Physiological effects of intermittently illuminated textual displays

Optical equipment was developed to simulate visual display terminals (VDTs) with reversed presentation (bright background and dark characters). The decay time and mean luminance were kept constant, while the oscillating frequency varied. During one experiment subjects had to read text aloud for 60min. Before and after the reading, near point distance, critical flicker fusion frequency (CFF), visual acuity, stereo depth perception, lateral heterophoria and contrast sensitivity were measured. The 30 subjects had then to report their subjective reactions on a questionnaire. The following frequencies were used: 0, 30, 60, 90, 180 Hz. In addition subjects read a normally printed text with a luminance of 75 or 150 cd/m². The main finding was that of a strong decrease of the CFF after exposure to 30 and 60 Hz. It is suggested that for reversed presentation the refresh rate should be higher than 90 Hz.     

Calculation of self‐luminous neutral scale: how many neutral steps can you see on that display?

One of the dimensions of visual perception usable for information display is neutral scale, the achromatic aspect of colour. An existing neutral scale calculation, CIE L*, relates reflected luminance to lightness magnitude and discrimination. But there is no similar international standard calculation for self‐luminous displays. In this article, we introduce a candidate self‐luminous neutral‐scale calculation, to complement CIE L*. We particularly examine its low‐contrast gain, the degree of crispening. This low‐contrast gain is a function of the background luminance, from which the target contrast is an increment or decrement. We demonstrate the use of the calculation to predict matches of neutral scale across different background luminances, and to model the successive thresholds of the Digital Imaging and Communications in Medicine Gray Scale Display Function. Finally, the proposed self‐luminous neutral scale is calculated to show the maximum number of discriminable differences, and the associated optimum background luminance, in representative ranges of display luminance.     

Effect of display polarity and luminance contrast on visual lobe shape characteristics

The effect of display polarity and luminance contrast on visual lobe (effective visual field) shape characteristics was studied using three levels of luminance contrast with combinations of positive and negative polarities. The binocular effective visual field for a detection task, with a peripherally presented target (V) embedded in a homogeneous competing background (Xs), was mapped on 24 imaginary axes passing through the fixation point. The results showed that visual lobes mapped using positive polarity were statistically larger in area, rounder and more regular in shape than those for negative polarity. The medium contrast condition lobes were more symmetric and regular than low contrast condition lobes, and lobe area and perimeter increased with increasing luminance contrast ratio. Under the interaction of positive polarity and high luminance contrast, visual lobes were found to be larger, smoother and rounder. The high level of luminance and contrast however resulted in a higher degree of visual discomfort. The results indicated that positive polarity and contrast of medium (26:1) to high (41:1) levels are possible display settings for better visual lobe characteristics and better anticipated search performance. Practitioner Summary: The effect of display polarity and luminance contrast on visual lobe shape characteristics was examined with uniform stimulus materials in this study. The results help to identify the optimum display settings for luminance contrast and display polarity to enhance lobe shape characteristics and hence search performance in industrial inspection tasks.     

The effects of color combinations,luminance contrast,and area ratio on icon visual search performance

The visual search of icons in a digital interface plays an important role in human-computer interaction. In this behavior study about the visual search of graphic symbols, the effects of the color combination, luminance contrast, and icon area ratio were investigated. A total of 28 participants (12 men and 16 women, ages ranging from 20 to 28 years, Mean = 22.4, SD = 1.7) were asked to perform an icon search task. Participants’ icon search accuracy and response times were measured as a function of the following independent variables: three levels of area ratios, four background colors, four foreground colors, and three levels of luminance contrast. The results showed that although there was no significant main effect of luminance contrast on the icon search accuracy, participants responded more quickly to medium luminance contrast than low or high luminance contrast. Similarly, the medium or low area ratio was more conducive to the participants identifying icons. Moreover, a strong interaction was observed between the effects of luminance contrast and icon area ratio. The icon search performance of the high luminance contrast improved significantly as the figure/background area ratio decreased. Icon color combinations also significantly affected visual search performance. White on black, yellow on black, turquoise on black, white on red, yellow on red, and white on purple resulted in better performance than other color combinations. The findings of this study provide useful guidelines for designing more efficient and user-friendly icons and interfaces in the future.     

