Stereoscopic depth perception survives significant interocular luminance differences

Abstract— The effects of interocular luminance differences on stereoscopic depth perception has been investigated. The stimuli were stereoscopic square‐shaped targets created from disparity embedded in a dynamic random‐dot stereogram, which eliminated other cues to depth perception. The results revealed that stereoscopic depth perception survived significant interocular differences in luminance levels, even up to differences of 60%, provided that display luminance was approximately 0.63 cd/m² or higher. In terms of design criteria, developers of stereo displays can use a fairly large range of interocular luminance levels and still induce good stereo depth perception.     

Subjective evaluation of visual fatigue due to misalignment of motion and still images in a stereoscopic display

Abstract— In this paper, the relative influences of misalignment such as cross‐talk, vertical shift, and motion blur on visual fatigue by using a binocular stereoscopic display has been verified. Experiments were conducted for two cases: a still image and a motion image. They were evaluated by using the simulator sickness questionnaire (SSQ). By changing the disparity angle, cross‐talk, and vertical shift in the still‐image experiment, it was found that the SSQ score of each parameter increased as the amount of each factor increased. With a two‐sample t‐test between the presence and absence of each factor, a significant difference was found for the case of a more than 36‐arcmin disparity, more than 20% cross‐talk, and more than 10% vertical shift. In the motion‐image experiment, in which motion speed and the misalignment were varied, it was found that movement of the disparity angle caused much more visual fatigue in comparison with the misalignment factors, which were cross‐talk and vertical shift. In contrast, motion images in addition to the cross‐talk and/or vertical shift had a slight but unnoticeable relationship to an increase in visual fatigue. Therefore, it was concluded that vertical shift dominated the evaluation for still images, and the movement itself dominated the evaluation for motion images. The results suggest that it is necessary to evaluate visual fatigue according to the representing case, still or motion images, of a 3‐D stereoscopic display.     

Review Paper: Human factors of stereo displays: An update

Abstract— This updated review paper provides a selected review of a number of important perceptual and human‐factors issues that arise when stereo displays are designed and used. This review and analysis draws heavily from the basic vision literature in order to help provide insight for future design solutions for stereo displays. Issues discussed include: (1) the basics of human stereopsis (horopter, binocular disparity, binocular rivalry); (2) low‐level factors (interocular cross talk, interocular differences in luminance and contrast, accommodation‐vergence mismatch, stereoanomaly); (3) contextual factors (spatio‐temporal frequency effects, distance scaling of disparity); and (4) a high‐level cognitive factor (high‐level cue conflict). In this updated review, significant new material has been added: (1) interocular luminance and contrast differences and their effect on stereo viewing; (2) more insightful discussion of accommodative‐vergence mismatch; (3) high‐level cognitive factor. Two topics in the earlier review (visual pathways; dark focus and dark vergence) have been deleted. The paper concludes with the presentation of several recommendations for the design of stereo displays.     

Changes in oculomotor functions before and after loading of a 3-D visually-guided task by using a head-mounted display

Changes in visual and oculomotor functions were tested in eight young volunteer subjects after performing a 3-D visually-guided task for 25min. The visual stimuli were given by using a head-mounted display. No significant change was detected in the AC/A ratio and the stereo-acuity. Changes were found in refraction and ocular convergence. Slight but significant hyperopic changes were detected in refraction after the task. The mean amplitude of convergence eye movement elicited by test Stimuli after the task was significantly changed in the pooled data. They were significantly reduced when the subjects were tested by the disparity step of 0.7°, but significantly increased when tested by the step of 6°. The mean amplitudes were not significantly changed after the task when the subjects were tested by the intermediate disparity steps of 1.5 and 3°. In data obtained for each subject, the amplitude of ocular convergence evoked by test stimuli after the task was reduced significantly in most subjects. In the majority of subjects, however, the results were not consistently significant when they were tested by step stimuli with different disparities. In only a few subjects, the changes were consistently significant except when the largest disparity was tested. On the other hand, the mean peak velocities of ocular convergence after the task were not significantly changed in the pooled data. In individual subjects, the changes of velocities of ocular convergence evoked by test stimuli after the task were more variable: they increased in some subjects but decreased in other subjects. Consequently, in only one subject, both amplitudes and peak velocities of ocular convergence tested by the-disparity steps of 0.7, 1.5 and 3° were consistently reduced after the task. The changes in refraction or ocular convergence found in this study were relatively small, and were not in the pathological range. The significance of these data are discussed. The results of the present study provide the basis for the more detailed analyses of the human factor in the head-mounted display.     

