Seamless ultrathin rear projection display

A new architecture for a thin (2‐cm depth) rear projection display is described. In order to achieve this small depth, a very high density of rear projectors is used. Three prototype displays using rear projectors on both 5‐ and 2‐cm pitch arrays are described. The displays can achieve an effective screen pixel pitch of as small as 0.5 mm, which makes this technology competitive in terms of resolution with fine pitch LED displays; however, orders of magnitude fewer LEDs are required: Each rear projector requires only one white LED and a color liquid crystal light modulator. In the three prototypes, the projector light modulators utilize 101‐cm (40 in.), 80‐cm (31.5 in.), and 60‐cm (24 in.) diagonal liquid crystal display glass. To minimize cost, no lenses are utilized for the rear projectors. An RGB LED array may augment the projector array, which provides a low resolution component of the image onto which the high resolution component is superimposed by the projector array. Edge gaps between active areas on adjacent LCD glass units are completely eliminated by the rear projection approach enabling low profile wall‐size seamless displays. Display contrast depends on rear projection screen design.     

基于单投影仪与柱面反射镜的沉浸感显示系统

在分析传统沉浸感显示系统优缺点的基础上,设计并实现了一种新型的沉浸感显示系统。该系统使用柱面反射镜对单投影仪投射光线进行反射,并在弧形背投幕上成像,能够获得无缝画面,实现了广角度虚拟场景的连贯显示。通过合理设计柱面反射镜形状,实现了投影画面在水平方向上的均匀放大。通过对图像进行预变形可以基本消除因投影幕曲率而产生的投影画面形变,同时采用背投技术使参与者在虚拟场景中活动更加自如。该系统克服了传统的多投影仪或多显示器沉浸感显示系统中存在的图像拼接问题,且易于构建,经实验验证能够获得良好的沉浸感显示效果。     

Microdisplay‐based optical module for avionic display applications

Abstract— A new optical scheme for a LCOS‐based rear‐projection system utilizing an LED illumination source is presented. The proposed optical module could conveniently replace conventional aircraft panel instrumentation not only because it achieves major standard avionics application requirements, such as the capability to withstand mechanical shocks, high reliability, and weight and power‐consumption minimization, but also as a consequence of the fact that it allows the display image area to be properly matched to the shape of the instrument panel more easily than with conventional displays.     

Fully digital LCoS device for consumer applications

Abstract— This paper presents a new display device, which combines a digital backplane and a vertically aligned nematic liquid‐crystal layer. The device has 1280 × 720 pixels in a 0.7‐in.‐diagonal display area. In this paper, we present the concept of the new device and overview the performance of the device for a rear‐projection television application.     

Moiré interference in multilayered displays

Abstract— Multi‐layered displays contain a pair of parallel liquid‐crystal‐display panels spaced apart from each other. The viewer sees objects displayed on the front and rear layers to form a three‐dimensional image. Each layer has an array of pixels arranged in an RGB striped configuration. When imaged on the retina, the layers interact to produce a beat pattern referred to as moiré. This pattern can be distracting to people seeking to use a multi‐layered display. To solve this problem, the high‐frequency components on the rear most display are attenuated using an interstitial optical diffuser. Given the characteristics of the diffuser and imaging planes, a function is derived to calculate the amount of residual moiré interference present. A measurement device and methodology was constructed to quantify the amplitude of the beat pattern and the blur on the rear image plane in terms of the human visual system.     

Optical simulation for cross‐talk evaluation and improvement of autostereoscopic 3‐D displays with a projector array

Abstract— Multi‐view spatial‐multiplexed autostereoscopic 3‐D displays normally use a 2‐D image source and divide the pixels to generate perspective images. Due to the reduction in the resolution of each perspective image for a large view number, a super‐high‐resolution 2‐D image source is required to achieve 3‐D image quality close to the standard of natural vision. This paper proposes an approach by tiling multiple projection images with a low magnification ratio from a microdisplay to resolve the resolution issue. Placing a lenticular array in front of the tiled projection image can lead to an autostereoscopic display. Image distortion and cross‐talk issues resulting from the projection lens and pixel structure of the microdisplay have been addressed with proper selection of the active pixel and adequate pixel grouping and masking. Optical simulation has shown that a 37‐in. 12‐view autostereoscopic display with a full‐HD (1920 × 1080) resolution can be achieved with the proposed 3‐D architecture.     

