Bistable FLCOS devices for doubled‐brightness micro‐projectors

Abstract— Optical output is of paramount importance to emerging ultra‐miniature projector products. Experimental bistable ferroelectric liquid‐crystal‐on‐silicon (FLCOS) projection microdisplay devices using newly developed FLC materials aligned on obliquely deposited SiO₂ have been developed. These devices enable the doubling of the illumination duty cycle, and hence doubling of the achievable projector light output, while maintaining a DC‐balanced electrical drive.     

基于LabVIEW的投影机光学性能自动测试系统的设计

为了实现投影机光学性能测量的准确可靠,研制一套高精度、高效率的投影机光学性能自动测量系统.以运动控制卡、视频信号发生器、色彩照度计为硬件框架,以LabVIEW为软件平台进行开发.编制的测试软件串联起运动机构、信号源、数据采集等各部分,实现光度、色度等投影机光学性能的自动测量.随后利用计量校准、人工/自动测试对比实验分别对运动平台定位准确性、测试系统整体稳定性进行了验证.运动平台定位精度达到±0,1 mm;自动测试结果离散程度小,且实验标准偏差及极差均优于人工测试结果.实验结果表明:开发的投影机光学性能自动测量装置准确可靠.     

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.     

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.     

Makeup Lamps: Live Augmentation of Human Faces via Projection

We propose the first system for live dynamic augmentation of human faces. Using projector‐based illumination, we alter the appearance of human performers during novel performances. The key challenge of live augmentation is latency — an image is generated according to a specific pose, but is displayed on a different facial configuration by the time it is projected. Therefore, our system aims at reducing latency during every step of the process, from capture, through processing, to projection. Using infrared illumination, an optically and computationally aligned high‐speed camera detects facial orientation as well as expression. The estimated expression blendshapes are mapped onto a lower dimensional space, and the facial motion and non‐rigid deformation are estimated, smoothed and predicted through adaptive Kalman filtering. Finally, the desired appearance is generated interpolating precomputed offset textures according to time, global position, and expression. We have evaluated our system through an optimized CPU and GPU prototype, and demonstrated successful low latency augmentation for different performers and performances with varying facial play and motion speed. In contrast to existing methods, the presented system is the first method which fully supports dynamic facial projection mapping without the requirement of any physical tracking markers and incorporates facial expressions.     

Motion correction based on an appropriate system matrix for statistical reconstruction of respiratory-correlated PET acquisitions

Respiratory motion correction in positron emission tomography (PET) seeks to incorporate motion information into an image reconstruction algorithm by using the full counting statistics of an acquisition to generate a single, motion-free volume. Here, we present a motion-incorporated ordered subsets expectation maximization (MOSEM) reconstruction based on a device-dedicated tomographic projector in which each matrix element is calculated directly from the voxels’ Cartesian coordinates alone. The motion is corrected by updating this projector as a function of the respiratory level. The performance of the reconstruction method was investigated with three datasets: two simulations of a transaxially or axially moving lesion on a patient acquisition and a third acquisition of a moving sphere. After the 16th sub-iteration, the normalized mean square error (NMSE, with a motionless acquisition as reference) was 0.20 for the non-corrected (ungated) image and 0.01 for the MOSEM image with transaxial motion simulation. Likewise, NMSE was 0.30 for the ungated image and 0.03 for MOSEM image with axial motion simulation. For the phantom, ungated reconstruction yielded an error of 0.78, whereas MOSEM yielded 0.43. The error reduction resulted from enhancement and reduced spreading of the moving uptake. Our results show that MOSEM reconstruction yields motion-corrected images which are similar to motionless reference images.     

High‐efficiency optical system for ultra‐short‐throw‐distance projector based on multi‐laser light source

Abstract— A novel laser‐light‐source projector having the three outstanding features of high brightness, ultra‐short throw distance, and high color reproduction has been developed.These features have recently come to be required in the high‐end projector market. The technologies for the laser‐light‐source projectors fully utilize the advantages of lasers, such as high luminance, small étendue, and high color purity. By integrating a triple‐rod illumination system with a multi‐laser light source and an ultra‐wide‐angle projection system, the developed high‐efficiency optical system has achieved a brightness of 7000 lm and a throw ratio of 0.28 with an image size of 100–150 in. Another new technology, laser color processing (LCP), has offered vivid color reproduction which has a color gamut that is up to 180% wider than the BT.709 standard without appearing unnaturally colored. Furthermore, a speckle suppression effect produced by the multi‐laser light source has been demonstrated. In this paper, an overview of these newly developed technologies that are used in the novel laser‐light‐source projector is presented, and solutions to the issues of speckle noise and safety are presented.     