Selecting colour codes for a computer-generated topographic map based on perception experiments and functional requirements

Abstract

This paper describes a series of human factors analyses that guided the selection of chromaticities and luminances for a computer-generated topographic map. By virtue of its impressive computational capabilities, this CRT-displayed digital map will greatly facilitate the navigational accuracy and situational awareness of army helicopter aviators during low level and nap-of-the-earth flight. Colour codes were assigned to the digital map's point, linear and area features according to guidelines derived from four colour naming and two symbol search experiments. The design of each study was structured around the map's functional requirements: the five linear feature colours should have high luminance and support absolute colour identification; the three point symbol colours should be identifiable at small sizes; and the four area colours should minimize colour distortions, with the two terrain colours luminance-shaded to depict elevation information. Within these constraints, the results of the colour naming studies yielded an initial set of map colour codes by identifying the most frequently occurring colour confusions arising from the perceptual distortions of brightness contrast, colour contrast and Gaussian spread. The symbol search studies further refined colour selection by identifying the specific foreground/background colour combinations that hinder search, and by quantifying the conditions under which a colour or monochrome map facilitates symbol search.     

Effects of refresh rates of a simulated CRT display with bright characters on a dark screen

Twenty-nine subjects carried out a 3 hour reading task at a simulated CRT. In the apparatus chopper discs generated oscillating luminances of bright characters of 30, 60, 90, 180 and 0 Hz. A further control experiment was conducted with a printed text. The oscillating luminances had an approximate decay time of 4 ms (to 10% of peak luminance). The character luminance was kept constant (75 cd/m²). In the simulated CRT all characters oscillated simultaneously.Before, during and after each reading task, the following parameters were determined: Near point distance, critical flicker frequency (CFF), visual acuity, heterophorias, contrast sensitivity, eye blinking rate, and subjective symptoms of discomfort. The reading speed was continuously recorded. Furthermore the CFF at the simulated CRT was determined.The range of individual CFF at the simulated CRT was found between 40 and 56 Hz. It is concluded that most models of VDTs have today refresh rates lying in a critical range of CFF. In every condition the reading task was found to have an effect on visual functions and caused visual discomfort. Differentiated results among the six conditions were only observed for CFF and visual discomfort. The visible flicker (30 Hz) produced the strongest effects while 180 Hz, 0 Hz and the printed text were associated with relatively small effects.     

对比度和白场设定对图像色彩度视觉感知影响的研究

由于显示器件(如电视机显示屏)的性能评判是与人的主观感觉不可分离的，所以它的研发方向也应以观察者的感受为指导，但由于不同文化背景的人的主观感觉有可能存在差异，因此研究这种差异对理解如何进一步改进显示器性能有着重要的指导意义。为了了解不同观测者的视觉感知差异，通过对彩色电视机上显示的静态图片进行的主观视觉评价实验，研究了不同对比度和白场设置对图像色彩度视觉感知的影响，并通过统计分析，发现了人们普遍喜好色彩饱和度大的图像这一结论，同时也得到了人们对不同白场设置和对比度等的喜好情况。实验中，首先将观察者分成专家(对显示器件原理以及色度学了解较多的人)和非专家两组进行评分，结果表明，专家评分的绝对值均值小于非专家的评分，这说明专家不能在大范围内区分不同的图像；最后把该结果与荷兰飞利浦研究所所做的相似实验作了比较，得到了东西方不同文化背景下视觉感知的差异的分析结果，但是对于CRT显示器件而言，高对比度将会产生较大的光点，而关于对比度与清晰度之间存在矛盾需要在以后的研究中进行证实。     

Assessment of drivers' visual perception of information displayed in LED traffic signs at road construction sites

This study investigated drivers' visual perception of information displayed in LED traffic signs under different levels of environmental luminance. Concerning the information displayed, the environmental luminance comprised four luminance contrasts, two arrow types, and three environmental luminances, which were used to identify the visibility of traffic signs at the reading distance. Regarding visible distance, visibility involved reading starting and end points, extent of glare, comfortable distance, and glare distance. According to the study results obtained by using a highly reliable glare assessment method and studying the LED traffic signs, the lower the luminance contrast of traffic signs was the higher glare the participants perceived. A luminance contrast of 6200:2066 cd/m² provided the farthest comfortable and glare distances, enabling drivers to notice the signs comparatively earlier and have sufficient time to react accordingly. Overall, arrow type “<<<” outperformed “←” because the former was easier for drivers to read and created less glare. Regarding environmental luminance, traffic signs displayed in high and medium luminance environments (i.e., extremely sunny and cloudy days, respectively) each featured their own advantage, whereas those displayed in low luminance environments (nights) have to be further improved.     

Limits of visual perception in the technology of visual display terminals

. The limits of visual perception in present VDT technology for man-machine communication are considered. Essentially, these limits concern the reading of the displayed information and follow from the prevailing display conditions as to (i) luminous contrast, (ii) character shape, (iii) text layout and (iv) text colour. The effect of these conditions on legibility is quantitatively described from research results, and practical suggestions are given for improving display legibility, through changes in contrast polarity, character shape, layout and the way colour is used. Finally, a plea is made for including experts in visual ergonomics in the teams developing new display devices in the future.     

