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A preview of some of the most interesting papers appearing in the
November 2008 issue of the 
Journal of the SID. 
To obtain access to these articles on-line, please go to www.sid.org

Edited by Aris Silzars


Influence of the monocular near-to-eye display position on the visual system during dual-task performance

M. Pölönen
V. Aaltonen
G. Nyman
J. Häkkinen (SID Member)

Nokia Research Center

Abstract — In this research project, the influence of different monocular near-to-eye display (NED) positions on user comfort has been investigated. In total, 43 subjects participated in tests; 22 used above and 21 below NED positions during dual-task performance for 40 minutes. SSQ and VSQ questionnaires were used to compare the eyestrain and other sickness symptoms before and after the task performance for both display positions. According to the subjective test results, the NED position above the eye causes more symptoms than the position below the eye.

People repeatedly face situations where they need or could benefit from more information. One possibility to gain additional information is to exploit an NED. NEDs could be used in very different environments with different applications without outside interruptions. A type of NED, monocular, bi-ocular, or binocular, on one hand sets limits, but on the other hand gives the user freedom to choose the most suitable presentation mode for a specific media. Like standard monitors, NEDs could also cause unwanted consequences if they are not used appropriately.

 

p1084_fig_2_pdf

FIGURE 2 — The participants viewed a small NED placed either approximately 5° above or approximately 15° below the horizon line of sight. The ViewSonic display's middle point was approximately 5° below the horizon line.

 


Application of radial basis functions to shape description in a dual-element off-axis eyewear display: Field-of-view limit

Ozan Cakmakci
Sophie Vo
Kevin P. Thompson
Jannick P. Rolland (SID Member)

University of Central Florida

Abstract — Previously, it was demonstrated that radial basis functions may be preferred as a free-form shape descriptor for a single-mirror magnifier, justified by a performance increase measured by the MTF, when compared to other conventional descriptions such as multivariate polynomials (e.g., Zernike polynomials or x– y polynomials). The benefit in performance increase can be used to expand the pupil diameter from 8 to 12 mm given a 20° field of view and a 15-mm eye clearance or to increase the field of view. The main contribution in this paper is the investigation of the field-of-view limit in a dual-element magnifier where the free-form mirror is described with radial basis functions. Our main result in this paper is an estimate of the field-of-view limit of the dual-element magnifier to be approximately 25° full-field diagonal, given the specific geometry described in the paper. The impact of the astigmatic node placement in a rectangular image field on the modulation transfer function is also analyzed for the particular dual-element magnifier geometry.

Regardless of complexity (i.e., types or number of surfaces), an optical system can always be characterized by an effective focal length along with principal planes and nodal points. A magnifier forms a virtual image when the object lies inside of its focal length as shown in Fig. 1. Our approach is to consider one or two element magnifier designs and investigate their performance, field of view, and pupil-size limits.

 

p1089_fig_1

FIGURE 1 — Illustration of the principle of operation of a magnifier.

 


Reading experience with curved hand-held displays

Jukka Häkkinen (SID Member)
Monika Pölönen
Marja Salmimaa (SID Member)
Jukka Hautanen (SID Member)

University of Helsinki

Abstract — The aim of this study was to measure reading experiences on curved paper-like displays. The experimental materials were mockups that consisted of printed paper attached to a curved plastic surface. The experiment participants held the mockups in their hands and evaluated the reading experience with them. Twelve font sizes, two curvature magnitudes, and two curvature directions were used in the experiment. The results showed that reading text on a curved surface was easier when the curvature direction is perpendicular to the text direction. It was also found that concave surfaces were regarded as better in cases where the text direction was the same as the curvature direction.

The anchoring stimuli were flat and had stimulus text in 12 different font sizes starting from 6 and ending at 22 [Fig. 1(a)]. The text was printed on a gray background. After the initial anchoring stimuli, we presented the curved stimuli [Figs. 1(b)–1(e)], which consisted of five different font sizes that were chosen based on pilot experiments, which indicated that the greatest change in the subjective opinion changes between font sizes 6 and 12 after which the subjective reading experience did not increase and even decreased with larger fonts.

 

p1100_fig_1

FIGURE 1 —Stimuli used in the experiment. (a) Anchoring stimulus with flat plastic background, (b) convex stimulus with equal text and curvature direction, (c) concave stimulus with equal text and curvature direction, (d) convex stimulus with opposite text and curvature direction, (e) concave stimulus with opposite text and curvature direction, (f) comparison stimulus with flat plastic background.

