An eye behavior measuring device for VR system

This work presents an eye-tracking and pupil size-measuring device that interfaces with a computer for applications useful in psychometry, ophthalmology, physiology and virtual reality (VR) systems. This system utilizes a change-coupled device (CCD) camera, appropriate lenses, PC with frame grabber and a DSP unit with various types of VR equipment, i.e., HMD, simulator or LCD projection device. The digital signal processing unit is used to calculate the average brightness and contrast of the VR video image. A CCD camera with various attachments can be mounted on various VR systems to capture the human eye image for testing. An image capture card and a personal computer are used to analyze the test image. From the eye digital image, the computer obtains data on the pupil size and a trace of the tested eye. A pattern recognition computer program and five measurement parameters are used to distinguish the position of the pupil, calculate the pupil location coordinate and analyze the physical conditions of the user. These data can be plotted against the average brightness and contrast of the VR video image in real time. This information is shown on the screen of a personal computer and used for cross-link analysis. This eye-tracking interface can determine the position of a subject's pupil and map that position into a display point on a computer screen. The pupil size and location data versus the average brightness and contrast of a VR video image are computed in real time.     

眼模型下的投影式头盔物镜设计及视空间评价

进一步完善了投影式头盔系统的视空间评价方法,应用接近实际情况的眼模型来模拟人眼对头盔物镜系统进行评价。由视空间的评价结果出发,从眼模型的成像效果反过来进一步指导头盔系统的设计工作。设计结果显示,轴上视场和大视场的调制传递函数特性良好,在轴上视场可以达到1′的人眼最小分辨角,在大视场可以达到微显示器单个像素确定的视锐度,表明此系统在视空间的分辨力满足实际使用需要。系统最大畸变小于5%,色差不会对人眼分辨产生影响。     

基于视网膜投影显示的头盔显示器设计

传统的透射型头盔显示器虽然可以显示虚拟图像,但当眼睛调节焦距时无法清晰显示虚拟图像,研究一种新型的透射型头盔显示技术,其特点是既可以看到外部景物,也可以同时看到微型显示芯片上所显示的虚拟图像,并且虚拟图像独立于人眼的调节。介绍显示技术的原理,用光学设计软件Zemax完成整体光学系统设计,优化后系统达到衍射极限,滤波投影系统中MTF在60 lp/mm处达到了0.7;用Autocad软件设计了头盔显示器结构。光路成像实验结果表明:设计的系统可以看到外界图像和虚拟图像,当眼睛对外界景物聚焦时,外界景物与虚拟图像都保持清晰,眼睛对外界景物离焦时,外界景物变得模糊而虚拟图像仍然保持清晰。     

数字电视的光色计量及其装置

结合市面上常见数字电视器件CRT,LCD,PDP等的显示原理及特性，具体讲解光色计量指标测量方法及原理，系统量值传递是通过国家色度和亮度基准标准灯来完成的。利用虚拟仪器技术建立的数据采集及分析系统，可对待测仪器的参数进行实时数据检测和数据分析。整个测试系统亮度和色坐标不确定度小于2%和0.005. 通过对市场主流电视产品的集中检测，将其相对光谱功率分布、亮度、色坐标、亮度不均匀性及对比度等综合参数进行对比，给出了测试结果及各种电视性能分析，为数字彩色电视计量工作提供了参考。     

Understanding the exposure-time effect on speckle contrast measurements for laser displays