Influence of 3‐D cross‐talk on qualified viewing spaces in two‐ and multi‐view autostereoscopic displays

Abstract— To estimate the qualified viewing spaces for two‐ and multi‐view autostereoscopic displays, the relationship between image quality (image comfort, annoying ghost image, depth perception) and various pairings between 3‐D cross‐talk in the left and right views are studied subjectively using a two‐view autostereoscopic display and test charts for the left and right views with ghost images due to artificial 3‐D cross‐talk. The artificial 3‐D cross‐talk was tuned to simulate the view in the intermediate zone of the viewing spaces. It was shown that the stereoscopic images on a two‐view autostereoscopic display cause discomfort when they are observed by the eye in the intermediate zone between the viewing spaces. This is because the ghost image due to large 3‐D cross‐talk in the intermediate zone elicits different depth perception from the depth induced by the original images for the left and right views, so the observer's depth perception is confused. Image comfort is also shown to be better for multi‐views, especially the width of the viewing space, which is narrower than the interpupillary distance, where the parallax of the cross‐talking image is small.     

Fixation disparity: binocular vergence accuracy for a visual display at different positions relative to the eyes

Some observers do not fixate accurately at the point of regard: Their vergence angle (between the visual axes of the two eyes) may correspond to points slightly nearer or farther away. This vergence error, or fixation disparity, was measured with nonius (vernier) lines at six positions of a visual display relative to the eyes. At viewing distances of 40, 60, and 100 cm, the display was located either at eye level or at a downward inclination of gaze direction of -25 degrees relative to horizontal. Viewing conditions resembled typical office work. Lowering the screen induced a near shift in mean vergence response of 0.6 min arc, irrespective of viewing distance; the closer the screen, the more distant was the vergence response relative to the target (by 2.5 min arc on average). The slope of this proximity-fixation-disparity curve is an individual parameter of the vergence system. Actual or potential applications of this research include recommendations for the comfortable viewing distance of visual displays.     

The interaction of chromostereopsis and stereopsis in stereoscopic CRT displays

To give operators of high-speed, highly-manoeuvrable vehicles the ability to keep pace with their increasingly dynamic environment, stereoscopic 3-D displays may soon replace conventional 2-D displays. Important to the development of stereoscopic 3-D displays is the interaction of perceived depth created by hues (chromostereopsis) and perceived depth created by presenting different images of a single object to the left and right eye of the observer (stereopsis). The purpose of this research is to evaluate the interaction of chromostereopsis and stereopsis on a stereoscopic CRT by determining the level of accuracy with which subjects can properly interpret the relative depth differences of adjacent symbols containing six levels of hue and seven levels of stereoscopic disparity. This research demonstrated that hue, disparity, and the interaction of hue and disparity significantly influenced one's perception of depth on a stereoscopic monitor. The results suggest that caution should be exercised by the stereoscopic 3-D display format designer when choosing hues to represent images located in close proximity on a stereoscopic display. Due to the chromostereoscopic effect on the perception of depth, hues on extreme ends of the colour spectrum should not be used in situations where less than 3.39 arc minutes of disparity difference is being portrayed on a stereoscopic display, unless the hues are consistently being used to alter the depth presented by stereoscopic disparity, or the chromostereoscopic depth resulting from certain hues is consistently nullified by altering disparity levels accordingly.     

