Comparison of reflective PNLCDs and reflective single‐polarizer Heilmeier guest‐host displays

In this paper, the applicability of a zero‐polarizer reflective display (PNLC) and a single‐polarizer reflective display (Heilmeier guest host) for direct‐view applications is analyzed. A measurement set‐up is designed to analyze the applicability of all types of reflective displays. Simulation of the different types of illumination caused by the environmental light is essential for this set‐up. The measurements indicate that the contrast ratio and reflectance greatly depend on the type of illumination. It is demonstrated that the worst‐case illumination for one display technology may be the best‐case illumination for another one and vice versa.     

Effect of gloss and diffuse reflectance of display frames on visual comfort

Abstract— A series of 12 display frames of different combinations of gloss levels and diffuse reflectance levels was mounted on a display to test the visual comfort of 31 test subjects. The frames were tested in a controlled environment where a light reflex was purposefully visible on the frame. The intensity of the light reflex was controllable by the user, and the dial setting was recorded for each frame. The frames were also shown in two different test office environments, one light and one dark. Qualitative comments about the frames were recorded. A gloss level of 30 gloss units corresponded to about 30% of test subjects that wanted no reflex at all to be visible on the frame. There was a significant effect of frame gloss on the acceptable light level of the reflex. When the acceptable‐light‐level dial setting was converted to luminance contrast, the acceptable luminance contrast on the frames decreased with increasing gloss, and this effect was more pronounced for black frames.     

Investigation of perceived image quality and colourfulness in mobile displays for different cultures,ambient illumination,and resolution

This study explored the effects of culture, ambient illumination, and resolution on perceived image quality and colourfulness of mobile displays. Thirty Taiwanese and 30 American students participated in the experiment. Two types of culture (Taiwanese and American), two types of illumination level (1500 lux and 7000 lux), and five types of resolution level (320×240, 260×208, 200×160, 140×112, and 80×64) were investigated in the experiment. Interactions between culture and resolution, and between illumination and resolution, were found for both perceived image quality and colourfulness. The results indicated that subjects were able to detect smaller differences in perceived image quality but not for colourfulness, and Taiwanese subjects could detect smaller differences than could the American subjects for both perceived image quality and colourfulness. The results further indicated that Taiwanese subjects were able to detect smaller differences at most of the resolution levels for colourfulness in 1500 lux than were the American subjects.

Practitioner Summary: This study found, from culture differences and ergonomics considerations, that Taiwanese subjects could detect smaller differences than could American subjects when evaluating perceived image quality and colourfulness on mobile displays. Mobile display manufacturers can use the results of this study as a reference for future mobile display design.     

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.     

非线性复合邻域人脸光照补偿

变化的光照是提高人脸正确检测率的瓶颈,提出了非线性复合邻域光照补偿方法来解决人脸检测的光照问题。非线性复合邻域光照补偿方法用对数函数做为基函数,设置的平移系数和分界值系数可以同时对过亮和偏光的图像进行补偿,引入了邻域光照补偿公式解决了传统非线性方法不能针对同一灰度值像素在不同局部应该进行不同补偿的问题。实验结果表明,该方法对过暗和过亮的人脸图像都可以进行有效的光照补偿,熵比较优于传统非线性光照补偿、Gamma校正和直方图归一化。     

Effects of electronic‐book display and inclination on users' comprehension under various ambient illuminance conditions

Abstract— This study used several electronic‐book (e‐book) displays (a conventional LCD under transmissive mode, a conventional LCD under reflective mode, a Ch‐LC display, and an e‐ink display) to investigate the effect of e‐book inclination (105° and 135°) and ambient illuminance (200, 800, 1500, and 2200 lux) on the comprehension of subjects. Results indicate that the ambient illuminance does not significantly affect the comprehension of subjects. However, their comprehension differed significantly when using different e‐book displays. In addition, the interaction between illuminance and e‐book display had a significant effect on their comprehension. When the ambient illuminance was set at 800, 1500, and 2200 lux, the subjects' comprehension for reading different e‐book displays did not show a significant difference. When the ambient illuminance was set at 200 lux, however, their comprehension for reading a Ch‐LC display, an e‐ink display, and a conventional LCD under transmissive mode were better than their comprehension of reading a conventional LCD under reflective mode. Regarding the inclination for using e‐books, the subjects' comprehension was better under 105° than that under 135°.     

Adapting softcopy color reproduction to ambient illumination

Abstract— The perceived colors of an image seen on a self‐luminous display are affected by ambient illumination. The ambient light reflected from the display faceplate is mixed with the image‐forming light emitted by the display. In addition to this direct physical effect of viewing flare, ambient illumination causes perceptual changes by affecting the adaptation state of the viewer's visual system. This paper first discusses these effects and how they can be compensated, outlining a display system able to adjust its output based on prevailing lighting conditions. The emphasis is on compensating for the perceptual effects of viewing conditions by means of color‐appearance modeling. The effects of varying the degree of chromatic adaptation parameter D and the surround compensation parameters c and N_c of the CIECAM97s color‐appearance model were studied in psychophysical experiments. In these memory‐based paired comparison experiments, the observers judged the appearance of images shown on an LCD under three different ambient‐illumination conditions. The dependence of the optimal parameter values on the level of ambient illumination was evident. The results of the final experiment, using a category scaling technique, showed the benefit of using the color‐appearance model with the optimized parameters in compensating for the perceptual changes caused by varying ambient illumination.     