 


The effect of stereoscopic viewing in a word-search task with a layered background

Sachi Mizobuchi
Shinya Terasaki
Jukka Häkkinen (SID Member)
Erkki Heinonen
Johan Bergquist (SID Member)
Mark Chignell

Keio University

Abstract — The benefits of stereoscopic viewing were explored in searching in words superimposed over a background. In the first experiment, eight participants searched for text in a normal 2-D display, a 3-D display using a parallax barrier, and a darkened 2-D display of equivalent brightness to the 3-D display. Word-search performance was significantly faster for the bright 2-D display vs.the 3-D display, but when brightness was controlled, performance on the 3-D display was better relative to the 2-D (dim) display. In a second experiment, the effect of floating text vs. sinking background disparity was assessed across four background conditions. Twenty participants saw only the floating-text (FT) condition and 20 participants saw only the sinking-background (SB) condition. Performance of the SB group was significantly better than that of FT group, and the advantage of SB disparity was greater with the more-complex backgrounds. Thus, when a parallax-barrier 3-D display is used to view text or other figural information overlaid on a background, it is proposed that the layer of primary interest (foreground) should be displayed with zero disparity (on the physical display surface) with the secondary layer (background) appearing to be sunk beneath that surface.

Multiple layers of information within a fixed area theoretically multiply that area by the number of layers. However, problems such as visual parallax and limited visual attention for simultaneous multi-level viewing mean that the measurable benefit of layered 3-D interaction is likely to be much less than might be predicted by simply summing the areas of the multiple layers in the display.

 

p1105_fig_1

FIGURE 1 — The concept: Layering application information on a handheld device.

 


Motion-blur characterization with simulation method for mobile LCDs

Yuning Zhang (SID Student Member)
Xiaohua Li (SID Member)
Yiqin Xu
Yabin Shi
Wen Song
Wei Lei

Southeast University

Abstract — A simulation method based on measured liquid-crystal responses and human-vision properties was proposed to characterize the motion blur of LCDs. A perceptual experiment was implemented to validate the simulation model within different viewing conditions by changing the visual angle. The results indicate that the smaller visual angle of the mobile display has no statistic significant effect on smooth-pursuit eye tracking when perceiving a moving block on a screen. The calculation process of quantitative metric was presented based on the measured light behavior and the simulation model. In the end, the different motion-blur reduction approaches were evaluated for mobile LCDs.

Motion blur is caused by the combination of light behavior of the LCD and the human-vision property. Consider a one-dimensional image displayed on a screen. For a sample-and-hold type display, the light emission will hold on for one frame period. When the image moves on the screen from left to right at the speed of 2 ppf (pixel per frame), the image content will hop from left to right immediately at the beginning of each frame and then hold for one frame period. So the signal in a LCD is discrete in both spatial domain (quantified in pixels) and temporal domain (quantified in frames).

 

p1116_fig_2

FIGURE 2 — Motion-blur generation when liquid-crystal response delay is taken into account. The lower part indicates the liquid-crystal response and the integration region with the eye is smoothly tracking.

 


OLED lifetime issues from a mobile-phone-industry point of view

Antti Laaperi

Nokia Device R&D

Abstract — Lifetime issues have been a hot topic throughout the history of OLEDs. The rapid development of lifetimes since 2002 has enabled OLED displays to become acceptable for mobile phones. The lifetime requirements of 30,000 hours expressed by the representatives of mobile-phone-terminal makers were felt to be unrealistic to be obtained in 2003, since the lifetime of the blue color was below 1000 hours. Today, 5 years later, lifetimes of AMOLED panels are over 50,000 hours. OLED displays are suffering from a burn-in effect due to limited lifetime. After 2003, it was understood by the panel and terminal makers that instead of lifetime, burn-in sensitivity became the limiting factor from an AMOLED-panel usability point of view. The burn-in effect becomes visible at 2–3% luminance degradation levels between adjacent pixels. To take this effect into account in mobile-phone applications, the lifetime needs to be increased from 30,000 to 60,000 hours, and suitable algorithms need to be used for the display of the terminal. There is also pressure to double the peak luminance values used in the terminals in order to improve the performance of the screen in outdoor environments. The roles of the material developers, panel makers, and terminal makers are reviewed in this paper from a lifetime perspective.