基于视差重映射的立体图像视觉舒适度提升

目的 针对人眼观看立体图像内容可能存在的视觉不舒适性,基于视差对立体图像视觉舒适度的影响,提出了一种结合全局线性和局部非线性视差重映射的立体图像视觉舒适度提升方法。方法 首先,考虑双目融合限制和视觉注意机制,分别结合空间频率和立体显著性因素提取立体图像的全局和局部视差统计特征,并利用支持向量回归构建客观的视觉舒适度预测模型作为控制视差重映射程度的约束;然后,通过构建的预测模型对输入的立体图像的视觉舒适性进行分析,就欠舒适的立体图像设计了一个两阶段的视差重映射策略,分别是视差范围的全局线性重映射和针对提取的潜在欠舒适区域内视差的局部非线性重映射;最后,根据重映射后的视差图绘制得到舒适度提升后的立体图像。结果 在IVY Lab立体图像舒适度测试库上的实验结果表明,相较于相关有代表性的视觉舒适度提升方法对于欠舒适立体图像的处理结果,所提出方法在保持整体场景立体感的同时,能更有效地提升立体图像的视觉舒适度。结论 所提出方法能够根据由不同的立体图像特征构建的视觉舒适度预测模型来自动实施全局线性和局部非线性视差重映射过程,达到既改善立体图像视觉舒适度、又尽量减少视差改变所导致的立体感削弱的目的,从而提升立体图像的整体3维体验。     

Binocular vision in a bi-ocular world: new-generation head-mounted displays avoid causing visual deficit

Our previous research highlighted adverse visual effects after wearing a binocular head-mounted display (HMD) for a 10 min stereoscopic visualization task. We have since proposed a theoretical, explanation based on the conflict between the depth. Such cues presented by image disparity and image focal depth. Such conflict, however, is not evident in all HMD configurations, and we replicated our early trials using a new-generation bi-ocular HMD produced by Virtuality Entertainment Ltd. Using similar, conventional optometric procedures with 50 participants, we observed no problems in the use of this display for immersion periods of to 30 min. This study demonstrates that effective HMDs can be produced through careful design and precision engineering. It also suggests a difference between the presentation of binocular and bi-ocular images and the requirements that they place on the visual system. Factors to consider in the future development of binocular displays are discussed.     

Using cross‐talk simulation to predict the performance of anaglyph 3‐D glasses

Abstract— The anaglyph 3‐D method is a widely used technique for presenting stereoscopic 3‐D images. Its primary advantage is that it will work on any full‐color display (LCDs, plasmas, and even prints) and only requires that the user view the anaglyph image using a pair of anaglyph 3‐D glasses with usually one lens tinted red and the other lens tinted cyan (blue plus green). A common image‐quality problem of anaglyph 3‐D images is high levels of cross‐talk — the incomplete isolation of the left and right image channels such that each eye sees a “ghost” of the opposite perspective view. An anaglyph cross‐talk simulation model has been developed which allows the amount of anaglyph cross‐talk to be estimated based on the spectral characteristics of the anaglyph glasses and the display. The model is validated using a visual cross‐talk ranking test which indicates good agreement. The model is then used to consider two scenarios for the reduction of cross‐talk in anaglyph systems and finds that a considerable reduction is likely to be achieved by using spectrally pure displays. The study also finds that the 3‐D performance of commercial anaglyph glasses can be significantly better than handmade anaglyph glasses.     

Angular dependence of the performance of stereoscopic liquid‐crystal‐display (LCD) television using shutter glasses (SG)

Abstract— 3‐D cross‐talk typically represents the ratio of image overlap between the left and right views. For stereoscopic LCDs using shutter‐glasses technology, 3‐D cross‐talk for stereoscopic LCD TV with a diagonal size of 46 in. and vertical alignment (VA) mode was measured to change from 1% to 10% when the stereoscopic display is rotated around the vertical axis. Input signals consist of the left and right images that include patterns of different amounts of binocular disparity and various gray levels. Ghost‐like artifacts are observed. Furthermore, intensities of these artifacts are observed to change as the stereoscopic display is rotated about the vertical axis. The temporal luminance of the LCD used in stereoscopic TV was found to be dependent on the viewing direction and can be considered as one cause of the phenomenon of angular dependence of performance for stereoscopic displays.     

Human fusion range for polarized 3D display

If discrepancy between accommodation and convergence caused by a stereoscopic display exceeds fusion range of human eyes, viewers will see ghosting image, which leads to the loss of correct depth information and even causes severe visual fatigue. In this paper, an experiment aiming to investigate the binocular fusion range is conducted for a polarized 3D display. Two experimental trials are arranged to examine two aspects of fusion range including outward depth and inward depth. 3D modeling software is used to generate the test stereoscopic image pairs, which vary in depth by adjusting the separation between the virtual cameras. Angular parallax corresponding to the limit of fusion range is obtained by determining critical point of ghosting images. The experimental results show deviation between theoretical fusion range calculated by formula and experimental one.?0.223° to 0.275° represent critical fusion range for the polarized 3D display to avoid ghosting images.     