Effects of Font Size,Stroke Width,and Character Complexity on the Legibility of Chinese Characters

This study investigated the effects of font size, stroke width, and character complexity on the legibility of Chinese characters. A within‐subjects design experiment was employed. Thirty‐six subjects participated in the experiment and completed the character‐search tasks in the pseudo‐texts. The search time per target character, correct response number, and correct response rate were used to measure the legibility. The results indicated that the font size and character complexity had significant effects on the legibility, while the effect of stroke width was not significant. All the two‐way interactions among the three display factors had significant effects on the legibility. Stroke width is critical to the legibility for characters with high‐level complexity, whereas font size is the critical factor influencing the legibility for characters with low‐level complexity. The combination of 12pt font size and 1:10 stroke width resulted in the best legibility for both character complexity levels. The findings provide useful information for the font design of Chinese texts displayed on a visual display terminal to improve the legibility.     

Visual gamma measurement and methods to compare gamma models

Abstract— The correct estimation of the gamma exponent describing the tone‐reproduction curve of a display is an important step in color management. Several methods for visual gamma estimation have been proposed. In this study, the theoretical merits and practical problems of a number of these methods are discussed and compared, and improvements are suggested. A new method to compare gamma models with different numbers of parameters is introduced. In an experiment, spatial and temporal brightness‐matching methods were tested with 32 untrained subjects working on a CRT and an LCD with different resolutions under office and low‐illumination conditions. Illumination had no effect on gamma estimations. Subjects had great difficulties with spatial brightness matching at low resolutions. Temporal and spatial visual brightness matching for untrained subjects showed a larger gamma than photometric fits.     

Electro‐optical transfer function preferences for LCD TVs: The effect of display brightness and surround illumination on preferred gamma

Abstract— Recent commercial liquid‐crystal‐display (LCD) televisions are larger and brighter than traditional televisions, thus impacting the viewing conditions in which they are viewed. These changes in viewing conditions may require different electro‐optical transfer functions (EOTFs) for LCD TVs than those for conventional TVs. Here, the way various EOTFs affect the preferred image quality of test images with changes in brightness and surround illumination conditions are examined. The first method used a gain, offset, and gamma (GOG) function with a range of gamma values, and the second method altered the intrinsic EOTFs. Image preference for the simulated EOTFs was determined using a paired‐comparison experiment for ten images. The first experiment took place in a darkened room at two display luminance levels. The results indicated that a gamma of 1.6 was most preferred overall although more so at a lower screen luminance level. In a second experiment, the procedure was repeated with a dim surround of 10% of the display's white point. With this surround, preference for a gamma value of around 1.6 at both screen luminance levels was more enhanced. These results indicated that image preference for different EOTFs is dependent on display luminance and that this dependence is maintained with a dim surround.     

High-Resolution Volumetric Computation of Offset Surfaces with Feature Preservation

We present a new algorithm for the efficient and reliable generation of offset surfaces for polygonal meshes. The algorithm is robust with respect to degenerate configurations and computes (self‐)intersection free offsets that do not miss small and thin components. The results are correct within a prescribed ε‐tolerance. This is achieved by using a volumetric approach where the offset surface is defined as the union of a set of spheres, cylinders, and prisms instead of surface‐based approaches that generally construct an offset surface by shifting the input mesh in normal direction. Since we are using the unsigned distance field, we can handle any type of topological inconsistencies including non‐manifold configurations and degenerate triangles. A simple but effective mesh operation allows us to detect and include sharp features (shocks) into the output mesh and to preserve them during post‐processing (decimation and smoothing). We discretize the distance function by an efficient multi‐level scheme on an adaptive octree data structure. The problem of limited voxel resolutions inherent to every volumetric approach is avoided by breaking the bounding volume into smaller tiles and processing them independently. This allows for almost arbitrarily high voxel resolutions on a commodity PC while keeping the output mesh complexity low. The quality and performance of our algorithm is demonstrated for a number of challenging examples.     

陆地卫星多光谱扫描图象错位条带的纠正

本文介绍用电子计算机对陆地卫星多光谱扫描遥感图象的错位条带进行纠正的方法.错 位条带出现的位置和错动距离是随机的.纠正这种条带需要知道两个值:错位所在的行号和 错开的象元数.在显示屏幕上用人眼做这项工作费时费力.本文介绍用相关技术或序贯相 似性检测算法自动计算上述两个数值,进而完成错位条带纠正的方法.     