The effect of text and background colour on visual search of Web pages

Usability and visual impact in Web pages are not necessarily compatible ideals. This paper investigates the effect of colour on the presentation of information in a navigation bar, and aims to contribute towards design guidelines for the use of colour on the Web. We studied the effect of the combination of text and background colour on visual search performance and subjective preference. Twenty-nine participants carried out a visual search task using mock Web pages. Analysis showed that higher contrasts between text and background colour led to faster searching and were rated more favourably. The results are discussed in terms of visual search processes and design recommendations are given.     

Visibility aspects of VDUs in terms of contrast and luminance

Characters on VDUs exhibit specific problems in terms of contrast and visibility evaluation. The photometric properties of CRT displays were analysed, resulting in the specification of local inner, local outer and mean character contrasts. On the basis of search experiments as well as of subjective appraisals it is shown that the inner detail contrast of characters is the determinant for the effect of contrast on visual performance and acceptance. The inner contrast also provides an adequate criterion to optimize the adjustment of contrast, including the effects of lighting in the room. In order to evaluate the visibility level of VDU characters an analytical model is presented based on the threshold numbers between critical character details. Recommendations are given for optimized adjustments of character contrast and background luminance.     

基于视觉感知的梯度结构相似度图像质量评价*

尽管SSIM(Structural Similarity)图像质量评价算法结构简单,评价性能优于一般客观评价算法,但该算法没有考虑人类视觉系统HVS(human visual system)对视觉感知的影响,且其算法定义中对“结构信息”的表述过于简单,并不能完全描述自然图像的结构信息。在SSIM算法的基础上,结合亮度和对比度掩蔽等视觉感知信息构造视觉感知（Visual Perception）函数,提出基于视觉感知的梯度结构相似度评价方法VI_GSSIM（Visual Perception and Gradient based SSIM, VI_GSSIM）。该方法通过图像质量与图像内容和失真类型的相关性,结合图像的误差可视性与内容可视性构造视觉感知函数,对HVS底层视觉系统建模,同时利用梯度重新定义结构信息,得到基于视觉感知的梯度结构相似度模型,对图像进行质量评价。实验结果表明提出的VI_GSSIM算法比SSIM更符合人眼的视觉特性,尤其适合评价降质较严重的图像。     

Filters on computer displays - effects on legibility, performance and comfort

The hypothesis is that using a contrast-enhancing filter (CEF) on a computer display will improve display legibility, reading speed and visual comfort. Twenty subjects performed reading tasks, letter counting tasks, and legibility measurements on eight display conditions: a cathode ray tube (CRT) and liquid crystal display (LCD) matched for size and luminance - each at high luminance, with two different CEFs and a lower luminance to match one of the CEFs. The CEFs decreased both luminance and contrast when applied to the displays with the brightness set high, although the contrast was better with the filters compared to a matched luminance display without a filter. The legibility measurements support the positive effect of the CEFs due to improved contrast but the larger negative effect due to reduction in luminance results in a net loss of legibility. Performance on the reading and letter counting tasks was not improved with the CEFs.     

Visual search strategies and eye movements when searching Chinese character screens

Most visual search studies have been restricted to alphanumeric stimulus materials. Research related to scanning patterns of Chinese characters is sparse. This study is an attempt to understand the differences and similarities in visual search of Chinese characters having a varying degree of complexity among Hong Kong Chinese, Mainland Chinese and Chinese reading non-Chinese people. Eighteen participants were tested on Chinese character screens with three layouts (row, column, and uniform separation) and two word complexities (high and low). The 18 participants comprised six Hong Kong Chinese, six Mainland Chinese and six non-native Chinese readers. Performance data and eye movement data were recorded. The percent correct and search time were the two performance measures. A new measure, called HV-ratio was developed to characterize eye movements. The results show that Hong Kong Chinese use predominantly horizontal search patterns while the Mainland Chinese change their search pattern depending on the layout presented. Non-native Chinese readers, on the other hand, do not seem to show any preference on scanning strategy for a given layout. Word complexity did not show any significant effect on search time. Potential reasons for these differences and design implications are discussed.     

