Processes,characterizations, and system applications of color‐filter liquid‐crystal‐on‐silicon microdisplays

Abstract— A color‐filter liquid‐crystal‐on‐silicon (CF‐LCOS) microdisplay that integrates color filters on silicon for color will be presented. The color‐filter process on silicon was optimized to achieve fine resolution and precise alignment of the color filters on the pixel array, good adhesion to the silicon suface, and a flat surface for the liquid‐crystal cell assembly. Important optical and electrical parameters of the color filters were extracted to establish an electro‐optical model of the CF‐LCOS microdisplays for device simulation. Thermal, chemical, and light‐stability characterizations were performed to ensure the stabilty of the color filters and CF‐LCOS microdisplays. With color CF‐LCOS microdisplays already available, the projection or viewing optics is greatly simplified. This CF‐LCOS microdisplay is ideal for near‐to‐eye displays because of its low‐power consumption and compactness. The CF‐LCOS microdisplay could also withstand medium light illumination for medium‐sized projectors. A single‐panel projector based on one CF‐LCOS microdisplay of 1280 × 768 × RGB resolution was demonstrated.     

Projection‐based head‐tracking 3‐D displays

Abstract— This paper describes the construction and operation of four 3‐D displays in which each display produces two images for each eye and thus fits into the category of projection‐based binocular stereoscopic displays. The four 3‐D displays described are pico‐projector‐based, liquid‐ crystal—on—silicon (LCOS) conventional projector‐based, 120‐Hz digital‐light‐processor (DLP) projector‐ based, and the HELIUM3D system. In the first three displays, images are produced on a direct‐view LCD whose conventional backlight is replaced with a projection illumination source that is controlled by a multi‐user head tracker; novel steering optics direct the projector output to regions referred to as exit pupils located at the viewers' eyes. In the HELIUM3D display, the image information is supplied by a horizontally scanned, fast, light valve whose output is controlled by a spatial light modulator (SLM) to direct images to the appropriate viewers' eyes. The current statu s and the multimodal potential of the HELIUM3D display are described.     

Advances towards high‐resolution pack‐and‐go displays: A survey

Abstract— Tiled displays provide high resolution and large scale simultaneously. Projectors can project on any available surface. Thus, it is possible to create a large high‐resolution display by simply tiling multiple projectors on any available regular surface. The tremendous advancement in projection technology has made projectors portable and affordable. One can envision displays made of multiple such projectors that can be packed in one's car trunk, carried from one location to another, deployed at each location easily to create a seamless high‐resolution display, and, finally, dismantled in minutes to be taken to the next location — essentially a pack‐and‐go display. Several challenges must be overcome in order to realize such pack‐and‐go displays. These include allowing for imperfect uncalibrated devices, uneven non‐diffused display surfaces, and a layman user via complete automation in deployment that requires no user invention. We described the advances we have made in addressing these challenges for the most common case of planar display surfaces. First, we present a technique to allow imperfect projectors. Next, we present a technique to allow a photometrically uncalibrated camera. Finally, we present a novel distributed architecture that renders critical display capabilities such as self‐calibration, scalability, and reconfigurability without any user intervention. These advances are important milestones towards the development of easy‐to‐use multi‐projector displays that can be deployed anywhere and by anyone.     

MUTED: Multi‐user 3‐D display

Abstract— Research described in this paper encompasses the design and building of glasses‐free (autostereoscopic) displays that utilize a direct‐view liquid‐crystal display whose backlight is provided by a projector and novel steering optics. This is controlled by the output of a multi‐user head‐position tracker. As the displays employ spatial multiplexing on a liquid‐crystal‐display screen, they are inherently 2‐D/3‐D switchable with 2‐D being achieved by simply displaying the same image in the left and right channels. Two prototypes are described in this paper; one incorporating a holographic projector and the other a conventional LCOS projector. The LCOS projector version addresses the limitations of brightness, cross‐talk, banding in the images, and laser stability that occur in the holographic projector version. The future development is considered and a comparison between the prototypes and with other 3‐D displays is given.     