 

TABLE 1 — Development of the lifetime (hours) for small-molecule OEL materials during 2004–2007.

p1126_table_1


TABLE 2 — Development of lifetime (hours) of polymer-OEL material during 2002–2007. The luminance reference for all the values in Table 2 is 1000 cd/m2.

p1126_table_2


 


Power-saving primary design for displays enclosing a target color gamut

Senfar Wen (SID Member)

Chung Hua University

Abstract — Display primaries are optimized for the trade-off between the total primary power and color gamut under the requirement that a target color gamut is enclosed by the color gamut of the display. LED displays and HDTV color gamut are taken as examples. Compared to the display using a set of typical commercial RGB LEDs, it was found that a total optical (electrical) power of 23.6% (15.6%) can be saved for the display using optimal RGB LEDs. Although the size of the display color gamut is sacrificed, the color gamut of the display using optimal RGB LEDs still encloses the HDTV color gamut. The combined effect of the LED luminous efficiency and white-point condition on the determination of the optimal LED wavelengths and bandwidths is also studied.

For the display where its chromaticity triangle encloses the HDTV chromaticity triangle, its color gamut may not completely enclose the HDTV color gamut in a perceptual color space. Thus, we represent the color gamut of a display in the CIELAB color space in this paper. Figure 2 shows the HDTV color gamut. The color-gamut size is represented by a discernible color number instead of the chromaticity triangle area. The discernible color number represents the number of discernible colors as defined based upon calculations using the CIE94 color-difference formula in the CIELAB color space.

 

p1132_fig_2

FIGURE 2 — Color-gamut cross sections of constant lightness (L*) in CIELAB color space for the HDTV color standard. The corresponding values of L* are shown near the boundaries of the cross sections. Dashed lines show the loci of primary ramps.

 


Color performance of an MVA-LCD using an LED backlight

Ruibo Lu (SID Member)
Xiangyi Nie
Shin-Tson Wu (SID Fellow)

University of Central Florida

Abstract — The color performance, including color gamut, color shift, and gamma curve, of a multi-domain vertical-alignment (MVA) liquid-crystal display (LCD) using an LED backlight are calculated quantitatively. Simulation results indicate that an LED backlight exhibits better angular color uniformity and smaller color shifts than a CCFL backlight. Color gamut can be further widened and color shift reduced when using a color-sequential RGB-LED backlight without color filters, while the angular-dependent gamma curves are less influenced using different backlights. The obtained quantitative results are useful for optimizing the color performance and color management of high-end LCD monitors and LCD TVs.

In evaluating the color uniformity of an LCD monitor or TV, the observers care more about the color performance in the horizontal and vertical directions. Therefore, the color shift in the horizontal direction is usually measured. Figure 5 shows the simulated angular dependent Δuv′ of an MVA-LCD backlit by different light sources as observed from the horizontal (φ = 0°) viewing direction at G63 and G255, respectively. The RGB curves are more or less symmetric along θ = 0° and the Δuv′ value increases as θ increases. It is interesting to note that no matter which backlight is used, blue color always has the largest Δuv′ value, followed by green and then red.

 

p1143_fig_5

FIGURE 5 — Color shift for RGB primaries at the different gray levels under different backlights along the horizontal direction. Gray level, G255.

 


Compact modeling of amorphous-silicon thin-film transistors with BSIM3

Rahul Shringarpure
Sameer Venugopal (SID Member)
Korhan Kaftanoglu
Lawrence T. Clark
David R. Allee (SID Member)
Edward Bawolek

Flexible Display Center, Arizona State University

Abstract — A novel approach of modeling a-Si:H TFTs with the industry-standard BSIM3 compact model is presented. The described approach defines the a-Si:H TFT drain current and terminal charges as explicit functions of terminal voltages using a minimum set of BSIM3 parameters. The set of BSIM3 parameters is chosen based on the electrical and physical characteristics of the a-Si:H TFT and their values extracted from measured data. By using the selected BSIM3 model parameters, the a-Si:H TFT is simulated inside SPICE to fit the simulated I–V and C–V curves with the measured results. Finally, the extracted BSIM3 model is validated by simulating the kickback voltage effect in an AMLCD pixel array.

The modeled a-Si:H TFT is fabricated with a low-temperature, 180°C process compatible with a flexible transparent substrate.The gate metal is molybdenum patterned on the substrate and is placed underneath the a-Si:H. The gate dielectric is silicon nitride and the active layer is hydrogenated amorphous silicon deposited with plasma-enhanced chemical vapor deposition. The source/drain metal is sputtered on as an N+ a-Si/Al bilayer. Depending on the application, another metallization step using indium tin oxide and molybdenum (ITO) is carried out [see Fig. 1(a)]. Figure 1(b) shows the cross-sectional view of a three-terminal n-channel a-Si:H TFT used in the measurements and model fits.

 

p1147_fig_1

FIGURE 1 — (a) The channel passivated bottom-gate inverted-staggered a-Si:H TFT fabricated at the Flexible Display Center. (b) Cross-sectional view of the reflective (REFL) type a-Si:H TFT with W = 96 μm, L = 9 μm, and fingers = 2.