最大投影栅缝法检测文档图像倾斜角

针对由照相机扫描仪等文档获取设备拍摄的文档图像可能存在倾斜,进而导致光学字符识别（OCR）软件不能正确识别的情况,采用了一种以文档图像投影栅缝宽为目标函数的优化方法,栅缝宽最大值对应的投影角度的相反数即为文档图像的倾斜角。利用栅线宽函数扩大了检测范围,并提高了检测速度;利用反投影法和均布列预投影等方法,减少了计算量;利用二分法提高了算法的检测精度。通过一些包含少量插图的文档图像的倾斜角检测实验,验证了该方法的有效性。     

The auto‐geometric correction of multi‐projector for cylindrical surface using Bézier patches

Geometric calibration to projection images is an indispensable operation for projection‐based spatial display. In this paper, we propose a new method for correcting images generated in a computer onto a cylindrical surface accurately, which can project a high‐resolution projection image with pixels matching avoiding too much manual operation. Images waiting to be projected are pre‐warped according to the rough correspondence between projectors and physical surface. To solve the errors resulting from unexpected pixel shifts in overlap projection area, we fit the Bézier interpolation to the images and apply the optimization theory with added constraints to correct the projection image accurately. This optimization process, by taking the pixels with specific significance on the images as the basis of calculation, avoids the traditional ways of translating the control points of the Bézier surface directly. The final results achieve a completely accurate projection picture even if the projection surface shape is inaccurate and irregular. We present the details of the proposed accurate calibration algorithm and illustrate our method, which, with its scalability, can achieve perfect projection efficiently and accurately with experiments.     

Polarization‐independent modulation for projection displays using small‐period LC polarization gratings

Abstract— Progress in the use of liquid‐crystal polarization grating (LCPG) to modulate unpolarized (and polarized) light with a grating period as small as 6.3 μm is reported. Similar to LCPGs formed at larger periods (11 μm) reported previously, polarization‐independent switching, predominantly three diffraction orders, maximum contrast ratios of ～100:1 for unpolarized broadband light, very low scattering, and diffraction efficiencies >98% continue to be observed. The smaller period led to an expected lower threshold voltage, even though the thickness was greater. Because the smaller grating period enables a brighter result from a Schlieren projection scheme for a microdisplay using the LCPG light valve, the inherent tradeoffs involved with both material and design parameters are discussed, and prospects for a polarization‐independent projection display are commented upon.     

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.     

The Zenithal Bistable Display: From concept to consumer

Abstract— The first commercial use of the Zenithal Bistable Display (ZBD?) is for electronic point‐of‐purchase (epop?) signage in the retail sector. As a reflective bistable display, this novel LCD technology only consumes power if new information is required and the image is updated. This allows complex images to be shown constantly for several years from the energy of a single low‐cost battery, when the display is updated up to ten times each day — ideal for signage applications. Excellent performance characteristics are achieved in a TN‐like STN‐LCD in which one of the alignment surfaces is a relief grating. Correct design of the grating shape and surface properties not only imparts the bistability, but allows control of the optical performance, the latching voltages, and the temperature range. Being addressed using a simple passive‐matrix approach, without the need for a thin‐film‐transistor backplane, large amounts of information may be displayed by STN drivers. Alow‐cost fabrication method has been devised that is compatible with conventional TN and STN manufacture, and with negligible equipment outlay. The device operating principles, manufacturing method, and performance of ZBDs are reviewed.     

High‐resolution autostereoscopic 3‐D projection display with a space‐dividing iris‐plane shutter

Abstract— A high‐resolution autostereoscopic 3‐D projection display with a polarization‐control space dividing the iris‐plane liquid‐crystal shutter is proposed. The polarization‐control iris‐plane shutter can control the direction of stereo images without reducing the image quality of the microdis‐play. This autostereoscopic 3‐D projection display is 2‐D/3‐D switchable and has a high resolution and high luminance. In addition, it has no cross‐talk between the left and right viewing zones, a simple structure, and the capability to show multi‐view images.     

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.     

Floating autostereoscopic display with in situ interaction

Floating three‐dimensional (3D) display implements direct interaction between human hands and virtual 3D images, which offers natural and effective augmented reality interaction. In this study, we propose a novel floating autostereoscopic display, combining head tracking lenticular display with an image projection system, to offer the observers with an accurate 3D image floating in midair without any optical elements between observers and the virtual 3D image. Combined with a gesture recognition device, the proposed system can achieve in situ augmented reality interaction with the floating 3D image. A distortion correction method is developed to achieve 3D display with accurate spatial information. Moreover, a coordinate calibration method is designed to improve the accuracy in the in situ interaction. Experiments were performed to prove the feasibility of the proposed system, and the good results show the potential of human‐computer interaction in medicine and life sciences.     