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.     

Perceptual Global Illumination Cancellation in Complex Projection Environments

The unintentional scattering of light between neighboring surfaces in complex projection environments increases the brightness and decreases the contrast, disrupting the appearance of the desired imagery. To achieve satisfactory projection results, the inverse problem of global illumination must be solved to cancel this secondary scattering. In this paper, we propose a global illumination cancellation method that minimizes the perceptual difference between the desired imagery and the actual total illumination in the resulting physical environment. Using Gauss‐Newton and active set methods, we design a fast solver for the bound constrained nonlinear least squares problem raised by the perceptual error metrics. Our solver is further accelerated with a CUDA implementation and multi‐resolution method to achieve 1–2 fps for problems with approximately 3000 variables. We demonstrate the global illumination cancellation algorithm with our multi‐projector system. Results show that our method preserves the color fidelity of the desired imagery significantly better than previous methods.     

Postural instability and motion sickness in a virtual moving room

OBJECTIVE: We examined motion sickness in an oscillating virtual environment presented via a video projector system. BACKGROUND: Visible oscillation of the physical environment is known to induce both postural instability and motion sickness, but it cannot be assumed that the same phenomena will occur in a virtual simulation of such motion. METHOD: Standing participants (3 men and 9 women, 20-22 years of age) were exposed to oscillation of a virtual room. The stimulus was a computer-generated simulation of a laboratory device that is known to induce postural instability and motion sickness. Participants viewed the simulation for up to 40 min and were instructed to discontinue if they experienced symptoms of motion sickness. RESULTS: Motion sickness incidence (42%) did not differ from that in studies using the corresponding physical moving room. Prior to motion sickness onset, the sick group exhibited changes in movement, relative to the well group, as predicted by the postural instability theory of motion sickness. Differences in movement between the sick and well groups developed over time, in contrast with previous studies using physical moving rooms, in which such movement differences have not evolved. CONCLUSION: The results indicate that changes in postural activity precede motion sickness that is induced by an oscillating virtual environment, but they also reveal differences in postural responses to virtual and physical motion environments. APPLICATION: Potential applications of this research include recommendations for the use of virtual environments as models for perception and action in physical environments.     

Multi‐viewer autostereoscopic display with dynamically addressable holographic backlight

Abstract— The Multi‐User 3‐D Television Display (MUTED), designed to provide three‐dimensional television (3‐D TV) by the display of autostereoscopic imagery to multiple viewers, each of whom should enjoy freedom of movement, is described. Such an autostereoscopic display system, which allows multiple viewers simultaneously by the use of head tracking, was previously demonstrated for TV applications in the ATTEST project. However, the requirement for a dynamically addressable, steerable backlight presented several problems for the illumination source. The MUTED system demonstrates significant advances in the realization of a multi‐user autostereoscopic display, partly due to the provision of a dynamic backlight employing a novel holographic laser projector. Such a technology provides significant advantages in terms of brightness, efficiency, laser speckle, and the ability to correct for optical aberrations compared to both imaging and scanned‐beam projection technologies.     

Integrating motion, illumination, and structure in video sequences with applications in illumination-invariant tracking

In this paper, we present a theory for combining the effects of motion, illumination, 3D structure, albedo, and camera parameters in a sequence of images obtained by a perspective camera. We show that the set of all Lambertian reflectance functions of a moving object, at any position, illuminated by arbitrarily distant light sources, lies "close" to a bilinear subspace consisting of nine illumination variables and six motion variables. This result implies that, given an arbitrary video sequence, it is possible to recover the 3D structure, motion, and illumination conditions simultaneously using the bilinear subspace formulation. The derivation builds upon existing work on linear subspace representations of reflectance by generalizing it to moving objects. Lighting can change slowly or suddenly, locally or globally, and can originate from a combination of point and extended sources. We experimentally compare the results of our theory with ground truth data and also provide results on real data by using video sequences of a 3D face and the entire human body with various combinations of motion and illumination directions. We also show results of our theory in estimating 3D motion and illumination model parameters from a video sequence     

Laser‐based multi‐user 3‐D display

Abstract— The development of a multi‐user stereoscopic display that does not require the use of special glasses (autostereoscopic), and that enables a large degree of freedom of viewer movement and requires only the minimum amount of information (a stereo pair) for the displays described. The optics comprise an RGB holographic laser projector that is controlled by the output of a multi‐target head‐position head tracker, an optical assembly that converts the projector output into steerable exit pupils, and a screen assembly comprising a single liquid‐crystal display (LCD) and image multiplexing screen. A stereo image pair is produced on the LCD by simultaneously displaying left and right images on alternate rows of pixels. Novel steering optics that replace the conventional backlight are used to direct viewing regions, referred to as exit pupils, to the appropriate viewers' eyes. The results obtained from the first version of the display, where the illumination source consists of several thousand white LEDs, are given and the current status of the latest prototype being constructed on the basis of these results is described. The work indicates that a laser‐based head‐tracking display can provide the basis for the next generation of 3‐D display.     

