Phase-only stereoscopic hologram calculation based on Gerchberg–Saxton iterative algorithm

A phase-only computer-generated holography(CGH) calculation method for stereoscopic holography is proposed in this paper.The two-dimensional(2D) perspective projection views of the three-dimensional(3D) object are generated by the computer graphics rendering techniques.Based on these views,a phase-only hologram is calculated by using the Gerchberg–Saxton(GS) iterative algorithm.Comparing with the non-iterative algorithm in the conventional stereoscopic holography,the proposed method improves the holographic image quality,especially for the phase-only hologram encoded from the complex distribution.Both simulation and optical experiment results demonstrate that our proposed method can give higher quality reconstruction comparing with the traditional method.     

大景深彩虹全息图的获得与观察条件

本文从彩虹全息的线状点基元全息图入手,首次对其景深进行了分析和讨论.理论上证明了只要满足一定的观察条件,则彩虹全息可以进行大景深的记录和再现;实验上获得了景深达450mm的彩虹全息图.     

Effects of device resolution on three-dimensional integral imaging

We present the effects of a finite number of pixels in elemental images on the resolution and the depth of focus in three-dimensional integral imaging (II). We show that the number of pixels in elemental images determines not only the lateral resolution but also the depth resolution. The minimum number of pixels required in each elemental image is calculated to avoid depth-of-focus degradation. We evaluate how II system performance degrades as the number of pixels in each elemental image changes. The product of the depth of focus and the lateral resolution squared is used as the performance metric.     

Spectral resolution enhancement by chemical shift imaging

Three-dimensional chemical shift imaging (3D CSI) with appropriate data postprocessing can be used as a tool to improve spectral resolution in samples where large susceptibility differences and limited shim capabilities prevent good sample shimming. Data postprocessing is reduced to the realignment of individual 3D voxel spectra. As a result, the line broadening due to the field inhomogeneity over the sample's volume is reduced to the broadening by inhomogeneity within individual voxels. We compared this method with the resolution enhancement by window multiplication. We demonstrated, theoretically and experimentally, that in the presence of large, lower-order gradients, 3D CSI achieves better resolution enhancement with smaller sensitivity losses. An application of the method to a simple biological system is presented as well.     

Complex gamma-ray hologram: solution to twin images problem in atomic resolution imaging

A new technique for high fidelity three-dimensional imaging of atomic structure with gamma-ray holography is demonstrated. A complex hologram was constructed from holograms recorded for different values of the nuclear scattering amplitude on both sides of the (57)Fe M?ssbauer resonance. The holographic reconstruction was applied to this complex hologram resulting in a twin-image-free image of the bcc Fe local structure. The proposed procedure allows the removal of the twin images for all real space, making gamma-ray holography an unambiguous tool for atomic and magnetic structure imaging.     

基于超分辨率重建的图像增强算法研究

 为了提高图像分辨率,从软件的角度出发,对低分辨率图像序列重建高分辨率图像的原理和算法实现开展了研究,提出从多个低分辨率图像序列中获取更高分辨率图像的方法。通过采用基于光流场的金字塔分层结构实现由粗到精的图像配准,获取了亚像素的运动估计。在采用多帧低分辨率图像进行亚像素级配准后,提出采用动态自适应确定正则化参数的方法,构造了简单的正则化代价函数,建立了低分辨率图像与高分辨率图像之间关系的重建模型,仿真实验结果表明该超分辨率重建算法水平和垂直方向上分辨率各增加一倍,与其他算法相比清晰度更高,计算时间不到传统POCS算法的一半。     

One-dimensional integral imaging based on parallax barrier

One-dimensional integral imaging (1DII) which only has horizontal disparity is a practical solution of high resolution in the vertical direction, low-cost, easy-viewable three-dimensional (3D) display. A 1DII based on a parallax barrier is proposed in this paper. The 1DII consists of a parallax barrier and a display panel. The operation principle and parameter calculation of the 1DII are described in detail. Two prototypes of the proposed 1DII and conventional 1DII based on a lenticular lens array are developed. The proposed 1DII improves the quality of the 3D image and provides larger viewing angle than that based on a lenticular lens array, and it is simpler and has lower cost than that based on a lenticular lens array.     

Improved depth extraction method of 3D objects using computational integral imaging reconstruction based on multiple windowing techniques

This paper presents an improved depth extraction method of 3D objects using computational integral imaging reconstruction (CIIR) based on the multiple windowing models. The proposed method records 3D objects using the lenslet array; and it reconstructs multiple sets of slice images from multiple CIIR methods based on the different windowing models. A depth map is then extracted by a block matching algorithm among multiple set of slice images. A preliminary experiment is carried out to show the feasibility of the proposed method. Experimental results indicate the proposed method outperforms the previous method with two windowing models.     

An enhanced method for generation of binary Fresnel hologram based on adaptive and uniform grid-cross down-sampling

It has been revealed in past research that by uniformly down-sampling the object image prior to the numerical generation, and subsequent binarization of its digital Fresnel hologram, the reconstructed image can preserve the shaded content with favorable visual quality. However, the down-sampling process also severs the lines and blurs the edge patterns that are important in representing the detail information of an image scene. In this paper, we propose a method to overcome this dilemma with an integration of a fast adaptive down-sampling and the uniform down-sampling process. Experimental evaluation has demonstrated that our method is capable of preserving lines and edges, as well as the shaded regions, resulting in superior visual quality of the reconstructed image as compared with the existing approach. In addition, the computation time on the integrated down-sampling method is less than 200 ms on a typical personal computer.     