Optimization of operating parameters of video display units in text reading task: Luminance contrast,viewing distance,and character size

Abstract— The purpose of this study is to determine the reading performance of operators on a desktop computer. The effects of luminance contrast, viewing distance, and character size on the speed of reading were investigated. The luminance contrast between the background and character was varied while color contrast was held near‐constant. Stimuli with different levels of character size, viewing distance, and luminance contrast were considered while assessing the readability performance. The luminance contrast between the background and character (0.01, 0.15, and 1.00), character sizes (0.2, 1.5, and 4°), and viewing distance (40, 50, and 60 cm) were used, and the performance of the operators were recorded in terms of words per minutes (WPM). Standard workplace design recommendations to position the center of the visual display terminal (VDT) 15° and 40° below horizontal eye level were used for the visually intensive readability task. An orthogonal array, the signal‐to‐noise (S/N) ratio, and the analysis of variance (ANOVA) were employed to investigate the above‐mentioned operating parameters to determine the optimum readability performance. The results indicated that performance was better at a 15° viewing angle as compared to a 40° viewing angle.     

基于视觉相似性的半色调图像评价方法

为衡量半色调图像质量或加网算法的优劣,提出平均亮度相似性误差、平均对比度相似性误差和视觉相似性误差以衡量半色调图像与连续调图像之间的视觉相似性。该方法根据人眼视觉局部适应性特征,把图像划分子区域,利用亮度掩蔽和对比度掩蔽的特征,获得各子区域的亮度相似性误差和对比度相似性误差,最终获得平均亮度相似性误差、平均对比度相似性误差和视觉相似性误差分别评价半色调图像与原连续调图像在亮度和纹理的视觉相似性,及半色调图像中的局部缺陷。分别通过与峰值信噪比(PSNR)和权重信噪比(WSNR)在亮度相似性上进行比较,与全局质量因子(UQI)和图像结构相似(SSIM)在评价纹理相似性上进行比较,发现所提质量评价方法比较接近人眼视觉评价的结果。     

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).     

The effects of age, viewing distance, display type, font type, colour contrast and number of syllables on the legibility of Korean characters

This study evaluated the effects of age (20s and 60s), viewing distance (50 cm, 200 cm), display type (paper, monitor), font type (Gothic, Ming), colour contrast (black letters on white background, white letters on black background) and number of syllables (one, two) on the legibility of Korean characters by using the four legibility measures (minimum letter size for 100% correctness, maximum letter size for 0% correctness, minimum letter size for the least discomfort and maximum letter size for the most discomfort). Ten subjects in each age group read the four letters presented on a slide (letter size varied from 80 pt to 2 pt). Subjects also subjectively rated the reading discomfort of the letters on a 4-point scale (1 = no discomfort, 4 = most discomfort). According to the ANOVA procedure, age, viewing distance and font type significantly affected the four dependent variables (p < 0.05), while the main effect of colour contrast was not statistically significant for any measures. Two-syllable letters had smaller letters than one-syllable letters in the two correctness measures. The younger group could see letter sizes two times smaller than the old group could and the viewing distance of 50 cm showed letters about three times smaller than those at a 200 cm viewing distance. The Gothic fonts were smaller than the Ming fonts. Monitors were smaller than paper for correctness and maximum letter size for the most discomfort. From a comparison of the results for correctness and discomfort, people generally preferred larger letter sizes to those that they could read. The findings of this study may provide basic information for setting a global standard of letter size or font type to improve the legibility of characters written in Korean. STATEMENT OF RELEVANCE: Results obtained in this study will provide basic information and guidelines for setting standards of letter size and font type to improve the legibility of characters written in Korean. Also, the results might offer useful information for people who are working on design of visual displays.     

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.     

Whole-body vibration and visual performance: an examination of spatial filtering and time-dependency

Two experiments have examined the effects of whole-body vibration on visual performance. The first experiment concerned alphanumeric reading performance and contrast thresholds for gratings subtending 7-5, 10 and 12-5 cycles per degree (c deg)^?1. Seated subjects were exposed to vertical sinusoidal whole-body vibration (4 Hz, 2-5 ms^?2 r.m.s.). Greatest reading errors occurred with characters exhibiting a high spatial complexity in their vertical axis. Reductions in contrast sensitivity due to vibration increased with increasing spatial frequency, the greatest loss occurring with horizontally orientated gratings.

In the second experiment, contrast thresholds for horizontally orientated gratings subtending 1-5 and 12-5cdeg^?1 were obtained from ten subjects at five-minute intervals during a 60-minute whole-body vibration exposure (20 Hz I -7 m s ^?2 r.m.s.), a 20-minute pre-exposure and a 60-minute post-exposure period. There were no significant changes in contrast thresholds for gratings subtending 1-5cdeg^minus;1 during or after vibration exposure. A large variation was found in the effect of vibration upon performance with the higher spatial frequency grating both during and after vibration exposure. Significant correlations between vertical head motion and contrast sensitivity were obtained with five of the ten subjects, suggesting that time-dependent changes in seat-to-head transmissibility were partly responsible for the results. Other time-dependent changes were found with the high spatial frequency grating. Possible explanations are discussed.