Visual comfort in autostereoscopic display

Autostereoscopic displays are likely to become widely used products in the future. However, certain physiological factors, especially visual comfort, limit their development. In this study, four observational parameters – ambient illuminance, image content, scaling ratio, and horizontal distance between major and minor objects – were evaluated to determine the degree of visual comfort offered by 3D computer‐generated images on an autostereoscopic display. Visual comfort score with the range of 0–1 is designed to represent the degree of visual comfort for the 3D images with different manipulations of ambient illuminance, image content, scaling ratio, and horizontal distance between major and minor objects in this study. Subjects were asked to indicate images that produced discomfort. The proportion of images for each condition where participants indicated that viewing the image was comfortable was computed. Images receiving a proportion of 0.5 or greater were classified as acceptable. The disparity ranges over which acceptable images were attained for each participant and for each condition were analyzed with analysis of variance. The analytical results indicate that ambient illuminance and image content have a significant effect on the acceptable disparity range, while scaling ratio and horizontal distance between major and minor objects did not.     

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。     

Visual comfort enhancement in stereoscopic 3D images using saliency-adaptive nonlinear disparity mapping

Perceptually salient regions have a significant effect on visual comfort in stereoscopic 3D (S3D) images. The conventional method of obtaining saliency maps is linear combination, which often weakens the saliency influence and distorts the original disparity range significantly. In this paper, we propose visual comfort enhancement in S3D images using saliency-adaptive nonlinear disparity mapping. First, we obtain saliency-adaptive disparity maps with visual sensitivity to maintain the disparity-based saliency influence. Then, we perform nonlinear disparity mapping based on a sigmoid function to minimize disparity distortions. Finally, we generate visually comfortable S3D images based on depth-image-based-rendering (DIBR). Experimental results demonstrate that the proposed method successfully improves visual comfort in S3D images by producing comfortable S3D images with high mean opinion score (MOS) while keeping the overall viewing image quality.     

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.     

Luminance effects influencing perception of 3‐D TV imagery

Abstract— This study investigates whether screen luminance or ambient illumination has a significant effect on the perception of 3‐D TV imagery for static images and dynamic films. Two types of stimuli were shown on a multi‐view stereoscopic display: the static image, which included computer‐generated and photographic images, and dynamic film, which contained real‐life and animation images. In each treatment with a different level of screen luminance, subjects completed psychophysical and physiological measurements and subjective comfort evaluations. The results showed that when subjects viewed 3‐D static images, the ambient illumination affected psychophysical visual fatigue and screen luminance had a significant effect on subjective comfort evaluation and visual discrimination performance. However, when subjects viewed 3‐D dynamic films, screen luminance was the major factor causing psychophysical visual fatigue, and ambient illumination significantly affected subjective comfort evaluation. The outcomes contribute to knowledge concerning the suitable viewing conditions for the 3‐D viewing experience. Future work will explore the intolerance threshold of the lowest display luminance or the effect of decomposition of the screen on other physiological measurements.     

DP3 signal as a neuro-indictor for attentional processing of stereoscopic contents in varied depths within the ‘comfort zone’

When viewing stereoscopic 3D (S3D) displays, excessive binocular disparity is one of the major sources for the induced visual fatigue. Limiting the disparity within a certain range termed ‘comfort zone’ is a useful approach to alleviate the negative impact of viewing the S3D displays. Using the event-related potential (ERP) approach, we have previously showed that the differential P3 (DP3) signal evoked in an oddball task could be a useful neural indicator of the involvement of high-level cognitive functions in viewing S3D contents within the comfort zone compared to viewing 2D contents, despite of the similar subjective comfort of viewing experience for the two display conditions. It remains unclear whether the DP3 signal is sensitive enough for examination of the high-level processing when viewing S3D contents in different disparities within the comfort zone. Here, the DP3 signals were recorded while subjects performed an oddball task presented in S3D modality for three disparities (0.15, 0.45 and 0.76 arcdeg) within the comfort zone. Whereas the oddball task was of similar comfort by subjective measurement for different disparities, the DP3 signal showed monotonic delay in latency for increasing disparity, suggesting the capability of the DP3 signal for establishing a ‘cognitive comfort zone’ in terms of the high-level cognitive functions.     

3D visual comfort assessment by measuring the vertical disparity tolerance

Misalignment in stereo images leads to 3D discomfort, but the visual tolerance for disparities varies with viewing environment and stimulus. The aim of the study was twofold: first, to assess if vertical disparity tolerance (VDT) could be a reliable indicator of 3D visual comfort under certain restrained condition when vertical disparity is induced; second, to be able to predict how viewing conditions can affect visual comfort using an analytical model. Two viewing condition parameters were considered: luminance and stimulus angular size. The study was carried out in two experiments involving 17 subjects. In Experiment 1, visual comfort and vertical disparity tolerance were measured by a series of psychophysical tests for different stimulus angular sizes and luminance. Based on a regression analysis of this data, a model was proposed to estimate VDT as a function of luminance and stimulus angular size. In Experiment 2, a validation test was carried out to assess the quality of the model. Results confirm that for given viewing conditions (luminance, angular size, induced vertical disparity), the visual comfort measured is in agreement with the one predicted (ρ = 1.0008, p = 0.0026). VDT is a recognized reliable indicator of visual comfort due to vertical disparity and the model can be used to predict visual comfort for given viewing conditions.     

