Integral Imaging Method Research Articles

Wavelet Entropy-Based Method for Migration Imaging of Hidden Microcracks by Using the Optimal Wave Velocity

Exploring the shape and direction of hidden cracks in a tunnel lining structure is one of the main objectives of ground penetrating radar (GPR) map interpretation. The most important factor that restricts the migration imaging of hidden cracks is the propagation velocity of electromagnetic waves. Determining the optimal electromagnetic wave velocity is the key to truthfully restoring the actual shape of hidden cracks. To study the GPR characteristic response signals of hidden cracks, forward simulation and model experiments of different cracks were performed. Subsequently, a method to determine the optimal electromagnetic wave velocity based on the wavelet entropy theory was proposed, and the frequency wavenumber domain migration (F-K) and Kirchhoff integral migration imaging method were combined. Horizontal, S-type, and inclined hidden fractures were examined by migration imaging. The results show that the radar characteristic response images of different cracks can be simulated forward by using the finite difference time domain method to write the fracture model instruction. Based on the wavelet entropy theory, the error range between the estimated value and true value was controlled within 4%. Taking the optimal electromagnetic wave velocity as the velocity parameter of the conventional migration method can make the migration more effective and suppress the interference of echo signals so that the diffraction wave converges, and the energy is more concentrated; thus, the real fracture morphology can be restored to the greatest extent. The research results can provide technical support for the fine detection of hidden quality defects in tunnel lining structures by GPR mapping.

Large field-of-view microlens array with low crosstalk and uniform angular resolution for tabletop integral imaging display

Tabletop autostereoscopic displays have the advantage of displaying realistic three-dimensional (3D) content. In particular, the Integral imaging (InIm) method is superior in tabletop displays, as it is possible to make the system small using microlens arrays (MLA). Off-the-shelf MLAs have a small field of view (FOV) and are unsuitable for tabletop displays where the half viewing angle is typically around 45 degrees. The MLA for tabletop display also needs to have uniform angular resolution and low crosstalk to display 3D content. In this paper, we designed a new MLA with a multilayer structure and a reversed lens shape. This lens array has a wide viewing angle of −58 degrees to +58 degrees, with uniform angular resolution and low crosstalk of less than 0.2. We implemented a tabletop display using our MLA and verified its properties experimentally. The misallocation error of the elemental image is experimentally measured and compensated for as well.

Fast generation of 360-degree cylindrical photorealistic hologram using ray-optics based methods.

Due to the large pixel pitch and limited size of spatial light modulator (SLM), the field of view (FOV) of current holographic display is greatly restricted. Cylindrical holography can effectively overcome the constraints of FOV. However, the existent algorithms of cylindrical hologram are all based on the wave-optics based approach. In this paper, to the best of our knowledge, we adopt the ray-optics based approach in the generation of cylindrical computer generated hologram (CCGH) for the first time. Information of parallax images captured from three-dimensional (3D) objects using a curved camera array is recorded into a cylindrical hologram. Two different recording specific algorithms are proposed, one is based on the Fast Fourier Transform (FFT) method, and another is based on the pinhole-type integral imaging (PII) method. The simulation results confirm that our proposed methods are able to realize a fast generation of the cylindrical photorealistic hologram.

Integral lucky imaging technique for three-dimensional visualization of objects through turbulence

Integral lucky imaging method for three-dimensional visualization of objects through turbulence is presented in this work. The method picks images of objects through turbulence with better quality to get a better reconstruction. Numerical experiment was carried out to prove the effectiveness of the proposed method. Analysis as well as simulation results showed that with the decrease of turbulence inner scale, the quality of reconstruction will be reduced. The reconstruction quality can be further improved by using the mass center translation method and the region segmentation method. This paper provides a promising approach for three-dimensional imaging through turbulence.