To evaluate the influence of exposure time on speckle noise for laser displays, speckle contrast measurement method was developed observable at a human eye response time using a high-sensitivity camera which has a signal multiplying function. The nonlinearity of camera light sensitivity was calibrated to measure accurate speckle contrasts, and the measuring lower limit noise of speckle contrast was improved by applying spatial-frequency low pass filter to the captured images. Three commercially available laser displays were measured over a wide range of exposure times from tens of milliseconds to several seconds without adjusting the brightness of laser displays. The speckle contrast of raster-scanned mobile projector without any speckle-reduction device was nearly constant over various exposure times. On the contrary to this, in full-frame projection type laser displays equipped with a temporally-averaging speckle-reduction device, some of their speckle contrasts close to the lower limits noise were slightly increased at the shorter exposure time due to the noise. As a result, the exposure-time effect of speckle contrast could not be observed in our measurements, although it is more reasonable to think that the speckle contrasts of laser displays, which are equipped with the temporally-averaging speckle-reduction device, are dependent on the exposure time. This discrepancy may be attributed to the underestimation of temporal averaging factor. We expected that this method is useful for evaluating various laser displays and clarify the relationship between the speckle noise and the exposure time for a further verification of speckle reduction.     

Reduced order modeling of head related impulse responses for virtual acoustic displays

This study investigated the use of reduced order head related impulse response (HRIR) models to improve the computational efficiency in acoustic virtual displays. State space models of varying order were generated from zero-elevation HRIRs using a singular value decomposition technique. A source identification experiment was conducted under anechoic conditions in which three subjects were required to localize sounds in the front horizontal plane. The sounds were either (1) real sources (emitted by individual loudspeakers in a semi-circular array), (2) virtual sources generated from the original HRIRs, or (3) virtual sources generated using reduced order state space models. All virtual sources were created by simultaneous activation of two loudspeakers at +/- 30 degrees using a virtual source imaging technique based on either the measured or modeled HRIRs. The errors in the perceived direction of the virtual sources generated from the reduced order models were compared to errors in localization using the original HRIRs. The results demonstrate that a very significant reduction in model size can be achieved without significantly affecting the fidelity of the virtual display of horizontally placed sources.     

Configuration of virtual cameras for ground based 360° three-dimensional display

Most technologies provide three-dimensional (3D) display in the front of screens which are in parallel with the walls, and the sense of immersion is decreased. To get the right ground based 3D imaging, cameras’ imaging planes should be parallel to the public focus plane, and the cameras’ optical axes should be shifted to the center of the public focus plane in both vertical and horizontal directions. Virtual cameras are used to display 3D model in computer system. Two virtually capturing methods for ground based 3D display are presented. The position of virtual camera is determined by the observer's eye positions in the real world. When the observer stands in the displayed circumcircle on the ground, off-axis perspective projection virtual cameras are used. If the observer stands out the circumcircle, offset perspective projection virtual cameras and the orthogonal projection virtual cameras are adopted. An experimental system for ground based 360° 3D display is demonstrated for viewing horizontally, which provides high-immersion 3D visualization. The displayed heights are compared with the measured results.     

B-scanning and holography in ophthalmic diagnosis

The ultrasonic holographic apparatus now undergoing evaluation at Moorfields Eye Hospital and described in the last issue is capable of obtaining A-scan, B-scan and holographic displays of the living human eye. The clinical application of the machine is described and some early results presented. These emphasize the complementary nature of B-scan and holographic displays and are used to discuss the extent to which holography may be a valuable diagnostic technique in ophthalmology.     

Efficiency balance of a light guide plate with microstructures for a see-through head-mounted display

The efficiency balance phenomenon for see-through head-mounted displays with different microstructure conditions can be found both theoretically and using optical simulation software.A simple mathematical calculation is used to determine the relationship between the real image(see-through function) energy and the virtual image energy.The simulation is based on factors taken from previous research studies.It is found that the balance value of the optical efficiency remains almost constant(66.63% to 67.38%) under different microstructure conditions.In addition,suitable conditions for the microstructures in see-through head-mounted displays for daily applications can be predicted.     

