applied Optics' 50 years. The special issues are interference, interferometry, and phase; imaging, optical processing, and telecommunications; and polarization and scattering. The issues, which contain 19 commemorative reviews from some of the journal's luminaries, are summarized.

Zinc-finger protein 331, a novel putative tumor suppressor, suppresses growth and invasiveness of gastric cancer.

Zinc-finger protein 331 (ZNF331), a Kruppel-associated box zinc-finger protein gene, was identified as a putative tumor suppressor in our previous study. However, the role of ZNF331 in tumorigenesis remains elusive. We aimed to clarify its epigenetic regulation and biological functions in gastric cancer. ZNF331 was silenced or downregulated in 71% (12/17) gastric cancer cell lines. A significant downregulation was also detected in paired gastric tumors compared with adjacent non-cancer tissues. In contrast, ZNF331 was readily expressed in various normal adult tissues. The downregulation of ZNF331 was closely linked to the promoter hypermethylation as evidenced by methylation-specific PCR, bisulfite genomic sequencing and reexpression by demethylation agent treatment. DNA sequencing showed no genetic mutation/deletion of ZNF331 in gastric cancer cell lines. Ectopic expression of ZNF331 in the silenced cancer cell lines MKN28 and HCT116 significantly reduced colony formation and cell viability, induced cell cycle arrests and repressed cell migration and invasive ability. Concordantly, knockdown of ZNF331 increased cell viability and colony formation ability of gastric cancer cell line MKN45. Two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomic approach were applied to analyze the molecular basis of the biological functions of ZNF331. In all, 10 downstream targets of ZNF331 were identified to be associated with regulation of cell growth and metastasis. The tumor-suppressive effect of ZNF331 is mediated at least by downregulation of genes involved in cell growth promotion (DSTN, EIF5A, GARS, DDX5, STAM, UQCRFS1 and SET) and migration/invasion (DSTN and ACTR3), and upregulation of genome-stability gene (SSBP1) and cellular senescence gene (PNPT1). A novel target of ZNF331 (DSTN) was functionally validated. Overexpression of DSTN in BGC-823 cells increased colony formation and migration ability. In conclusion, our results suggest that ZNF331 possesses important functions for the suppression of gastric carcinogenesis as a novel functional tumor-suppressor gene.

Binary mask programmable hologram.

We report, for the first time, the concept and generation of a novel Fresnel hologram called the digital binary mask programmable hologram (BMPH). A BMPH is comprised of a static, high resolution binary grating that is overlaid with a lower resolution binary mask. The reconstructed image of the BMPH can be programmed to approximate a target image (including both intensity and depth information) by configuring the pattern of the binary mask with a simple genetic algorithm (SGA). As the low resolution binary mask can be realized with less stringent display technology, our method enables the development of simple and economical holographic video display.

Enhancing the pictorial content of digital holograms at 100 frames per second.

We report a low complexity, non-iterative method for enhancing the sharpness, brightness, and contrast of the pictorial content that is recorded in a digital hologram, without the need of re-generating the latter from the original object scene. In our proposed method, the hologram is first back-projected to a 2-D virtual diffraction plane (VDP) which is located at close proximity to the original object points. Next the field distribution on the VDP, which shares similar optical properties as the object scene, is enhanced. Subsequently, the processed VDP is expanded into a full hologram. We demonstrate two types of enhancement: a modified histogram equalization to improve the brightness and contrast, and localized high-boost-filtering (LHBF) to increase the sharpness. Experiment results have demonstrated that our proposed method is capable of enhancing a 2048x2048 hologram at a rate of around 100 frames per second. To the best of our knowledge, this is the first time real-time image enhancement is considered in the context of digital holography.