HD motion‐picture evaluation method for overdrive technology in the frequency domain

Abstract— In this paper, the development of an advanced level‐adaptive overdrive (A‐LAO) method applicable to a full‐HD LC projector with 1.84 Mpixels, which reduced the gray‐level response time to less than 16 msec, is introduced. In addition, it is shown that a response of less than 8 msec can be achieved by combining the A‐LAO method with a frame interpolation method (120‐Hz refresh). A new motion‐picture evaluation method using frequency‐domain analysis, in other words, perceived bandwidth instead of the conventional time‐domain‐analysis response time evaluation, is reported.     

Invited Paper: Blazed GxLP™ light modulators for laser projectors

Abstract— A GxL device is a one‐dimensional light modulator suitable for laser projectors. A blazed GxL, which diffracts the incident laser beam in only one direction was developed, and a contrast ratio of 10,000:1 and a diffraction efficiency of 70% was achieved by nanometer‐order control of ribbons based on the MEMS structural simulation and using common 0.25‐μm CMOS‐compatible fabrication processes. The 1.09‐in.‐long 1080‐pixel blazed GxL was implemented in the 2005‐in. Laser Dream Theater at the 2005 World Exposition in Aichi, Japan, and performed perfectly during that period. Recently, by optimizing the posts supporting the ribbon and flattening of the sacrificial layer using chemical mechanical polishing, an ultra high contrast ratio of 34,700:1 with a 0.72‐in.‐long GxL has been realized, and a smaller ceramic module with high reliability has also been realized. The blazed GxL will be a promising technology to further advance laser‐projector performance.     

Exploiting DLP Illumination Dithering for Reconstruction and Photography of High-Speed Scenes

In this work, we recover fast moving scenes by exploiting the high-speed illumination “dithering” of cheap and easily available digital light processing (DLP) projectors. We first show how to reverse-engineer the temporal dithering for off-the-shelf projectors, using a high-speed camera. DLP dithering can produce temporal patterns commonly used in active vision techniques. Since the dithering occurs at a very high frame-rate, such illumination-based methods can be “speed up” for fast scenes. We demonstrate this with three applications, each of which only requires a single slide to be displayed by the DLP projector. The quality of the result is determined by the camera frame-rate available to the user. Pairing a high-speed camera and a DLP projector, we demonstrate structured light reconstruction at 100 Hz. With the same camera and three or more DLP projectors, we show photometric stereo and demultiplexing applications at 300 Hz. Finally, with a real-time (60 Hz) or still camera, we show that DLP illumination acts as a very fast flash, allowing strobe photography of high-speed scenes. We discuss, in depth, some characteristics of the temporal dithering with a case study of a particular projector. Finally, we describe limitations, trade-offs and other issues relating to this work.     

High‐pixel‐rate grating‐light‐valve laser projector

Abstract— A high‐pixel‐rate, high‐contrast (30,000:1) wide‐color‐gamut grating‐light‐valve laser projector is reported. A new optical engine enabling high‐frame‐rate (240 Hz) scan projection is employed. Panoramic wide‐angle‐scan projection with a 64:9 aspect ratio was also developed. Speckle noise is eliminated using a simple but highly efficient technique. The optical throughput efficiency of the grating‐light‐valve laser projector is reviewed.     

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.     

Product Importance Sampling for Light Transport Path Guiding

The efficiency of Monte Carlo algorithms for light transport simulation is directly related to their ability to importance‐sample the product of the illumination and reflectance in the rendering equation. Since the optimal sampling strategy would require knowledge about the transport solution itself, importance sampling most often follows only one of the known factors – BRDF or an approximation of the incident illumination. To address this issue, we propose to represent the illumination and the reflectance factors by the Gaussian mixture model (GMM), which we fit by using a combination of weighted expectation maximization and non‐linear optimization methods. The GMM representation then allows us to obtain the resulting product distribution for importance sampling on‐the‐fly at each scene point. For its efficient evaluation and sampling we preform an up‐front adaptive decimation of both factor mixtures. In comparison to state‐of‐the‐art sampling methods, we show that our product importance sampling can lead to significantly better convergence in scenes with complex illumination and reflectance.