Seung-Ryeol Kim

Optimum display luminance dependence on ambient illuminance

Abstract. Viewing high luminance displays under low light conditions causes unbearable glare. On the other hand, viewing low luminance displays under bright light conditions reduces visibility. We investigate the comfortable display luminance range for several different conditions of ambient illuminance through a psychophysical experiment, which involved 30 subjects. The obtained upper (lower) limits of the comfortable zone were 516 (113), 574 (116), 612 (130), 664 (154), 737 (177), 790 (204), and 836 (246)  cd/m2, for ambient illuminances of 50, 100, 200, 500, 1000, 2000, and 5000 lx, respectively.

Driving technology for improving motion quality of active-matrix organic light-emitting diode display

Abstract. This paper reports transient response characteristics of active-matrix organic light emitting diode (AMOLED) displays for mobile applications. This work reports that the rising responses look like saw-tooth waveform and are not always faster than those of liquid crystal displays. Thus, a driving technology is proposed to improve the rising transient responses of AMOLED based on the overdrive (OD) technology. We modified the OD technology by combining it with a dithering method because the conventional OD method cannot successfully enhance all the rising responses. Our method can improve all the transitions of AMOLED without modifying the conventional gamma architecture of drivers. A new artifact is found when OD is applied to certain transitions. We propose an optimum OD selection method to mitigate the artifact. The implementation results show the proposed technology can successfully improve motion quality of scrolling texts as well as moving pictures in AMOLED displays.

Auto-brightness control technology depending on user’s pupil area

An ambient illuminance sensor of a mobile device does not always accurately measure the light that directly affects human perception of the display brightness. Thus, viewing high-luminance displays under lowlight conditions causes an unbearable glare, while viewing low-luminance displays under bright-light conditions causes very poor visibility. In this paper, an automatic brightness control (ABC) technology depending on pupil area is proposed. The experimental results revealed that the pupil area decreases by 33% as the ambient illuminance increases tenfold. A linear relation was also observed between appropriate display luminance and logarithm of ambient illuminance in our previous investigation. As a result, the comfortable display luminance is proportional to the relative pupil area, which enables us to propose a novel ABC technology depending on the pupil area.

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

Abstract 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 Ocular Dominance on Touch Position

In this paper, we analyzed the effect of ocular dominance on touch positions when users touched a three-dimensional (3D) object on a two-dimensional (2D) touch panel while watching a 3D display. We performed a psychophysical experiment where eight subjects (four right-eye-dominant and four left-eyedominant) participated. When touching 3D objects with uncrossed disparities, touch positions were mainly influenced by ocular dominance and depth of the 3D image (P <; 10-189). For crossed disparities, touch positions were mainly influenced by ocular dominance (P <; 10-18). However, the depth of the 3D image had no significant effect on touch positions (P = 0.783). Our findings can help to design more accurate and comfortable interfaces for 3D systems with touch feedback.

Adaptive charge sharing method for liquid crystal displays with lower power consumption

Abstract. This paper proposes an adaptive charge sharing (ACS) method for reducing power consumption in liquid crystal displays (LCDs). Our ACS method involves calculating the power consumption of all data lines assuming the charge is shared and analyzing the analog characteristics of the data transitions. With conventional CS, charge is shared between data lines only when the polarities of data signals change. Our ACS method selectively shares charge even when no polarity change occurs, but only if CS provides an overall reduction in power consumption. To compare the performance of ACS and conventional CS, we applied the ACS method to common inversion methods, namely, column, two-dot, and Z inversion. Our simulation results demonstrate that the ACS method can effectively reduce power consumption, especially with the column and Z inversion methods. The average power consumption of the ACS method with column and Z inversion was 87.7% and 84.7%, respectively, of the conventional CS power consumption.