High resolution integral imaging display by using a microstructure array

A novel integral imaging method that can be used to display three-dimensional (3D) images with high resolution is proposed. The integral imaging system consists of a delicate microstructure array and microlens array. The microstructure array displays the information of the microimage array. Due to the application of the delicate microstructure array, a large number of efficiency pixels in the microimage array are regularly imaged through the microlens array, which will result in the 3D images with high resolution. In this paper, the relationships among the resolution of the 3D images, the focal length of the microlens, microstructure array/microlens array distance, and the feature size of the microstructure array are analyzed theoretically based on optical design theories. Related experiments are performed. The microstructure array with 1 μm feature size is fabricated by the lithographic method and applied on the integral imaging system, which forms the 3D images with the resolution of 10 lines/mm. Compared with a traditional integral imaging system, the resolution of the 3D images generated by the method is effectively enhanced. It is inferred that the method has great potential for static 3D displays such as 3D photographs, 3D advertisements, and so on.

Progress of three-dimensional light-field display [Invited

In this review, the principle and the optical methods for light-field display are introduced. The light-field display is divided into three categories, including the layer-based method, projector-based method, and integral imaging method. The principle, characteristic, history, and advanced research results of each method are also reviewed. The advantages of light-field display are discussed by comparing it with other display technologies including binocular stereoscopic display, volumetric three-dimensional display, and holographic display.

Wavelet-based iterative perfect reconstruction in computational integral imaging.

We propose a new computational integral imaging (CII) method via the iterative perfect reconstruction technique to improve the visual quality of reconstructed 3D scenes. As is well known, images reconstructed by CII suffer from artifacts and, as a result, degradation of visual quality. As solutions to this problem, the regularization and iterative back-projection (IBP)-based super-resolution (SR) reconstruction algorithms have been shown to be effective for high-visual-quality reconstruction. However, computation of the regularization algorithm is very expensive, and the IBP algorithm is very sensitive to noise in the deblurring process. To address these challenges, we propose an iterative perfect reconstruction algorithm that addresses the issues of low visual quality and noise sensitivity. Experimental results indicate that our proposed method outperforms the conventional SR reconstruction-based CII methods.

Three-dimensional image authentication scheme using sparse phase information in double random phase encoded integral imaging

In recent years, many studies have focused on authentication of two-dimensional (2D) images using double random phase encryption techniques. However, there has been little research on three-dimensional (3D) imaging systems, such as integral imaging, for 3D image authentication. We propose a 3D image authentication scheme based on a double random phase integral imaging method. All of the 2D elemental images captured through integral imaging are encrypted with a double random phase encoding algorithm and only partial phase information is reserved. All the amplitude and other miscellaneous phase information in the encrypted elemental images is discarded. Nevertheless, we demonstrate that 3D images from integral imaging can be authenticated at different depths using a nonlinear correlation method. The proposed 3D image authentication algorithm can provide enhanced information security because the decrypted 2D elemental images from the sparse phase cannot be easily observed by the naked eye. Additionally, using sparse phase images without any amplitude information can greatly reduce data storage costs and aid in image compression and data transmission.

High-efficient computer-generated integral imaging based on the backward ray-tracing technique and optical reconstruction.

A high-efficient computer-generated integral imaging (CGII) method is presented based on the backward ray-tracing technique. In traditional CGII methods, the total rendering time is long, because a large number of cameras are established in the virtual world. The ray origin and the ray direction for every pixel in elemental image array are calculated with the backward ray-tracing technique, and the total rendering time can be noticeably reduced. The method is suitable to create high quality integral image without the pseudoscopic problem. Real time and non-real time CGII rendering images and optical reconstruction are demonstrated, and the effectiveness is verified with different types of 3D object models. Real time optical reconstruction with 90 × 90 viewpoints and the frame rate above 40 fps for the CGII 3D display are realized without the pseudoscopic problem.

Improved resolution integral imaging using random aperture coding based on compressive sensing

The low-resolution of the three-dimensional (3D) image is the main limitation for the development of integral imaging. We proposed a resolution enhanced integral imaging method by using a randomly coded aperture based on compressive sensing (CS). The compressive integral imaging model is derived based on wave optics theory. Instead of sensing raw pixel data, the recording device measures the compressive samples of the observed 3D scene through a random phase mask attached to each lenslet. The coded elemental images are captured with a single exposure and the super-resolution elemental images can be reconstructed by an optimization algorithm. In this paper, we use CS in the acquisition of the elemental images, and ultimately on improving the image quality of reproduced 3D scene either by optical experiment or computational method. Both the theoretical model and experimental results show the feasibility of the proposed method.