Image‐color‐quality modeling under various surround conditions for a 2‐in. mobile transmissive LCD

Abstract— This study aims to develop an image‐color‐quality (ICQ) model for a 2‐in. mobile transmissive liquid‐crystal display (LCD). A hypothetical framework for ICQ judgment was made to visually assess ICQ based the cognitive processes of the human visual system (HVS), and then an illumination adaptive ICQ model applicable for various surround conditions was developed. The memory color reproduction ratio (MCRR) of a locally adapted region of interest in a complex image reproduced on a mobile display was first computed. The colorfulness index and luminance contrast for all of the pixels in the image were then calculated by a global adaptation process. Finally, an ICQ model including all of the three attributes was developed under dark conditions using an assessed set of psychophysical data. The model gave more accurate performance than the mean accuracy for all of the observers. It was also visually tested under three different outdoor conditions, including overcast, bright, and very bright conditions, and the illuminance level range was from 7000 to 35,000 to 70,000 lx. The effect of outdoor illumination could be quantified as an exponential decay function and the ICQ model could be extended to cover a wide variety of outdoor illuminations conditions.     

Overcoming latency with motion prediction in directional autostereoscopic displays

Imaging delivering to correct retina assisted with tracking technique is a common practice for autostereoscopic displays with stereo two‐view data format. Due to various latencies produced in camera buffering, computer processing, data transmission, and illumination refreshing, delayed image delivery will give rise to a substantial degradation of the 3D display experience. This is particularly obvious for directional backlight 3D displays where significant flickering is resulted as a result of the inherent latency. This work systematically analyzes the source of latency by quantitatively measuring the exact latency value in a typical directional backlight autostereoscopic display. Based on accurate measurement, a motion prediction solution is proposed to improve the synchronization between the backlight illumination and viewer's eye location. Motion prediction helps overcome the lag between the center of illumination and viewer's eye, providing a flicker‐free viewing experience for both a stationary and a moving viewer.     

Survey of actual viewing conditions at home and appropriate luminance of LCD‐TV screens

Abstract— To understand actual viewing conditions at home is important for TV design. And the preferred luminance level of LCD TVs under actual viewing conditions is also important in order to obtain both good picture quality and low power consumption. The actual viewing conditions of households and the preferred luminance levels was investigated. In a field test of 83 households, the display luminance, screen illuminance, and viewing locations were measured on site. In laboratory experiments, young and elderly subjects adjusted the luminance of an LCD‐TV screen to their preferred levels under different screen illuminance levels, angular screen sizes, and average luminance levels (ALL) of the images. As a result, two equations, which represent the preferred luminance level of LCD‐TV screens corresponding to different viewing conditions for young and elderly subjects were obtained. When the ALL of the images was 25% and the screen illuminance and angular screen size were set at 100 lx and 20°, respectively, the preferred luminance was 1 60 cd/m² for the young subjects and 248 cd/m² for the elderly subjects. By using the setting of the preferred luminance of an LCD TV under actual viewing conditions, it is possible to conserve energy consumption.     

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.     

Antireflection displays with ambient contrast enhancement for extended device battery lifetime and reduced energy consumption

Antireflection (AR) coatings can improve the viewing experience of a display, including mobile electronic devices such as smartphones, tablets, and laptops that are typically operated on battery power and protected with chemically strengthened glass. In this work, we discuss the trade‐offs between optimal user viewing experience in brightly lit environments and battery lifetime for an AR versus a non‐AR mobile display. We show that under 400–1,000 lux ambient illumination, an AR‐based display can be operated at >30% lower luminance than a non‐AR display with similar human perception of contrast based on a perceptual contrast length model, resulting in a potential improvement of >15% in device battery lifetime and a similar proportion of energy savings.     

Methods for measuring performance of LCoS microdisplays

Abstract— Liquid‐crystal‐on‐silicon (LCoS) microdisplays have unique measurement requirements not shared by direct‐view flat‐panel displays. We developed a series of measurement techniques for measuring reflectance, contrast ratio, and uniformity of LCoS microdisplays. Reflectance is determined by comparing light reflected off of the microdisplay in its “white” state with that reflected off of a calibrated mirror. Several corrections are applied to take into account polarization differences between the reference measurement and display measurement. Contrast ratio is determined by measuring display reflectance in the “white” and “black” states. Reflectance and contrast data can be reduced to scalar values once the spectral content of the intended illumination source is defined. There are several methods for measuring uniformity of contrast and reflectance. An approach that we have developed closely follows the sampled uniformity measurements outlined by VESA for direct‐view displays (Ref. 1).     

Prediction Error Based Performance Monitoring,Degradation Diagnosis and Remedies in Offset‐Free MPC: Theory and Applications

We present in this paper a control performance monitoring method for linear offset‐free model predictive control (MPC) algorithms, in which the prediction error sequence is used to detect whether the internal model and the observer are correct or not. When the prediction error is a white noise signal, revealed by the Ljung‐Box test, optimal performance is detected. Otherwise, we use a closed‐loop subspace identification approach to reveal the order of a minimal realization of the system from the deterministic input to the prediction error. When such order is zero, we prove that the model is correct and the source of suboptimal performance is an incorrect observer. In such cases, we suggest an optimization method to recalculate the correct augmented state estimator. If, instead, such order is greater than zero we prove that the model is incorrect, and re‐identification is suggested. A variant for (large‐scale) block‐structured systems is presented, in which diagnosis and corrections are performed separately in each block. Two examples of different complexity are presented to highlight effectiveness and scalability of the method.