Design of autostereoscopic two‐view 3D that uses the spherical concave surface and the parallax barrier

Autostereoscopic display where circular concave display was used was investigated in case of the parallax barrier and two‐view 3D. Equation of the barrier pitch of the parallax barrier was derived that depended on the radius of the curved display. Trajectories of the rays coming from the curved display through the parallax barrier were calculated. Calculated distribution of ray trajectories for the autostereoscopic display using curved display showed trends similar to those for the flat display.     

A toroidal‐lens designed structure for static type table‐top floating image system with horizontal parallax function

A new structure of horizontal parallax table‐top floating image system with toroidal‐lens optical film was developed. In this design, the circular arranged pico‐projectors limit the angular resolution of this system and display the floating image for surrounding viewing zones. In addition, the pinhole array and toroidal‐lens layer compose the optical film in the system and correspond with each other; both of them could be considered as a repeatable unit to control the spatial resolution of image. After passing through the optical film, the direction, position, shape, and divergence angle of light field could be controlled as fan ray, which has a widely scattered angle in latitude and high directivity in longitude direction. Moreover, to confirm the optical properties, the proposed structure was built in the commercially optical software, LightTools v8.3, which is widely used in the simulation of light distribution. Based on the imaging principle and the inverse light tracking method, displaying floating image with circular viewing zones would be achieved.     

Determination of luminance distribution of autostereoscopic 3D displays through calculation of angular profile

Abstract— The luminance distribution of autostereoscopic 3‐D displays using the parallax‐barrier method was simulated by two different calculation methods. The first method directly calculates the total luminance distribution by summing light rays coming from different positions on the imaging display through a parallax barrier at each eye position. The second method first calculates the angular distribution of light rays coming from the imaging display through a parallax barrier and then derives the spatial luminance distribution for each eye position. The two methods resulted in an equivalent distribution. Yet, the second method outperforms the first method in terms of calculating the speed and versatility.     

Robust Image Denoising Using a Virtual Flash Image for Monte Carlo Ray Tracing

We propose an efficient and robust image‐space denoising method for noisy images generated by Monte Carlo ray tracing methods. Our method is based on two new concepts: virtual flash images and homogeneous pixels. Inspired by recent developments in flash photography, virtual flash images emulate photographs taken with a flash, to capture various features of rendered images without taking additional samples. Using a virtual flash image as an edge‐stopping function, our method can preserve image features that were not captured well only by existing edge‐stopping functions such as normals and depth values. While denoising each pixel, we consider only homogeneous pixels—pixels that are statistically equivalent to each other. This makes it possible to define a stochastic error bound of our method, and this bound goes to zero as the number of ray samples goes to infinity, irrespective of denoising parameters. To highlight the benefits of our method, we apply our method to two Monte Carlo ray tracing methods, photon mapping and path tracing, with various input scenes. We demonstrate that using virtual flash images and homogeneous pixels with a standard denoising method outperforms state‐of‐the‐art image‐space denoising methods.     

A new Maxwellian view display for trouble‐free accommodation

We studied a new display system that realizes a Maxwellian view. The system is composed of a base display and a fly‐eye lens with micro‐pinholes. This forms ray intersecting points of diameter of 0.8 mm at a viewing distance of 280 mm. It was confirmed that the new display system can extend the depth of field of the human eye system, where the observer sets the ray intersecting point at his pupil.     

Realistic computer graphics and free form surfaces

An image generation approach in computer graphics leading to images of considerable optical quality is ray tracing, deduced from geometric optics. Crucial for the efficiency of ray tracing is to find quickly an intersection point closest to a ray's origin. This requires to restrict the candidate patches of a given scene as well as to find the intersections of a ray with a patch. We survey approaches to solve these two problems, and present a new method, based on space sweep and patch subdivision. Its advantages are subdivision adapted to the distribution of rays and consideration of ray coherence. This implies that useless subdivisions are avoided.     