Projection displays: New technologies,challenges, and applications

The achievable color gamut and light output of projection displays based on light‐emitting diodes (LEDs), phosphor conversion, and lasers are discussed. The color appearance phenomena, colorfulness, and the Helmholtz–Kohlrausch effect are discussed in the context of LED and laser illumination of projection displays, as well as some pitfalls concerning the interpretation of the Helmholtz–Kohlrausch effect. Also the laser speckle phenomenon and the characterization of it are addressed. The importance of both the American National Standards Institute (ANSI) contrast and the sequential contrast of projectors, as well as the discrepancy between measured and perceived contrasts, are explained. Visibility criteria for contouring artifacts are explained and compared with new emerging electro‐optical transfer functions that are more adapted to this issue. Stereoscopic solutions and early prototypes of autostereoscopic multi‐view, super multi‐view projection displays, and electro‐holographic displays are discussed as well as the limiting factors of these systems in the context of display resolution, and LED and laser light sources.     

投影仪光路仿真系统

近年来,随着计算机技术的高速发展,建立以计算机集群为驱动的多通道投影技术已经越来越成熟。多通道投影技术是指采用多台投影机组合而成的多通道大屏幕显示系统。为了解决投影仪位置摆放问题,设计一套投影仪光路仿真系统。在未建立荧幕的情况下确定投影仪的位置。     

Full‐parallax autostereoscopic display with scalable lateral resolution using overlaid multiple projection

Abstract— A method to increase the viewing resolution of an autostereoscopic display without increasing the density of microlenses is proposed. Multiple projectors are used for the projection images to be focused and overlaid on a common plane in the air behind the microlens array. The multiple overlaid projection images yield multiple light spots inside the region of each elemental lenslet of the microlens array. This feature provides scalable high‐resolution images by increasing the number of projectors. Based on the proposed method, a prototype display that includes 15 projectors was designed and built. 3‐D images were successfully reproduced on the prototype display with full parallax and a wide viewing angle of 70°.     

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。     

Parametric study using distributed computing and genetic algorithm in TFT‐LCD projector

We present an analysis of the parameters affecting light engines in liquid crystal display (LCD) projectors, using actual LCD projectors as examples. The significant parameters affecting light engines in LCD projectors are evaluated using the light uniformity as the determining standard. Optimization is performed on those parameters that affect the uniformity as well as the rendering effects of the projectors, by employing our own distributed genetic algorithm. The rotation angle of the collimator and its position are shown to improve the uniformity of the LCD projection, but we find that their effect on improving the brightness is not significant. Increased length of a projectors' light tube promotes better integration results. In our study, we effectively improved the performance index of an LCD projector, increasing projection uniformity by 4% (to 91.5%) and the brightness by 12% (to 7.9 lm).     

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.     

Registration techniques for using imperfect and partially calibrated devices in planar multi-projector displays

Multi-projector displays today are automatically registered, both geometrically and photometrically, using cameras. Existing registration techniques assume pre-calibrated projectors and cameras that are devoid of imperfections such as lens distortion. In practice, however, these devices are usually imperfect and uncalibrated. Registration of each of these devices is often more challenging than the multi-projector display registration itself. To make tiled projection-based displays accessible to a layman user we should allow the use of uncalibrated inexpensive devices that are prone to imperfections. In this paper, we make two important advances in this direction. First, we present a new geometric registration technique that can achieve geometric alignment {\em in the presence of severe projector lens distortion} using a relatively inexpensive low-resolution camera. This is achieved via a closed-form model that relates the projectors to cameras, in planar multi-projector displays, using rational Bezier patches. This enables us to geometrically calibrate a 3000 x 2500 resolution planar multi-projector display made of 3 x 3 array of nine severely distorted projectors using a low resolution (640 x 480) VGA camera. Second, we present a photometric self-calibration technique for a projector-camera pair. This allows us to photometrically calibrate the same display made of nine projectors using a photometrically uncalibrated camera. To the best of our knowledge, this is the first work that allows geometrically imperfect projectors and photometrically uncalibrated cameras in calibrating multi-projector displays.     

