Improvement of image quality of digital holographic reconstruction and development of related systems

The introduction of speckle noise in the process of digital holographic reconstruction is inevitable. Meanwhile, the quality of the reconstructed images are seriously lower than that of the original images, affecting the visual perception. The removal of speckle noise is an internationally recognized conundrum. Currently, scholars have not proposed a better method to remove speckle noise, which hinders the further development of digital holography technology. As a result, reducing speck noise in digital holographic reconstruction and enhancing the quality of reconstructed images have become important research topics. Based on the characteristics of speckle noise in reconstructed images, this paper proposes a new method for the first time by combining the concepts of image segmentation, guided filtering, and filter reconstruction, which can significantly improve the image quality within a reasonable time. By comparison with other state-of-the-art methods, the proposed method perform excellently in terms of detail preservation and background noise suppression of the target image. Finally, a holographic reconstruction image quality enhancement system is developed, integrating the physical experiment of digital holographic reconstruction with the image quality enhancement algorithm. The simple and convenient operation of the system provides great help for non-algorithm physics researchers. Additionally, it is also the first holographic reconstruction image enhancement system with a good effect and has considerable market application value.

     

菲涅耳全息图的CCD记录及重现

为了更好地进行菲涅耳全息图的CCD记录及重现,设计了一种CCD同轴全息图的重构算法,该方法首先用CCD代替传统干版直接记录菲涅耳同轴全息图,并以位图形式存储到计算机中;然后利用数值计算代替光学衍射过程来再现物体的像;最后通过实验验证了该算法及数字全息图的不可撕毁性。     

分数傅里叶变换的快速算法及计算全息图的研究

通过分析菲涅耳衍射积分的快速算法,依据Lohmann提出的任意阶的分数傅里叶变换的单透镜光学实验装置,详细分析了光场在此单透镜系统中的传播过程,提出了一种基于傅里叶变换的分数傅里叶变换快速算法,并对基于此快速算法的分数傅里叶变换全息图的计算机生成与数字重现进行了研究。实验结果示出了分数傅里叶变换全息图及其在重构过程中分数阶匹配与否的实验结果,验证了分数傅里叶变换分数阶的重要性质和笔者提出算法的可行性。     

CCD直接记录菲涅耳全息图和计算机模拟实现数字重现

用CCD代替传统干版直接记录菲涅耳同轴全息图,以位图形式存储到计算机中,利用数值计算代替光学衍射过程再现物体的像.完成CCD同轴全息纪录的实验设计和数字重构的算法,并用计算机程序对数字全息图的特性进行了验证.     

分数傅立叶变换计算全息图的算法研究

传统的计算机产生全息图方法由于在标量衍射的光场描述中没有一个统一的数值计算方法,从而计算复杂度高而且重构的3D图像的体积和视场都比较小,离市场化的要求距离远.因此,在目前的计算机硬件条件下,算法和显示系统的研究仍有很大的空间.将分数傅里叶变换引入到全息图的计算中,提出一种分数傅立叶变换产生计算全息图的方法.实验结果表明,分数傅里叶变换相对于传统的傅里叶变换在记录全息数据方面的优越性,并用计算机模拟效果表明了算法的优越性.     

分数傅里叶全息图的快速算法及数字重现

论文通过分析菲涅耳衍射积分的快速算法,提出了一种基于快速傅里叶变换的分数傅里叶变换的数值模拟算法,并研究了基于此快速算法的分数傅里叶变换全息图的计算机生成及数字重现。     

Visual perception of noise in a simulated holographic display—A user study

This work explores ways to bypass the fundamental image quality limitations of displays using Computer Generated Holograms (CGHs) and, specifically, the high-frequency noise associated with phase-only holograms. Although there is a wealth of literature on building experimental holographic systems, there are no user studies to assess the performance of a holographic system projecting a dynamic two-dimensional image. In this study, 18 participants blindly compared three groups of images displayed on a conventional monitor. The first group contained the original image, the second the simulated holographic reconstruction of the original image, and the third group had the foveated reconstruction of the original image, based on the pupil position. Holograms in the second group were computed using the Fienup algorithm and the third group using the Fienup with Perceptual Don’t Care Areas (FiPDoC) algorithm, a novel algorithm that uses eye tracking to optimize image quality in CGHs. The aim of the study was to find out if the holographic display, assuming an ideal hardware, can be as good as a conventional display and whether eye tracking can help this goal. Most participants distinguished between the original image and the un-foveated simulated reconstruction. However, the participants could not differentiate between the original image and the foveated reconstruction. Thus, foveation may be essential in designing and building the first commercial holographic displays.     