 


Single-cell-gap transflective liquid-crystal display using double- and single-mode approaches

Peizhi Xu
Hin-yu Mak (SID Student Member)
Tao Du (SID Student Member)
Vladimir G. Chigrinov (SID Fellow)
Hoi-Sing Kwok (SID Fellow)

Hong Kong University ofScience and Technology

Abstract — In this paper, many popular methods to study transflective liquid-crystal-displays (LCDs) have been discussed, and several new transflective LCD configurations with a single cell gap have been proposed. The traditional double-cell-gap method gives the best match of the transmittance/reflectance voltage curve (TVC/RVC) and also the widest viewing angle, but also brings the highest fabrication complexity. The single-cell-gap transflective LCD is much easier to fabricate and also shows a good match of TVC/RVC. A new methodology has been shown to find optimal configurations for single-cell-gap transflective LCDs. New configurations using multimode in a single pixel include twisted-nematic (TN) optically compensated bend (OCB), TN electrically controlled birefringence (ECB), and TN low-twisted nematic (LTN). TN and hybrid-aligned nematic (HAN) modes have been investigated for single-mode transflective LCDs. The results exhibit high contrast ratio, a good match of TVC/RVC, as well as wide viewing angle.

Figure 17 shows the schematic diagram of the HAN-mode transflective LCD. The top and bottom substrates are antiparallel rubbed. Horizontal polyimide is spin-coated on the top substrate during preparation, while vertical polyimide is on the spin-coated bottom substrate. The LC molecules are parallel aligned at the top substrate with a preferred tilt angle of about 2°. The preferred tilt angle of the LC molecules at the bottom substrate is around 88°. An ordinary polarizer coated with an anti-reflection layer is used for both transmissive and reflective regions to improve the dark-state performance.

 

p1163_fig_17

FIGURE 17 — Scheme of the transflective LCD: reflective part and transmissive part, HAN mode.

 


A touch-sensitive display with embedded hydrogenated amorphous-silicon photodetector arrays

Hyun-Sang Park (SID Student Member)
Tae-Jun Ha (SID Student Member)
Yongtaek Hong (SID Member)
Jae-Hoon Lee
Byoung-Jun Lee
Bong-Hyun You (SID Member)
Nam-Deog Kim (SID Member)
Min-Koo Han

Seoul National University

Abstract — A new touch-sensitive hydrogenated amorphous-silicon (a-Si:H) display with embedded optical sensor arrays is presented. The touch-panel operation was successfully demonstrated by fabricating a prototype of a 16-in. active-matrix liquid-crystal display (AMLCD). The proposed system, obviating the need for the extraction of information from the captured images in real time, provides the location of the finger touch. Due to the simple architecture of the system, the touch-panel operation can be readily integrated within large-area displays.

An a-Si:H TFT with an etch-back structure on a glass substrate was fabricated by employing a standard commercial process in order to investigate the possibility of using the a-Si:H device as a photosensitive element. After a 250-nm-thick gate metal layer (Mo/AlNd) was sputter deposited and patterned on the glass substrate, a 450-nm-thick silicon nitride (SiNx) layer as a gate insulator, a 200-nm-thick a-Si:H film and a 50-nm-thick n+ silicon layer were deposited by PECVD at 400°C without breaking vacuum.

 

p1168_fig_6

FIGURE 6 — The micrographs of the unit pixel in the fabricated AMLCD panel.

 


New driving scheme for intelligent power-efficient high-voltage display drivers

Ann Monté
Pieter Bauwens
Stefaan Maeyaert
Jan Doutreloigne

University of Ghent

Abstract — A new bistable-display driver is presented. The innovation in the developed driver is the addition of a new logical block that calculates the most energy-efficient driving waveforms. In this paper, the algorithms being applied to the row and column waveforms in order to reduce the power consumption are discussed. Some theoretical as well as experimental results are shown, proving a reduction in the power consumption by about 50%. The proposed algorithms are especially important for battery-powered applications.

By short-circuiting row i and row (i + 1) for a short period of time, before making the transition from one voltage level to the other, part of the otherwise wasted charge can be recuperated. Row i and row (i + 1) are charged to 20 V when both rows, which were at 40 V and 0 V are short-circuited, respectively. As a result, the voltage source only has to deliver the power needed to increase the voltage level of row (i +1) from 20 to 40 V and not from 0 to 40 V, implying a big power savings. This principle is demonstrated in Fig. 3.

 

p1173_fig_3

FIGURE 3 — Charge recycling by short-circuiting rows.