Electronic paper display preferred viewing distance and character size for different age groups

This study explores the preferred viewing distance and character size for an electronic paper display for three age groups. Proofreading speed and accuracy ratio were measured during Chinese proofreading tests using the preferred character size and minimum acceptable character size. Data analysis showed that the mean preferred viewing distance for young, middle-aged and older groups was 503, 455 and 444 mm, respectively. The mean preferred character size determined by young, middle-aged and older groups was 42.0, 50.0 and 55.2 min arc, respectively. The proofreading test results indicated that the older group proofread significantly more slowly (1.25 word/sec) than the young (1.76 word/sec) and middle-aged groups (1.74 word/sec). Further, the participants proofread more correctly with their preferred character size (73.3%) than with their minimum acceptable character size (65.4%). This study provides valuable information for the design of Chinese text presentations for various age groups. STATEMENT OF RELEVANCE: This study confirmed the preferred viewing distance and character size for E-paper display were influenced by age. The preferred Chinese character size for young, middle-aged and older people was 42, 50 and 55 min arc, respectively. Therefore, the age factor should be considered for E-paper displays design and video display terminal (VDT) guidelines.     

结合立体视觉舒适度的立体图像显著性检测

针对先前的立体图像显著性检测模型未充分考虑立体视觉舒适度和视差图分布特征对显著区域检测的影响,提出了一种结合立体视觉舒适度因子的显著性计算模型.该模型在彩色图像显著性提取中,首先利用SLIC算法对输入图像进行超像素分割,随后进行颜色相似区域合并后再进行二维图像显著性计算;在深度显著性计算中,首先对视差图进行预处理;然后基于区域对比度进行显著性计算;最后,结合立体视觉舒适度因子对二维显著图和深度显著图进行融合,得到立体图像显著图.在不同类型立体图像上的实验结果表明,该模型获得了85%的准确率和78%的召回率,优于现有常用的显著性检测模型,并与人眼立体视觉注意力机制保持良好的一致性.     

Visual comfort enhancement study based on visual attention detection for stereoscopic displays

Although numerous potential causes may lead to visual discomfort when viewing content on three‐dimensional (3D) displays, vergence–accommodation conflict is a particular cause of binocular parallax‐based stereoscopic displays, and it is unavoidable. Based on the study of 3D content visual attention, we proposed a novel stereoscopic depth adjustment method to improve the visual comfort and enhance perceived naturalness. The proposed method combined the 3D image saliency and specific viewing condition to establish a novel model for computing the optimum zero‐disparity plane of stereoscopic image. The results of perception experiments, focused on visual comfort and stereoscopic sensation, supported that the proposed method can significantly enhance stereoscopic viewing comfort and even can improve the stereoscopic sensation by insuring the 3D image fusion.     

Disparity-based just-noticeable-difference model for perceptual stereoscopic video coding using depth of focus blur effect

Human 3D perception provides an important clue to the removal of redundancy in stereoscopic 3D (S3D) videos. Because objects outside the binocular fusion limit cannot be fused on retina, the human visual system (HVS) makes them blur according to the depth-of-focus (DOF) effect to increase the binocular fusion limit and suppress diplopia, i.e. double vision. Based on human depth perception, we propose a disparity-based just-noticeable-difference model (DJND) to save bit-rate and improve visual comfort in S3D videos. We combine the DOF blur effect with conventional JND models in the pixel domain into DJND. Firstly, we use disparity information to get the average disparity value of each block. Then, we integrate the DOF blur effect into luminance JND (LJND) by a selective low pass Gaussian filter to minimize the visual stimulus in S3D videos. Finally, we incorporate disparity information into the filtered JND models to obtain DJND. Experimental results demonstrate that the proposed method successfully improves both image quality and visual comfort in viewing S3D videos without increasing the bit-rate.     