基元全息图的计算机模拟及数字重现

对基元全息图进行了理论分析,给出了在菲涅耳近似条件下重现像的位置坐标和物光光源、参考光源及重现光源位置坐标之间的关系,并进行了计算机模拟和数字重现,结果与理论完全符合,为光学全息提供了可视化的验证。     

Super-resolution image reconstruction for mobile devices

With advanced mobile devices, the mobile applications of the high-definition display attract a lot of attentions nowadays. The existing image super-resolution methods are computationally inefficient for the high-definition display on the mobile devices. In this paper, we point out that the above critical issue deteriorates the display quality of the high-definition mobile devices. We propose an efficient and effective algorithm to reconstruct the high-resolution images for the mobile devices. Our algorithm outperforms previous approaches in not only smaller running time but also the higher quality of the super-resolution image reconstruction for the mobile devices.     

彩色全息压缩重构

压缩全息搭起Gabor全息和压缩感知(Compressed sensing, CS)理论之间的桥梁, 特别适合从单帧二维全息测量数据中重建三维对象, 是一种新兴的三维重建技术. 本文将压缩全息方法从单波长情形推广到多波长, 提出一种基于三维总变分稀疏模型的改进彩色全息压缩成像方法, 建立多波长情形下的压缩测量模型. 该方法利用对象的稀疏先验知识, 从单帧二维彩色全息图中重建多波长三维对象, 有效地实现孪生像的抑制和多层切片相互之间的散焦图像对重建质量的影响. 数值实验结果验证了本文提出方法的有效性.     

Viewfinder Alignment

The viewfinder of a digital camera has traditionally been used for one purpose: to display to the user a preview of what is seen through the camera's lens. High quality cameras are now available on devices such as mobile phones and PDAs, which provide a platform where the camera is a programmable device, enabling applications such as online computational photography, computer vision‐based interactive gaming, and augmented reality. For such online applications, the camera viewfinder provides the user's main interaction with the environment. In this paper, we describe an algorithm for aligning successive viewfinder frames. First, an estimate of inter‐frame translation is computed by aligning integral projections of edges in two images. The estimate is then refined to compute a full 2D similarity transformation by aligning point features. Our algorithm is robust to noise, never requires storing more than one viewfinder frame in memory, and runs at 30 frames per second on standard smartphone hardware. We use viewfinder alignment for panorama capture, low‐light photography, and a camera‐based game controller.     

全息显示中的数码光栅的计算

在基于计算机的全息(CGH)显示中,数码光栅的计算方法是关键问题,传统的模拟光学全息的计算不仅复杂而且数据量大,不易实现。文章从全息成像角度出发,介绍了二维及三维数码光栅的计算方法,包括模拟退火算法、迭代算法,实现了物理上可用的全息条纹模式,给出了计算机模拟结果,实验证明,该算法应用在数码光栅的计算上具有明显的优势和较强的鲁棒性。     

A framework for holographic scene representation and image synthesis

We present a framework for the holographic representation and display of graphics objects. As opposed to traditional graphics representations, our approach reconstructs the light wave reflected or emitted by the original object directly from the underlying digital hologram. Our novel holographic graphics pipeline consists of several stages including the digital recording of a full-parallax hologram, the reconstruction and propagation of its wavefront, and rendering of the final image onto conventional, framebuffer-based displays. The required view-dependent depth image is computed from the phase information inherently represented in the complex-valued wavefront. Our model also comprises a correct physical modeling of the camera taking into account optical elements, such as lens and aperture. It thus allows for a variety of effects including depth of field, diffraction, interference, and features built-in anti-aliasing. A central feature of our framework is its seamless integration into conventional rendering and display technology which enables us to elegantly combine traditional 3D object or scene representations with holograms. The presented work includes the theoretical foundations and allows for high quality rendering of objects consisting of large numbers of elementary waves while keeping the hologram at a reasonable size     