Depth-enhanced three-dimensional-two-dimensional convertible display based on modified integral imaging

A depth-enhanced three-dimensional-two-dimensional convertible display that uses a polymer-dispersed liquid crystal based on the principle of integral imaging is proposed. In the proposed method, a lens array is located behind a transmission-type display panel to form an array of point-light sources, and a polymer-dispersed liquid crystal is electrically controlled to pass or to scatter light coming from these point-light sources. Therefore, three-dimensional-two-dimensional conversion is accomplished electrically without any mechanical movement. Moreover, the nonimaging structure of the proposed method increases the expressible depth range considerably. We explain the method of operation and present experimental results.     

Artifact analysis and image enhancement in three-dimensional computational integral imaging using smooth windowing technique

We propose an artifact analysis in computational integral imaging and the image enhancement method based on the analysis using the smooth windowing technique. Blurring and lenslet artifacts, which are major problems in computational integral imaging, are defined and analyzed using a signal model. Applying a smooth and continuous window such as the triangular window to computational integral imaging reconstruction provides a dramatic improvement in terms of image quality. Experimental results are presented to show the validity of our method. To our best knowledge, this is the first trial to control a window function in computational integral imaging.     

Analysis of the depth resolution limit of luminescence diffuse optical imaging

We introduce a methodology to determine quantitatively the depth resolution limit in luminescence diffuse optical imaging. The approach is based on a Cramer-Rao statistical analysis, a noise model, and calculations of photon transport in tissues. We illustrate the method in the case of luminescence imaging in a brain-skull model, showing its potential applications in molecular imaging on small animals.     

Phase-only filtering based on sliced orthogonal nonlinear generalized decomposition

The sliced orthogonal nonlinear generalized (SONG) decomposition and correlation have been demonstrated to be powerful tools in digital image processing and promising for nonlinear optical information processing. In this paper, we propose an optical phase-only filtering system based on SONG decomposition (PBS), in which the phase-only filtering of the target and the input scene binary slices are performed separately by pairs and then added together. We numerically show that the PBS has extremely high and sharp output correlation peak compared with other optical correlators. Furthermore, such a SONG decomposition based phase-only filtering naturally inherits the nature of SONG decomposition, which has strong robustness to additive Gaussian noise and substitutive noise, and also the high light efficiency of phase-only filtering. We demonstrate that the PBS may serve as an optimized optical correlation scheme, which is promising in nonlinear optical pattern recognition.     

High resolution high field rodent cardiac imaging with flow enhancement suppression

A method that incorporates cardiorespiratory-gated 2DFT spin-echo imaging with blood flow enhancement suppression is described which enables high resolution microimaging of the rodent heart. This methodology was applied to obtain in vivo cardiac mouse and rat images with in-plane resolutions of 100–200 μm using high field vertical bore magnet systems. Suppression of intraventricular blood flow enhancement was achieved using a combined spin-echo/gradient-refocussed sequence to dephase magnetization from flowing spins prior to imaging.     

Improved viewing resolution of three-dimensional integral imaging by use of nonstationary micro-optics

We propose the use of synchronously moving micro-optics (lenslet arrays) for image pickup and display in three-dimensional integral imaging to overcome the upper resolution limit imposed by the Nyquist sampling theorem. With the proposed technique, we show experimentally that the viewing resolution can be improved without reducing the three-dimensional viewing aspect of the reconstructed image.     

Crosstalk-free integral imaging display based on double plano-convex micro-lens array

A crosstalk-free integral imaging display consisting of a display panel and double plano-convex micro-lens array is proposed.The double plano-convex micro-lens array includes two micro-lens arrays,A and B.Micro-lens array A is used to eliminate crosstalk by completely reflecting crosstalk lights.Micro-lens array B,located near micro-lens array A,is used to display three-dimensional images.Computer simulations based on ray-tracing are conducted.Crosstalk-free reconstruction images may be clearly observed from the simulation results.     

基于光照-反射成像模型和形态学操作的多谱段图像增强算法

为解决多谱段降质图像增强问题,提出了一种基于光照-反射成像模型和形态学操作的多谱段图像增强算法.首先对图像饱和度使用自适应非线性拉伸函数进行拉伸,使增强后的图像色彩更加饱和、自然;接下来利用引导滤波算法提取出图像的光照分量,提出了一种基于细节特征的加权融合策略,利用光照分布特性构造了一种自适应Gamma校正函数对光照分量进行处理,并将其与利用对比度受限的自适应直方图均衡化方法处理后的光照分量以及原始光照分量进行融合;然后在反射分量校正时,构造了一种形态学操作函数来校正反射信息;最后合并光照分量和反射分量,并与处理后的饱和度分量和色调分量一起得到增强图像.采用主客观评价指标对可见光低照度图像、水下图像、高动态范围图像、沙尘暴图像、雾天图像和热红外图像6种降质多谱段图像实验结果进行分析比较,结果表明本文算法能够有效地抑制图像噪声、增强图像细节信息、改善图像视觉效果,可应用于多种图像增强领域.     

Temporal contrast enhancement of picosecond pulses based on phase-conjugate wave generation

A practical technique based on the phase-conjugate wave (PCW) generation is proposed to improve the temporal contrast of the picosecond pulses. Our theory predicts the temporal contrast of the picosecond pulses can be enhanced to about the cube of the temporal contrast of the input pulse via the PCW generation, in which the conversion efficiency from the incident pulse to the PCW is about 25%. In a proof-of-principle experiment, the temporal contrast of picosecond pulses was enhanced from 1.7×10³ to 8.6×10⁸ with the conversion efficiency of 10%. This technique is promising to effectively eliminate the background of the ultrashort and ultraintense laser pulses in the future.