Effects of bending curvature and text/background color-combinations of e-paper on subjects’ visual performance and subjective preferences under various ambient illuminance conditions

The study used the simulated e-paper to investigate how the bending radius of curvature (−10 cm, plane, and 10 cm) and 12 text/background color-combinations of e-paper affect subjects’ visual performance and subjective preference under various ambient illuminance conditions (200 and 500 lx). Analysis results indicated that the bending curvature and ambient illuminance did not significantly affect subjects’ visual performance. However, subjects visual performance differed significantly for different text/background color combinations of the simulated e-paper. When the background color of the simulated e-paper was set to yellow-like condition and the luminance of the text was low (2.2 and 4.6 cd/m²), subjects’ visual performance was best. Regarding the subjective preferences of subjects, the results of this research also demonstrated that the bending curvature, text/background color combinations and ambient illuminance all significantly affected the subjective preferences of subjects. Subjects exhibited the best preference under the following settings: bending curvature of the simulated e-paper set to plane; background color of the simulated e-paper set to yellow-like condition and low text luminance (2.2 or 4.6 cd/m²); high ambient illuminance (500 lx).     

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.     

Psychophysical research on switching between light emitting and reflecting modes of light adaptable display considering equal visibility

Viewing high-luminance displays such as liquid crystal displays or organic light emitting diode displays under low-light conditions causes an unbearable glare, while viewing them with low luminance under bright-light conditions reduces visibility. Recently, several research groups have reported light adaptable displays (LADs) to extend display visibility over a wide range of light conditions. Here, we present a psychophysical study on how to effectively utilize the LAD using two different display types for the first time. LAD features two switchable display types: light emitting mode (LEM) and light reflecting mode (LRM). To maintain visibility and prevent visual artifacts, we investigate when to switch modes between LEM and LRM. We conduct psychophysical experiments involving seventy subjects. They are asked to select illuminance levels under which they perceive that the LEM and LRM look the same depending on luminance of the LEM. We propose a mode-switching condition by combining our previous results on the comfortable luminance of LEM display according to the ambient illuminance and the selected illuminance results providing equal visibility of both LEM and LRM displays.     

Effect of disparity and viewing ambient illumination on stereoscopic viewing: An eye movement approach

Researchers have found that factors related to viewing content and viewing environment could influence viewers' stereoscopic viewing experiences. In this paper, the effect of both disparity and viewing ambient illumination condition on stereoscopic viewing was investigated by using an eye movement approach. The eye movement responses to random dot stereograms (RDS) stimuli in stereoscopic viewing were studied by performing a fusion range measurement experiment involving a judgment task. The fusion ranges under two ambient illumination conditions, eye movement responses to RDS stimuli and effects of disparity on eye movement parameters, were analyzed, respectively. The experimental results showed that fusion range under two ambient illumination conditions were different, and changes of eye movement parameters were different among various disparities when ambient illumination conditions varied. As a result, in order to improve viewers' viewing experiences when viewing different 3D contents, the arrangement of viewing ambient illumination conditions and the selection of disparity should be appropriately considered. The findings in this paper provide guidelines to reasonably arrange the viewing ambient illumination condition and efficiently produce healthy disparity in stereoscopic viewing.     

Visual discomfort relaxation for stereoscopic 3D images by adjusting zero-disparity plane for projection

It is a challenging task to improve the visual comfort of a stereoscopic 3D (S3D) image with satisfactory viewing experience. In this paper, we propose a visual comfort improvement scheme by adjusting zero-disparity plane (ZDP) for projection. The degree of visual discomfort is predicted by considering three factors: spatial frequency, disparity response, and visual attention. Then, the selection of an optimal ZDP is guided by the predicted visual discomfort map. Finally, the disparity ranges of the crossed and uncrossed disparities are automatically adjusted according to the ZDP as requirements. Experiment results show that the proposed scheme is effective in improving visual comfort while preserving the unchanged depth sensation.     

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.     

Exploring crosstalk perception for stereoscopic 3D head‐up displays in a crosstalk simulator

In today's upper class vehicles, head‐up displays (HUDs) are state of the art human–machine interfaces used to increase driving security and comfort. Working with a stereoscopically perceived viewing impression, a novel automotive 3D HUD would allow the simultaneous visualization of multiple contents in various depth planes. However, stereoscopic crosstalk is one of the most important parameters influencing the image quality of stereoscopic systems. We present a setup to simulate crosstalk including a specific software solution. It constitutes a platform to explore the effects of stereoscopic crosstalk in the augmented reality viewing conditions of a 3D HUD. As the setup allows the variation of numerous parameters, it provides a versatile research platform. By means of it, we investigate the variation of the visibility and acceptability thresholds of crosstalk over various parameters. Our results include the finding that they decrease with rising contrast affirming this behavior known for conventional stereoscopic displays for stereoscopic see‐through displays.     