Discrete ray tracing

Discrete ray tracing, or 3-D raster ray tracing (RRT), which, unlike existing ray tracing methods that use geometric representation for the 3-D scene employs a 3-D discrete raster of voxels for representing the 3-D scene in the same way a 2-D raster of pixels represents a 2-D image, is discussed. Each voxel is a small quantum unit of volume that has numeric values associated with it representing some measurable properties or attributes of the real object or phenomenon at that voxel. It is shown that RRT operates in two phases: preprocessing voxel and discrete ray tracing. In the voxel phase, the geometric model is digitized using 3-D scan-conversion algorithms that convert the continuous representation of the model into a discrete representation within the 3-D raster. In the second phase, RRT employs a discrete variation of the conventional recursive ray tracer in which 3-D discrete rays are traversed through the 3-D raster to find the first surface voxel. Encountering a nontransparent voxel indicates a ray-surface hit. Results obtained by running the RRT software one one 20-MIPS (25-GHz) processor of a Silicon Graphics 4D/240GTX are presented in terms of CPU time     

Image correction based on homography in stereoscopic projection display

Abstract— Stereoscopic and autostereoscopic projection‐display systems use projector arrays to present stereoscopic images, and each projector casts one parallax image of a stereoscopic scene. Because of the position shift of the projectors, the parallax images have geometric deformation, which influences the quality of the displayed stereoscopic images. In order to solve this problem, a method based on homography is proposed. The parallax images are pre‐transformed before they are projected, and then the stereoscopic images without geometric distortion can be obtained. An autostereoscopic projection‐display system is developed to present the images with and without calibration. Experimental results show that this method works effectively.     

LC GRIN lens mode with wide viewing angle for rotatable 2D/3D tablet

To widen the vertical and horizontal angular ranges where the lens performs well, the off‐axis performance of a liquid crystal gradient index (LC GRIN) lens is analyzed by the combined simulation system of an LC director simulator and a ray‐tracing simulator. We found that the angular difference between an LC alignment direction and an electrode array direction of the LC GRIN lens is one of significant parameters, and detailed conditions of structure are established. The measurement result shows that the developed structure reduces the degradation ratio in a luminance profile from 61% to 3.2%. We have applied a user tracking system for the rotatable 3D display, equipped with a detection of a panel orientation and a face position. As a result, we have developed a rotatable 2D/3D tablet whose 3D viewing azimuth angle is over 30° in both landscape and portrait orientations.     

Parallel processing of incremental ray tracing on a shared-memory multiprocessor

This paper presents a novel parallel-processing method for image synthesis using incremental ray tracing on a shared-memory multiprocessor workstation. The most efficient technique for image synthesis is ray tracing, proposed by Whitted in 1980. Ray-tracing algorithms are simple and can generate realistic images. However, they are time-consuming, since calculations of the intersections between objects and ray increase exponentially as the complexity of scenes increases. Fast image synthesis for animation is one of the most important topics in computer graphics. As the area of computer applications has broadened, the complexity of images to be synthesized has increased. Parallel processing of computer graphics is one way of achieving fast image synthesis. This paper describes a parallel processing technique for incremental ray tracing, which recalculates only the rays changed by moving objects in successive scenes of continuous image synthesis. The performance of parallel ray tracing was evaluated on the multiprocessor workstation TOP-1. Strategies for allocating pixels to processes under a multiprocess operating system on this workstation are discussed.     

Viewing angle enhanced integral imaging display based on double‐micro‐lens array

A viewing angle enhanced integral imaging display, which consists of a double microlens array, and a display panel is proposed. The double microlens array includes a convex microlens array and a concave microlens array. The display panel is used to display original elemental image array. The convex microlens array, located near the display panel, is used to provide a virtual elemental image array for the concave microlens array. The concave microlens array, located far away from the display panel, is used to display integral images with the virtual elemental image array. Compared with the original elemental image, the pitch for each virtual elemental image is magnified by the corresponding convex microlens. As a result, the viewing angle is expanded. Simulations based on ray‐tracing are performed and the results agree well with the theory.     