Color and brightness appearance issues in tiled displays

Large-format displays created by tiling multiple, projected images have been used for decades in flight simulators and entertainment and are commercially available in a variety of forms. More recently, various research organizations have built custom display walls out of commodity projectors to support research in visualization, large-format display, and interaction. In these settings, making the display appear as a single, seamless surface has proven challenging. Where tiles overlap, they create bright seams. The tiles vary in color and brightness, not only from tile to tile, but within each tile. Each projector has a slightly different color gamut, caused by variations in the bulb, color filters, and digital processing (contrast, brightness, and gamma) for the projector. The spatial variation in brightness has two causes. First, the light from a projection system doesn't uniformly illuminate the screen. Second, the light doesn't scatter uniformly out of the front of the screen, making the perceived brightness depend on the viewing angle. In some projectors, the projected light's color also varies across the tile's face, resulting in unwanted tints in the images. I describe what causes these variations and what can be done about them     

Thin flexible photosensitive cholesteric displays

Abstract— A novel optically addressable, flexible bistable cholesteric liquid‐crystal display (ChLCD) is presented. These displays utilizeazo‐binaphthalene photosensitive chiral dopants that undergo photo‐isomerization upon exposure to light. The isomerization results in a change in the pitch of the cholesteric liquid crystal (ChLC), which enables the creation of inherently high‐resolution light‐weight displays that are optically written. The displays can be photo‐addressed without patterned electrodes or complex addressing schemes. Capitalizing on the dynamic pitch and the bistability of photosensitive ChLCDs, the display is switched with a single pulse at a specific single voltage to drive the region of the display with a shorter pitch to the focal‐conic texture and the region of the display with a longer pitch to the planar texture. Once in the different textures, the display can hold an image indefinitely regardless of ambient lighting. As such, these displays are a natural fit for badges, shelf‐labels, and point‐of‐sale cards. In this paper, the photosensitive properties of an encapsulated display system in comparison to an unencapsulated display system is discussed. Properties such a photosensitivity, thermal relaxation, and electro‐optical response are studied and reported. In addition, a flexible optically addressable ChLCD is developed and demonstrated.     

Automatic Registration of Multi‐Projector Domes Using a Single Uncalibrated Camera

In this paper we present a novel technique for easily calibrating multiple casually aligned projectors on spherical domes using a single uncalibrated camera. Using the prior knowledge of the display surface being a dome, we can estimate the camera intrinsic and extrinsic parameters and the projector to display surface correspondences automatically using a set of images. These images include the image of the dome itself and a projected pattern from each projector. Using these correspondences we can register images from the multiple projectors on the dome. Further, we can register displays which are not entirely visible in a single camera view using multiple pan and tilted views of an uncalibrated camera making our method suitable for displays of different size and resolution. We can register images from any arbitrary viewpoint making it appropriate for a single head‐tracked user in a 3D visualization system. Also, we can use several cartographic mapping techniques to register images in a manner that is appropriate for multi‐user visualization. Domes are known to produce a tremendous sense of immersion and presence in visualization systems. Yet, till date, there exists no easy way to register multiple projectors on a dome to create a high‐resolution realistic visualizations. To the best of our knowledge, this is the first method that can achieve accurate geometric registration of multiple projectors on a dome simply and automatically using a single uncalibrated camera.     

Non‐planar projection performance evaluation and projector pose optimization

In projector applications, the actual display effect is primarily dependent on two aspects: projector performance parameters (intrinsic properties), and projector placement (extrinsic properties). Many studies have been conducted on the impact of the original resolution, illumination, and contrast ratio on projection performance. However, few studies have focused on the influence of extrinsic properties, including the position and orientation of the projector on the projection effect. In this paper, three projection performance evaluation criteria—projection resolution, resolution difference, and projection distance difference—are proposed in terms of extrinsic properties. Based on these evaluation criteria, a projection performance evaluation function was constructed. Through this function, as well as optimization employing the multi‐start and Monte Carlo methods, projector pose parameters corresponding to optimal projection effects can be obtained. Evaluations demonstrated that the proposed projection performance evaluation criteria could correctly describe the impacts of projector placement on projection effects. Projection systems arranged according to the projector pose optimization methods achieved good performance on screens in difference shapes with different numbers of projectors, where the resolution and display improved with no change of projector hardware parameters. The optimal projector poses calculated using these optimization methods can provide theoretical guidance for practical projector placement.     