远距离成像汽车平视显示光路结构设计

针对汽车AR-HUD显示虚像视距更远、虚像视场角更大的需求,采用自由曲面离轴反射光路结构,设计了一种焦距为-309 mm,虚像视距为7.5 m,虚像视场角为9.8°×5.5°的虚像显示光路。为保证驾驶员观察到的虚像的清晰度,结合人眼典型分辨角为1′,源图像显示模块采用分辨率为854×480 pixel的背投式DLP微投影系统。将人眼与虚像显示光路作为整体进行设计,使用Eyebox(孔径光阑偏移范围)模拟驾驶员眼睛活动范围,对于不同的孔径光阑位置,该光学系统的虚像面在奈奎斯特空间频率0.33 lp/mm处,中心视场MTF值大于0.6,全视场MTF值大于0.3。此外,使用蒙特卡罗方法对该系统取不同入瞳位置时进行了初步公差分析,系统90%的MTF值大于0.49,表明该系统容差能力较强。     

头盔显示器在视空间性能评价中的眼睛转动问题研究

以一款由Erfle目镜为目视系统的头盔显示器为例,给出了眼睛转动时其视空间的性能评价方法、计算公式和评价结果.评价内容包括MTF、调节、像散、横向色差和畸变.对眼睛转动和不转动情况下的结果进行了分析比较：由于转动,使得某些视场的MTF 、调节等性能指标严重变差,成清晰像的范围明显减小;系统的性能出现了明显的非对称性.结果表明:无法根据眼睛不转动情况下的系统性能来判断转动情况下的性能,而只能通过实际的光线追迹才能获得.     

平面三维显示技术的研究现状

平面三维显示技术是近年来最新出现的虚拟现实显示技术,其最大的特点是观察者无需使用任何辅助附加设备,直接用肉眼就可看到屏幕上显示的三维图像。为推进三维显示技术的发展,进一步研究了视差立体成像原理,并据此介绍几种平面三维显示方法及其工作原理,包括障栅立体显示、微柱透镜阵列立体显示、偏振片立体显示和基于微柱透镜立体显示原理的多视点系统,阐述并分析了系统的优缺点。以日本三洋公司的四视角立体显示装置、南京大学的多视点三维显示系统和NEC液晶科技的HDDP三维显示系统为例,描述了国内外该项技术近期的研究现状,分析了存在的技术难点,展望了该应用领域的发展前景。     

Wearable optical see-through head-mounted display capable of adjusting virtual image depth

Accommodation and convergence play critical roles in the natural process of depth perception, and the field of natural three-dimensional （3D） perception in stereo displays has been extensively explored. However, no prototypes of these natural 3D displays are suitable for wear due to the system size and weight. In addition, few of the researches have involved subjects with ametropia. We propose and develop an optical see-through head-mounted display （HMD） capable of diopter adjustment of both the virtual image and the real world scene. The prototype demonstrates a diagonal field of view （NOV） of 42° and an exit pupil diameter of 9 mnl, and a diopter adjustment range of -5.5D to 0D. Depth adjustment of virtual image is demonstrated with experiments, the results show the HMD can be further used to investigate the accommodation and convergence cues in depth perception in AR environment, particularly for users with different degree of the ametropia.     

Active localization of virtual sounds

A simple virtual sound display built around a microcomputer and analog hardware is described. The display implements most of the primary cues for sound localization in the ear-level plane. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, it is concluded that simple displays like the one described are effective in creating the impression of external sounds to which observers can locomote with ease; in particular, this means that simulation of the direction-dependent spectral shaping effects of the pinnae is not a necessary requirement for extracranial sound localization.     

Stereoscopic Full-Color Light Emitting Diode Display Using Parallax Barrier for Different Interpupillary Distances

The viewing areas of stereoscopic full-color light emitting diode (LED) displays using parallax barriers are investigated for viewing by observers with different interpupillary distances. We have developed stereoscopic full-color LED displays using three types of parallax barriers for different interpupillary distances. Experiments on distance perception of stereoscopic targets have been conducted with the stereoscopic LED displays using parallax barriers, as well as a stereoscopic LED display using polarizing eyewear. It was shown that enlargement of the viewing area allows several viewers with different interpupillary distances to view a stereoscopic image. It is suggested that parallax barriers designed for narrower interpupillary distances than the viewer’s own provide a viewer with stereoscopic perception.     