Optimization of digital holographic setup by a fuzzy logic prediction system

In this study, the optimization of the digital holography setup is achieved by a using fuzzy logic prediction system. In fact, when this optimization process is experimentally performed, some parameters are changed in the setup. These parameters affect directly the obtained image quality after a reconstruction process, which is determined by normalized root mean square. The aim of this study is to achieve the optimization of digital holographic setup by using both experimental and fuzzy logic prediction systems. Furthermore, the required time during the experimental optimization can be lowered by using a numerical method like the fuzzy logic prediction system. Here, the experimental optimization results and the optimization results obtained by the fuzzy logic prediction system are compared. It is offered that the designed experimental system can be optimized by using an artificial intelligent tool. The applied fuzzy logic prediction model is used the first time for optimization of hologram recording setup. As a result, it is reached a conclusion that the optimization of digital holographic setup can be numerically performed by the fuzzy logic prediction system. Moreover, while digital holographic setup is experimentally designed, the required time for optimization is reduced, as well.     

Fast optimization of computer-generated holograms using conjugate gradient

Holographic display, as an ideal three-dimensional (3D) display method, can provide a realistic stereo-perception sense, and is expected to be used in the next generation of augmented reality (AR) prototypes without complex optical devices. While holographic 3D displays have been proposed in the past decades, high-quality holographic reconstructed images have always relied on well-designed generation algorithms, and it is still a challenge to obtain an accurate phase profile fast. In this work, we utilize a first-order optimization algorithm to optimize the phase profile using the conjugate gradient direction instead of the steepest gradient direction to update the phase parameters. We validate this proposed method by comparing the current widely used stochastic gradient method and the wirtinger holography method. The simulation and experimental results illustrate the superiority of the proposed method, which can achieve faster optimization with the same quality metrics.     

基于干涉法的计算全息图的生成

三维技术已经越来越广泛地应用于计算机图像学中。近年来,全息又成为制作高质量3D图像最为普遍的方法。文中主要讲述了光全息的有关知识,并讨论了基于干涉全息图的计算方法。以点光源的计算全息方法为例,利用计算机模拟光干涉,并计算出各点光的相位,生成了基于干涉的点光源的全息图。     

分数傅里叶变换合成计算全息与数字重现

传统的计算全息图大多采用菲涅耳衍射积分得到,但菲涅耳衍射积分在描述整个衍射光场中,没有一个统一的采样方法对积分进行数值计算,从而给计算带来不便。为了更好地研究计算全息图问题,文章引入了分数傅里叶变换,通过利用分数傅里叶变换的一种快速数值模拟算法,提出了一种基于分数傅里叶变换的合成空间三维物体全息图的新方法,并用计算机模拟了合成的全息图及其数字重构的结果。实验结果表明:由于分数阶的引入,得到一种处理光场衍射问题的统一算法,因此用分数傅里叶变换来处理光场衍射问题是十分理想的。     

分数傅立叶全息图的算法研究及系统实现

将分数傅里叶变换引入到全息图的计算中,提出一种分数傅立叶变换产生计算全息图的方法,并利用拆卸的投影装置搭建出以空间光调制器DMD为核心的全息显示光学系统并获得了分数傅里叶变换计算全息图在该系统下的全息显示效果及计算机模拟效果。     

Numerical investigation of zoomable holographic projection without a zoom lens

Holographic projection is for laser displays and has the merits of being aberration free, producing high‐contrast images, having the ability of color reconstruction with one spatial light modulator, and so on. In this paper, we propose a zoomable holographic projection without using a zoom lens and verify the proposed method by using numerical simulation. Although such a system can be readily realized to use the features of holography, which is capable of recording a large image exceeding the hologram size, the required calculation is very time consuming. For acceleration, we used shifted Fresnel diffraction for setting different sampling rates on a hologram and projected image. The proposed method can project any zoom‐in and zoom‐out image between zeroth‐order and first‐order lights, and the processing time and required memory for the zoom are constant.     

基于非局部相似模型的压缩感知图像恢复算法

针对压缩感知(Compressed sensing, CS)图像恢复问题, 提出了一种基于非局部相似模型的压缩感知恢复算法, 该算法将传统意义上二维图像块的稀疏性扩展到相似图像块组在三维空间上的稀疏性, 在提高图像表示稀疏度的同时进一步提高了压缩感知图像恢复效率, 恢复图像在纹理和结构保持方面都得到了很大的提升. 在该算法模型求解过程中, 使用增广拉格朗日方法将受限优化问题转换为非受限优化问题, 为减少计算复杂度, 还使用了基于泰勒展开的线性化技术来加速算法求解. 实验结果表明, 该算法的图像恢复性能优于目前主流的压缩感知图像恢复算法.