双目区域视差快速计算及测距算法

目的 双目测距对水面无人艇自主避障以及视觉侦察具有重要意义,但视觉传感器成像易受光照环境及运动模糊等因素的影响,基于经典Census变换的立体匹配代价计算方法耗时长,且视差获取精度差,影响测距精度。为了提高测距精度并保证算法运行速度,提出一种用于双目测距的快速立体匹配算法。方法 基于传统Census变换,提出一种新的比特串生成方法,在匹配点正方形支持窗口的各边等距各选3个像素点,共选出8个像素点,这8个像素点两两比较生成一个字节的比特串。将左右视场中的匹配点与待匹配点的比特串进行异或,得到两点的汉明距离,在各汉明距离中找到距离最小的像素点作为匹配像素点,两像素点的横坐标差为视差。本文采用区域视差计算的方法,在左右视场确定同一目标区域后进行视差提取和滤波,利用平均视差计算目标的距离。结果 本文算法与基于传统Census变换的立体匹配视差获取方法相比,在运算速度方面优势明显,时间稳定在0.4 s左右,用时仅为传统Census变换算法的1/5。在Middlebury数据集中的图像对teddy和cones上进行的算法运行时间对比实验中,本文基于Census变换改进的算法比已有的基于Census变换的匹配算法在运行时间上快了近20 s。在实际双目测距实验中,采用本文算法在1019 m范围内测距误差在5%以内,根据无人艇的运动特点和避障要求,通过分析可知该算法的测距精度可以满足低速无人艇的避障需求。结论 本文给出的基于改进Census变换的匹配算法在立体匹配速度上有大幅提高,提取目标视差用于测距,实际测距结果表明,本文算法能够满足水面无人艇的视觉避障要求。     

The effect of stereoscopic viewing in a word‐search task with a layered background

Abstract— The benefits of stereoscopic viewing were explored in searching in words superimposed over a background. In the first experiment, eight participants searched for text in a normal 2‐D display, a 3‐D display using a parallax barrier, and a darkened 2‐D display of equivalent brightness to the 3‐D display. Word‐search performance was significantly faster for the bright 2‐D display vs. the 3‐D display, but when brightness was controlled, performance on the 3‐D display was better relative to the 2‐D (dim) display. In a second experiment, the effect of floating text vs. sinking background disparity was assessed across four background conditions. Twenty participants saw only the floating‐text (FT) condition and 20 participants saw only the sinking‐background (SB) condition. Performance of the SB group was significantly better than that of FT group, and the advantage of SB disparity was greater with the more‐complex backgrounds. Thus, when a parallax‐barrier 3‐D display is used to view text or other figural information overlaid on a background, it is proposed that the layer of primary interest (foreground) should be displayed with zero disparity (on the physical display surface) with the secondary layer (background) appearing to be sunk beneath that surface.     

Self‐calibration three‐dimensional light field display based on scalable multi‐LCDs

Approach to achieve self‐calibration three‐dimensional (3D) light field display is investigated in this paper. The proposed 3D light field display is constructed up on spliced multi‐LCDs, lens and diaphragm arrays, and directional diffuser. The light field imaging principle, hardware configuration, diffuser characteristic, and image reconstruction simulation are described and analyzed, respectively. Besides the light field imaging, a self‐calibration method is proposed to improve the imaging performance. An image sensor is deployed to capture calibration patterns projected onto and then reflected by the polymer dispersed liquid crystal film, which is attached to and shaped the diffuser. These calibration components are assembled with the display unit and can be switched between display mode and calibration mode. In the calibration mode, the imperfect imaging relations of optical components are captured and calibrated automatically. We demonstrate our design by implementing the prototype of proposed 3D light field display by using modified off‐the‐shelf products. The proposed approach successfully meets the requirement of real application on scalable configuration, fast calibration, large viewing angular range, and smooth motion parallax.     