A high‐contrast front‐projection display system optimizing the projected light‐angle range

Abstract— The problem with front‐projection displays is that the screen contrast ratio decreases under bright‐ambient conditions. To overcome this problem, the design of a special screen, composed of the diffuser whose diffusing property shows top‐hat characteristics and a sawtooth reflector, is proposed. The screen diffuses the incident image light arriving at a projection‐angle range that is a lower‐angle range than the viewing‐angle range, and reflects the ambient light out of the viewing‐angle range. In this paper, the projection‐angle range and the viewing‐angle range was optimized to improve the contrast ratio of a front‐projection display. As a result, a special screen with the above‐mentioned diffusing property was realized, and a high‐quality front‐projection display with a high contrast ratio, even in a bright room, was achieved.     

Refractive‐reflective optical system for realizing an ultra‐thin rear projector

Abstract— This paper presents a new optical system used in an ultra‐thin rear projector with a 1500‐mm diagonal size and 260‐mm depth. A refractive‐reflective optical system was developed to achieve a large projection angle of 136° with a small optical distortion of 0.1%. The optics consists of a convex aspherical mirror and a refractive lens. In addition, a new Fresnel screen composed of hybrid blades of refractive‐TIR (total internal reflection) elements was developed to attain good uniformity of brightness and color within the image area.     

Competing display technologies for the best image performance

Abstract— Cathode‐ray tubes (CRTs) have been the dominant display technology for years, having the best image performance and low cost. During the last several years, flat‐panel‐display technologies, such as liquid‐crystal displays (LCDs), began to replace the CRT mainly because of its favorable form factor. Today, the image performance of LCDs are equal to that of a CRT, and attractive flat‐display products have become so affordable that they have replaced the CRT from its dominating market position and have obtained the largest market share. In the past, the CRT set the standards for digital imaging technologies, but today, modern image capturing, storage, transport, signal processing, and printing technologies have improved to such high levels that they demand better display technologies and standards. At present, the LCD is at the forefront of this display‐technology evolution. This paper will focus on the latest image‐quality improvements in LCD technology and briefly touch alternatives such as plasma‐display panels (PDP) and microdisplay projection. Special attention will be given to the latest developments in wide‐color‐gamut technologies and methods to reproduce accurate colors within a display device.     

Projection‐type integral 3‐D display with distortion compensation

Abstract— Our research is aimed at developing a spatial‐imaging‐type integral three‐dimensional (3‐D) display based on an integral photography method using an extremely high‐resolution projector. One problem with the projection‐type integral 3‐D display is that geometrical distortion in projected elemental images causes spatial deformation of the displayed 3‐D image. In this study, a general relationship between the geometric distortion of elemental images and the spatial deformation of reconstructed 3‐D images were analyzed. A projection‐type integral 3‐D display with a distortion compensator which corrects the geometrical distortions of projected images in real‐time have been developed. The deformation of the displayed 3‐D images was significantly reduced by the distortion compensation, and the displayed 3‐D images had a resolution of 182 (H) × 140 (V) pixels and a viewing angle of 24.5°.     

Image modification for immersive projection display based on pseudo‐projection models

This paper describes a practical method that enables actual images to be converted so that they can be projected onto an immersive projection display (IPD) screen. IPD screens are particularly unique in that their angle of view is extremely wide; therefore, the images projected onto them need to be taken on a special format. In practice, however, it is generally very difficult to shoot images that completely satisfy the specifications of the targeting IPD environment due to cost, technical problems or other reasons. To overcome these problems, we developed a method to modify the images by abandoning geometrical consistency. We were able to utilize this method by assuming that the given image was shot according to a special projection model. Because this model differed from the actual projection model with which the image was taken, we termed it the pseudo‐projection model. Since our method uses simple geometry, and can easily be expressed by a parametric function, the degree of modification or the time sequence for modification can readily be adjusted according to the features of each type of content. Copyright © 2003 John Wiley & Sons, Ltd.     

光栅投影式3维照相系统中光栅投影仪的标定

提出了一种光栅投影式立体照相系统中光栅投影平面的标定方法。将光栅投影到已知目标平面,通过数字摄影得到光栅平面与目标平面相交的光栅图像。根据光栅图像记录的信息,在每条交线上提取两点,作为对应光栅平面拟合用的两点。按一定规律移动目标平面,即可得到每个光栅平面上若干对点。利用最小二乘法分别拟合出每个光栅平面的空间平面方程。