True 3‐D scanned voxel displays using single or multiple light sources

Abstract— Conventional stereoscopic displays require viewers to unnaturally keep eye accommodation fixed at one focal distance while they dynamically change vergence to view objects at different distances. This forced decoupling of reflexively linked processes fatigues eyes, causes discomfort, compromises image quality, and may lead to pathologies in developing visual systems. Volumetric displays can overcome this conflict, but only for small objects placed within a limited range of viewing distances and accommodation levels, and cannot render occlusion cues correctly. Our multi‐planar True 3‐D displays generate accommodation cues that match vergence and stereoscopic retinal disparity demands and can display images and objects at viewing distances throughout the full range of human accommodation (from 6.25 cm to infinity), better mimicking natural vision and minimizing eye fatigue.     

Characterizing image quality of autostereoscopic displays by using the maximum luminance at each viewing position

A metric of the 3D image quality of autostereoscopic displays based on optical measurements is proposed. This metric uses each view's luminance contrast, which is defined as the ratio of maximum luminance at each viewing position to total luminance at that position. Conventional metrics of the autostereoscopic display based on crosstalk, which uses “wanted” and “unwanted” lights. However, in case of the multiple‐views‐type autostereoscopic displays, it is difficult to distinguish exactly which lights are wanted lights and which are unwanted lights. This paper assumes that the wanted light has a maximum luminance at the good stereoscopic viewing position, and the unwanted light also has a maximum luminance at the worst pseudo‐stereoscopic viewing position. By using the maximum luminance that is indexed by view number of the autostereoscopic display, the proposed method enables characterizing stereoscopic viewing conditions without using wanted/unwanted light. A 3D image quality metric called “stereo luminance contrast,” the average of both eyes' contrast, is proposed. The effectiveness of the proposed metric is confirmed by the results of optical measurement analyses of different types of autostereoscopic displays, such as the two‐view, scan‐backlight, multi‐view, and integral.     

Adaptive luminance difference between text and background for comfortable reading on a smartphone

This study proposes a model of adaptive luminance difference between text and background for comfortable reading on a smartphone display. The study is composed of two experiments. In Experiment I, the optimal luminance difference is identified in accordance with reading speed and preference. On the basis of the experimental results, the gradual decrease of luminance difference between text and background is developed. The change occurs while reading the text, and the model is applied to various illuminance levels. In Experiment II, the effect of adaptive luminance difference is validated in terms of reading speed, preference, and brainwave analysis using an electroencephalogram. Empirical evidence confirms that the developed model improves physiological comfort and psychological satisfaction, thereby it has a potential to be applied to the visual display industry.     

Effects of ambient illuminance on users' visual performance using various electronic displays

Abstract— This study investigated the effect of ambient illuminance (50, 500, 1500, 3000, 6000, and 9000 lx) on participants' visual performance using four electronic displays (conventional LCD under transmissive mode, conventional LCD under reflective mode, Ch‐LC display, and E‐ink display). Analysis results indicate that participants' visual performance shows significant difference under various ambient illuminance and electronic displays. The interaction between ambient illuminance and electronic display also has significant effect on participants' visual performance. When participants use the conventional LCD under transmissive mode, ambient luminance has no significant effect on participants' visual performance. However, participants' visual performance is significantly different under various ambient illuminances using the conventional LCD under reflective mode, Ch‐LC display, and E‐ink display. The conventional LCD under transmissive mode is the only choice at a lower illuminance of 50 lx. Higher illuminance (500 lx) for E‐ink displays may result in as good a performance as the conventional LCD under transmissive mode; nevertheless, much higher illuminance (1500 lx) for the conventional LCD under reflectance mode and Ch‐LC display may achieve better performance.     

A method for reproducing apparent continuous depth in a stereoscopic display using “Depth‐Fused 3D” technology

Abstract— A new method that can present fine depth increments in a stereoscopic display is proposed. In typical stereoscopic displays, depth can be presented by binocular disparity, but binocular disparity of less than one pixel cannot be displayed because, in general, electronic displays have discrete pixels. We combined binocular disparity and modulation of the edge luminance in DFD (depth‐fused 3D) displays. In an experiment, the perceived depth could be continuously changed by modulating the edge luminance only. Therefore, continuous depth can be produced by combining binocular disparity and modulation of edge luminance distribution.     

Relationship between parallax and spatial resolution on visual comfort of an autostereoscopic display

A primary reason for visual discomfort caused by viewing 3D contents in autostereoscopic displays is the conflict between accommodation and convergence. Parallax directly affects the degree of conflict. In this paper, three factors are investigated—parallax magnitude, changing parallax, and spatial resolution—which are supposed to exert substantial influence upon visual comfort. The aforementioned three factors are integrated into stereoscopic sequences generated by software. With the data on the subjective evaluation of comfort from the viewers, statistical method is used to obtain both the main effects and interactions among the three factors. According to the experimental results, changing parallax might play a more crucial role in visual comfort than parallax magnitude. Spatial resolution might alleviate the negative effects in which changing parallax brings about. The experiment indicates that parallax for autostereoscopic displays should be within 50′ in consideration of comfort.