A high‐resolution autostereoscopic display system with a wide viewing angle using an LCOS projector array

Abstract— This study develops an autostereoscopic display based on a multiple miniature projector array to provide a scalable solution for a high‐resolution 3‐D display with large viewing freedom. To minimize distortion and dispersion, and to maximize the modulation transfer function (MTF) of the projection image to optimize 3‐D image quality, a dedicated projection lens and an accurate six‐axis adjusting platform for the miniature projector were designed and fabricated. Image‐blending technology based on a lookup table was adopted to combine images from 30 miniature projectors into a seamless single image. The result was a 35‐in. autostereoscopic display with 60 views ata 30° viewing angle, 90° FOV, and large range of viewing distance. The proposed system exhibits very smooth motion parallax when viewers move around in front of it.     

Special relativistic visualization by local ray tracing

Special relativistic visualization offers the possibility of experiencing the optical effects of traveling near the speed of light, including apparent geometric distortions as well as Doppler and searchlight effects. Early high-quality computer graphics images of relativistic scenes were created using offline, computationally expensive CPU-side 4D ray tracing. Alternate approaches such as image-based rendering and polygon-distortion methods are able to achieve interactivity, but exhibit inferior visual quality due to sampling artifacts. In this paper, we introduce a hybrid rendering technique based on polygon distortion and local ray tracing that facilitates interactive high-quality visualization of multiple objects moving at relativistic speeds in arbitrary directions. The method starts by calculating tight image-space footprints for the apparent triangles of the 3D scene objects. The final image is generated using a single image-space ray tracing step incorporating Doppler and searchlight effects. Our implementation uses GPU shader programming and hardware texture filtering to achieve high rendering speed.     

An effective calibration procedure for correction of parallax unmatched image pairs

The stereo image pairs or two-view video sequences can be captured by two cameras at two horizontally different positions. If the stereo image pairs possess incompatible convergences of vertical parallax and horizontal parallax, human eyes generally cannot properly exhibit stereo visualisation. If the image pairs are taken from single camera or selected from a video sequence, perception of stereo visualisation will become even worse. The authors propose an effective calibration procedure to adjust the image pairs to achieve better stereo visualisation. The proposed calibration procedure contains six steps, including feature point extraction, bidirectional feature point matching, relative distance checking, image transformation, hole-filling and reshaping. Experimental results show that the proposed system can effectively adjust vertical and horizontal parallax such that the calibrated stereo image pairs can properly exhibit stereo scenes in stereoscopic display systems. Experimental results also reveal that the proposed method can achieve less vertical parallax than the existing rectification methods.     

Multi‐Layered Automultiscopic Displays

Our hybrid display model combines multiple automultiscopic elements volumetrically to support horizontal and vertical parallax at a larger depth of field and better accommodation cues compared to single layer elements. In this paper, we introduce a framework to analyze the bandwidth of such display devices. Based on this analysis, we show that multiple layers can achieve a wider depth of field using less bandwidth compared to single layer displays. We present a simple algorithm to distribute an input light field to multiple layers, and devise an efficient ray tracing algorithm for synthetic scenes. We demonstrate the effectiveness of our approach by both software simulation and two corresponding hardware prototypes.     

Real‐time Depth of Field Rendering via Dynamic Light Field Generation and Filtering

We present a new algorithm for efficient rendering of high‐quality depth‐of‐field (DoF) effects. We start with a single rasterized view (reference view) of the scene, and sample the light field by warping the reference view to nearby views. We implement the algorithm using NVIDIA's CUDA to achieve parallel processing, and exploit the atomic operations to resolve visibility when multiple pixels warp to the same image location. We then directly synthesize DoF effects from the sampled light field. To reduce aliasing artifacts, we propose an image‐space filtering technique that compensates for spatial undersampling using MIP mapping. The main advantages of our algorithm are its simplicity and generality. We demonstrate interactive rendering of DoF effects in several complex scenes. Compared to existing methods, ours does not require ray tracing and hence scales well with scene complexity.