See-through multi-projection three-dimensional display using transparent anisotropic diffuser.

We propose a see-through multi-projection three-dimensional (3D) display using a transparent anisotropic diffuser. By immersing a metal-coated anisotropic diffuser into index matching oil which has the same refractive index of anisotropic diffuser, a transparent anisotropic diffuser is implemented. The reflectance of the transparent anisotropic diffuser is analyzed with the transfer matrix. Two multi-projection methods are proposed based on reflection type integral imaging and multi-view method. Especially, the reflection type multi-view-based system is realized with a curved anisotropic diffuser. High resolution see-through 3D display can be realized with the proposed methods. They can be used in various applications with the two multi-projection methods. In order to show the augmented reality features, real objects and virtual 3D images are presented at the same time in the experimental setup.

Color Artifact-Free Three-Dimensional Integral Imaging Display with Large Depth Using a Lens Array Based on Sublens Structure

Typical depth priority integral imaging (DPII) method with large depth is composed of a lens array and a display panel where the unwanted color artifact of the reconstructed 3D image may be produced due to the subpixel structure of the display panel. In this paper, to reduce color artifact in the DPII system, we propose a new DPII system with a lens array based on three sublens configurations. In the proposed system, each voxel color of 3D object is reconstructed by the integration of the subpixel images from three sublenses to display red, green, and blue colors. In addition, we introduce a new subpixel rearrangement algorithm to generate the modified elemental images for the proposed system. To show the feasibility of the proposed method, we carry out the preliminary experiments for color images and present the experimental results. The results reveal that the proposed system can reduce color artifact of 3D images compared with the conventional integral imaging system.

Real-mode depth-fused display with viewer tracking.

A real-mode depth-fused display is proposed by employing an integral imaging method in the depth-fused display system with viewer tracking. By giving depth-fusing effect between a transparent display and a floated planar two-dimensional image generated by the real-mode integral imaging method, a three-dimensional image is generated in front of the display plane unlike conventional depth-fused displays. The viewing angle of the system is expanded with a viewer tracking method. In addition, dynamic vertical and horizontal motion parallax can be given according to the tracked position of the viewer. As the depth-fusing effect is not dependent on the viewing distance, accommodation cue and motion parallax are provided for a wide range of viewing position. We demonstrate the feasibility of our proposed method by experimental system.

Reconstruction Improvement in Integral Fourier Holography by Micro-Scanning Method

Although integral holography has many promising advantages in the field of 3D imaging, the resolution of reconstructed holographic image is still limited by the insufficient information captured. To improve the reconstruction quality, an integral Fourier holographic imaging method based on micro-scanning of the micro-lens array is proposed in this paper. The micro-scanning of the micro-lens array can increase the sampling rate in spatial frequency domain and the information of the generated Fourier hologram, which will eventually eliminate the overlapping effect in the reconstructed 3D image. Experiments for different micro-scanning modes are carried out to verify the feasibility of the proposed method and to show that the reconstruction quality is effectively enhanced.

P‐80: Multiple Orthographic Image Interleaving for Generating Tilted Elemental Image Array with an Arbitrary Angle Directly

In this paper, we propose a computer‐generated integral imaging (CGII) method called multiple orthographic image interleaving (MOII) that used directly for generating tilted elemental image array (EIA) with an arbitrary angle. An orthographic view image array is obtained by rendering a three‐dimensional (3D) scene at certain positions inside a circle. After that, a pixel mapping algorithm is used to interleave the rendering results to form the tilted EIA with an arbitrary angle. The feasibility and efficiency of the proposed method are verified and analyzed through experiments. The experiment results show that the reconstructed 3D images have clear edge and have no distortion.