Electronic paper display preferred viewing distance and character size for different age groups

This study explores the preferred viewing distance and character size for an electronic paper display for three age groups. Proofreading speed and accuracy ratio were measured during Chinese proofreading tests using the preferred character size and minimum acceptable character size. Data analysis showed that the mean preferred viewing distance for young, middle-aged and older groups was 503, 455 and 444 mm, respectively. The mean preferred character size determined by young, middle-aged and older groups was 42.0, 50.0 and 55.2 min arc, respectively. The proofreading test results indicated that the older group proofread significantly more slowly (1.25word/sec) than the young (1.76 word/sec) and middle-aged groups (1.74 word/sec). Further, the participants proofread more correctly with their preferred character size (73.3%) than with their minimum acceptable character size (65.4%). This study provides valuable information for the design of Chinese text presentations for various agegroups.

Statement of Relevance: This study confirmed the preferred viewing distance and character size for E-paper display were influenced by age. The preferred Chinese character size for young, middle-aged and older people was 42, 50 and 55 min arc, respectively. Therefore, the age factor should be considered for E-paper displays design and video display terminal (VDT) guidelines.     

Visibility of transmissive liquid crystal displays under dynamic lighting conditions.

Liquid crystal displays maintain superior contrast under bright sunlight conditions compared with cathode-ray tube displays. This attribute, along with reduced weight, volume, and power requirements, make liquid crystal displays especially desirable for use in vehicular applications. The present experiment was designed to determine the luminance requirements for transmissive liquid crystal displays viewed under a wide range of lighting conditions typical of many vehicular environments. Both the ambient illumination incident on the display surface and the forward-field-of-view adaptation luminance were parametrically manipulated. The visual task involved speeded spatial discrimination responses for detection of the gap in a modified Landolt-C acuity target. The results indicate that under the worst lighting conditions tested, a display luminance of approximately 180 cd/m2 yielded asymptotic spatial discrimination performance. The results have been incorporated into a predictive visual performance model for spatial discrimination tasks, which describes the present data well and represents a first step toward a device-independent model of display visibility.     

Cross‐talk acceptability in natural still images for different (auto)stereoscopic display technologies

Abstract— One of the most annoying distortions in (auto)stereoscopic displays is probably cross‐talk, visible as double edges, which is mainly caused by an imperfect separation of left‐ and right‐eye images. For different types of three‐dimensional (3‐D) displays, cross‐talk is caused by different origins, which could result in different levels of perceived image distortion. To evaluate the influence of (auto)stereoscopic display technology on cross‐talk perception, optical measurements and subjective assessments were performed with three different types of 3‐D displays. It is shown with natural still images that the 3‐D display technology with the lowest luminance and contrast level tolerates the highest level of cross‐talk, while still maintaining an acceptable image‐quality level.     

Eye movements and visual discomfort when viewing stereoscopic 3D content

The visual brain fuses the left and right images projected onto the two eyes from a stereoscopic 3D (S3D) display, perceives parallax, and rebuilds a sense of depth. In this process, the eyes adjust vergence and accommodation to adapt to the depths and parallax of the points they gazed at. Conflicts between accommodation and vergence when viewing S3D content potentially lead to visual discomfort. A variety of approaches have been taken towards understanding the perceptual bases of discomfort felt when viewing S3D, including extreme disparities or disparity gradients, negative disparities, dichoptic presentations, and so on. However less effort has been applied towards understanding the role of eye movements as they relate to visual discomfort when viewing S3D. To study eye movements in the context of S3D viewing discomfort, a Shifted-S3D-Image-Database (SSID) is constructed using 11 original nature scene S3D images and their 6 shifted versions. We conducted eye-tracking experiments on humans viewing S3D images in SSID while simultaneously collecting their judgments of experienced visual discomfort. From the collected eye-tracking data, regions of interest (ROIs) were extracted by kernel density estimation using the fixation data, and an empirical formula fitted between the disparities of salient objects marked by the ROIs and the mean opinion scores (MOS). Finally, eye-tracking data was used to analyze the eye movement characteristics related to S3D image quality. Fifteen eye movement features were extracted, and a visual discomfort predication model learned using a support vector regressor (SVR). By analyzing the correlations between features and MOS, we conclude that angular disparity features have a strong correlation with human judgments of discomfort.