Development of a parameterization image stitching algorithm for ultrashort throw laser MEMS projectors

We present a novel design of a parameterization image stitching algorithm for ultrashort throw laser MEMS projectors. The resultant method allows the use of projectors with short or even long throw ratios to achieve ultrashort throw projection through a parameterized algorithm to stitch multiple images into one single frame, alleviating the trade‐off between the resolution and frame rate in conventional laser MEMS displays. To evaluate the effectiveness, we construct a test system that consists of three off‐the‐shelf projectors with a throw ratio of 1.3 and three planar reflective mirrors. Using our method, the integrated system yields an ultrashort throw ratio of 0.26, greatly reducing the projection distance from 12 to 2.6 ft for the 120‐in. screen in diagonal. Moreover, our algorithm can be fine‐tuned to correct for image distortion, intensity variation, and edge mismatch induced by two‐axis light beam steering, thereby further improving the image quality.     

Color‐tuning projection system for adaptive combination of high brightness and wide color gamut

Abstract— The demand for projectors with high brightness and wide color gamut has been increasing; however, UHP lamp projectors cannot deliver those two qualities efficiently and simultaneously because of its color‐separation system. The newly developed projection system — “Color‐Tuning Projection System” — realizes the adaptive combination of high brightness and wide color gamut with one projector. This projector features a fourth liquid‐crystal panel — “Color Tuner” — with a 3LCD optical engine, which controls yellow light separately from the RGB light of a UHP lamp. This color‐tuner‐based optical engine — “Color‐Tuning Optical Engine” — and a new color‐conversion signal‐processing algorithm — “Adaptive Color Conversion Algorithm” — controls the yellow‐light volume and corrects color‐shifted pixels according to the brightness and chromaticity analysis of the input image, key technologies of the Color‐Tuning Projection System. This additional panel system enables the projector to ach ieve up to 115% higher brightness and 120% wider color gamut according to the input image. This paper presents an innovative design concept, a novel technology regarding brightness and a color‐gamut conversion projection system, and the characteristics of the prototype.     

Display grid: Ad‐hoc clusters of autonomous projectors

Abstract— Projectors, like computers, are becoming commoditized. Self‐contained computers are now being networked to create computing grids, allowing transparent access to a large computing resource or massive data storage. Image presentation devices can be similarly modified to support the concept of a “display grid” to create large seamless displays. Limiting ourselves to projector‐based display grids, we present techniques for creating multi‐projector displays via self‐configuring clusters of autonomous projectors. The ad‐hoc clustering approach avoids large monolithic installations. We show a low‐cost system that supports dynamic inclusion of new projectors, automatic geometric configuration, and seamless blending of overlapping projectors.     

3D Display Using Passive Optical Scatterers

A new class of 3D displays uses a digital projector and a cloud of passive optical scatterers etched in a glass cube with laser-induced damage.These inexpensive devices can be used to display simple 3D objects, extend videogames to three dimensions, and create 3D avatars. Over the past century, researchers have worked vigorously to create a device that can display realistic high-resolution 3D content. As an offshoot of that, we are developing an inexpensive class of volumetric displays that can present certain types of 3D content, including simple 3D objects, extruded objects, and 3D surfaces that appear dynamic when projected with time-varying images, at relatively low resolution. Our displays use a simple light engine and a cloud of passive optical scatterers. The basic idea is to trade off the light engine's 2D spatial resolution to gain resolution in the third dimension. One way to achieve such a tradeoff is to use a stack of planar grids of scatterers where no two stacks overlap each other with respect to the light engine's projection rays.     

A multi‐plane optical see‐through head mounted display design for augmented reality applications

Augmented reality (AR) display technology greatly enhances users' perception of and interaction with the real world by superimposing a computer‐generated virtual scene on the real physical world. The main problem of the state‐of‐the‐art 3D AR head‐mounted displays (HMDs) is the accommodation‐vergence conflict because the 2D images displayed by flat panel devices are at a fixed distance from the eyes. In this paper, we present a design for an optical see‐through HMD utilizing multi‐plane display technology for AR applications. This approach manages to provide correct depth information and solves the accommodation‐vergence conflict problem. In our system, a projector projects slices of a 3D scene onto a stack of polymer‐stabilized liquid crystal scattering shutters in time sequence to reconstruct the 3D scene. The polymer‐stabilized liquid crystal shutters have sub‐millisecond switching time that enables sufficient number of shutters to achieve high depth resolution. A proof‐of‐concept two‐plane optical see‐through HMD prototype is demonstrated. Our design can be made lightweight, compact, with high resolution, and large depth range from near the eye to infinity and thus holds great potential for fatigue‐free AR HMDs.