Multiple Orthographic Frustum Combing for Real-Time Computer-Generated Integral Imaging System

In this paper, we propose a computer-generated integral imaging (CGII) method called multiple orthographic frustum combining (MOFC), in which an elemental image array (EIA) can be generated by rendering a 3-D scene with one-shot orthographic projection using combing multiple orthographic frustum. The proposed MOFC method exploits the programmability of graphic processing unit to improve the computational efficiency. The experimental results show that the proposed method can achieve real-time computational speed for generating ultra high-definition (3840 ×2160) EIA.

P‐46: Real‐time Computer‐Generated Integral Imaging System Based on Multiple Orthographic Frustum Combining

AbstractIn this paper, we propose a computer‐generated integral imaging (CGII) method called multiple orthographic frustum combining (MOFC), in which an elemental image array (EIA) can be generated by rendering a 3D scene with one‐shot orthographic projection using combing multiple orthographic frustum. To our best knowledge, the proposed system outperforms the existing real‐time CGII system in both the speed performance and the resolution of the EIA. Experimental results show that the proposed method can achieve real‐time computational speed for generating ultra high‐definition (3840times2160) EIA.

3차원 집적 영상을 위한 우선순위 전송 기법

In this paper, we consider a representative integral imaging method in glasses-free 3D image processing and propose a prioritized transmission scheme for guaranteeing a received video quality in error-prone environments. According to the correlation of pixels consisting of each voxel of integral image, we set the priority differently and apply the modulation level according to this priority value. That is to say, the corresponding pixels with small variance are set to a high priority and transmitted by using a low level modulation that is robust under transmission errors, but the corresponding pixels with greater variance are set to a lower priority and transmitted by using a high level modulation that has a high bit error rate but fast transmission rate. Result shows that the proposed scheme that applies the error-robust modulation level to the important image bit stream with the high priority improves the peak to sidelobe ratio (PSR) of the received 3D image, compared with a typical method that use the same modulation level without distinction of priorities. 논문 14-39C-05-06 The Journal of Korea Information and Communications Society '14-05 Vol.39C No.05 http://dx.doi.org/10.7840/kics.2014.39C.5.447 447 ※ 이 논문은 2013년도 정부(교육과학기술부)의 재원으로 한국연구재단의 기초연구사업 지원을 받아 수행된 것임(2011-0025424) First Author : Hankyong National University, Department of Electrical, Electronic and Control Engineering, and the Institute for Information Technology Convergence, mjcho@hknu.ac.kr, 정회원 ° Corresponding Author : Hankyong National University, Department of Electrical, Electronic and Control Engineering, and the Institute for Information Technology Convergence, hhchoi@hknu.ac.kr, 정회원 논문번호:KICS2014-03-086, Received March 14, 2014; Revised May 7, 2014; Accepted May 7, 2014 The Journal of Korea Information and Communications Society '14-05 Vol.39C No.05

A 3D integral imaging optical see-through head-mounted display.

An optical see-through head-mounted display (OST-HMD), which enables optical superposition of digital information onto the direct view of the physical world and maintains see-through vision to the real world, is a vital component in an augmented reality (AR) system. A key limitation of the state-of-the-art OST-HMD technology is the well-known accommodation-convergence mismatch problem caused by the fact that the image source in most of the existing AR displays is a 2D flat surface located at a fixed distance from the eye. In this paper, we present an innovative approach to OST-HMD designs by combining the recent advancement of freeform optical technology and microscopic integral imaging (micro-InI) method. A micro-InI unit creates a 3D image source for HMD viewing optics, instead of a typical 2D display surface, by reconstructing a miniature 3D scene from a large number of perspective images of the scene. By taking advantage of the emerging freeform optical technology, our approach will result in compact, lightweight, goggle-style AR display that is potentially less vulnerable to the accommodation-convergence discrepancy problem and visual fatigue. A proof-of-concept prototype system is demonstrated, which offers a goggle-like compact form factor, non-obstructive see-through field of view, and true 3D virtual display.

Depth-fused display with improved viewing characteristics

We propose a depth-fused display (DFD) with enhanced viewing characteristics by hybridizing the depth-fusing technology with another three-dimensional display method such as multi-view or integral imaging method. With hybridization, the viewing angle and expressible depth range can be extended without changing the size of the volume of the system compared to the conventional DFD method. The proposed method is demonstrated with experimental system.