Watt-level red-emitting diode lasers and modules for display applications

Red-emitting lasers for display applications require high output powers and a high visibility. We demonstrate diode lasers and modules in the red spectral range based on AlGaInP with optical output powers up to 1 W and a nearly diffraction limited beam. These high-luminance light sources based on tapered lasers are well suited for laser TVs and projectors for virtual reality simulators based on the flying spot technology. Additionally, we developed diode lasers with internal distributed Bragg reflector (DBR) surface gratings. These DBR tapered lasers and master-oscillator power-amplifiers based on DBR ridge-waveguide lasers and tapered amplifiers feature high power, single mode emission with coherence lengths up to several meters, which are suitable for the next-generation 3D displays based on holography.     

45°视场角投影式头盔在视空间的性能评价

提出理想透镜像距不变,通过改变其焦距来模拟人眼调节完成视空间性能评价的一种新方法.对45°投影式头盔物镜系统进行了精确的视空间评价.其MTF评价结果显示,系统在眼睛注视0°视场时可达到1 arc minute的分辨率;注视＋13.1°视场时可达到1.4 arc minute的分辨率.眼睛无论是注视0°视场还是＋13.1°视场,只有在一定的视场范围内,调节模糊和像散模糊才不会影响图像的清晰程度,且系统的横向色差和二级光谱均小于人眼的最小分辨角,不会对成像清晰度造成影响.眼睛注视＋13.1°视场时,系统的调节和调节模糊、像散和像散模糊、横向色差和二级光谱均具有明显的非对称性.此外,与改变理想透镜像距进行视空间评价的结果相比较,只有注视13.1°视场时的MTF差别较大.     

Eye models for the prediction of contrast vision in patients with new intraocular lens designs

Theoretical calculations of the polychromatic modulation transfer function (MTF) and wave-front aberration were performed with physiological eye models. These eye models have an amount of spherical aberration that is representative of a normal population of pseudophakic eyes implanted with two different types of intraocular lens (IOL) made from high-refractive-index silicone. These theoretical calculations were compared with the measured contrast sensitivity function (CSF) under mesopic lighting conditions and with wave-front aberration (obtained with a Hartmann-Shack wave-front sensor) collected from 37 patients bilaterally implanted with the same types of lens. The relationships between the ocular wave-front aberration and the MTF predicted by the eye models and the CSF and the ocular wave-front aberration measured in eyes implanted with IOLs were investigated. The predicted improvements in MTF and wave-front aberration correlated well with the improvements measured in practice. Physiological eye models are therefore useful tools for IOL design.     

An ophthalmic ultrasound scanning system

An ultrasonic compound scanning system has been developed specifically for ophthalmology. Clinical application and facility of operation are important criteria in its design. A hand-operated scanning mechanism and special circuitry are used to attain the high-resolution displays needed in ultrasonic investigations of the eye region. Accessible controls are provided for clinically relevant functions. Potentially troublesome operational tasks are performed internally by the system.     

投影式头盔物镜设计在视空间的性能评价

对一款折衍混合投影式头盔(Head-mounted projective displays,HMPDs)物镜进行了精确的视空间评价,并给出了详细的评价步骤和评价结果。在对调制传递函数(MTF)进行评价时,充分考虑了人眼的焦距和瞳孔对评价结果的影响,给出了调节和像散所造成的分辨力损失的计算公式。评价结果显示:对于3 mm瞳孔,该系统中心视场调制传递函数在0.5 cycles/(′)达到了0.55,达到了人眼的最小分辨角(1′)。当眼睛注视投影像面中心时,轴外点最大需要0.35D的调节量,由此造成的分辨力损失最大为3.5′。由于像散造成的分辨力损失最大只有1.1′。横向色差和二级光谱最大值分别只有0.57′和0.17′,均小于人眼的最小分辨角。这些结果证明此设计满足投影式头盔物镜的使用需要。该方法适用于所有的头盔系统在视空间的性能评价。