Minkoo Kim

Liquid crystal displays with temperature-independent characteristics

A new technology is presented that enables liquid crystal displays (LCDs) to have temperature-independent characteristics. This work shows how severely the color image quality of LCDs is affected by the ambient temperature change in addition to showing how the ambient temperature considerably affects the motion image quality of overdriven LCDs. Transmittance-voltage curve-shifting technology is proposed to compensate for the color change owing to temperature change. This new technology reduces a half-maximum luminance error from 24% to 6% over the temperature range from 0°C to 50°C. The linear overdrive (OD) technology over the wide temperature is presented to overcome the temperature-dependent characteristics of LCDs. With this technique, the distribution of the OD error is reduced by 65%. The color and motion image quality of LCDs can be kept the same with these techniques, regardless of temperature.

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.

Time-dependent color simulation of active-matrix liquid crystal display adopting the field sequential driving method

Abstract A time-dependent display color simulation method is proposed. For the time-dependent simulation, we applied our behavioral model of liquid crystals (LC). The model provides the transient response characteristics of the LC. The color simulation of a twisted nematic active matrix liquid crystal display (AMLCD) adopting a field sequential (FS) driving method is possible when combining the transient LC responses with periodically operating red-greenblue (RGB) light emitting diodes (LEDs). By modifying the gate start pulse of the conventional AMLCD, we created a virtual AMLCD driven by the FS method. The color performance of the panel was measured at five vertical positions, and the results showed that the RGB LEDs should be driven by a 70% duty parameter and a 50% shifting parameter to minimize line-to-line color characteristic deviations in the AMLCD panel. By using the proposed simulation method, it is possible to find the optimal FS driving condition for any display with arbitrary response characteristics to exhibit the best color performance.

Overdrive technology compensating for ambient temperature

Abstract. We propose an overdrive (OD) technology to precisely compensate for the temperature-dependent response characteristics of liquid-crystal displays (LCDs). The optical responses of LCDs are highly dependent on ambient temperature. After analyzing the optimized OD values, the new OD technology uses simple calculation logic instead of bulky OD lookup tables to obtain OD values of rising transitions over a wide range of ambient temperatures. We also show that it is possible to automatically adjust the optimum OD values depending on the ambient temperature. The results show that the proposed OD technology can improve motion image quality without any motion artifacts regardless of the ambient temperature. We expect that our proposed OD technology will ensure that LCD products have a consistent motion image quality regardless of the ambient temperature without any increase in cost.

Perceptually Reduced Crosstalk by Modifying Binocular Images Depending on Dominant Eye

We propose a new method that uses ocular dominance to reduce perceived crosstalk in autostereoscopic 3D displays. When one increases the brightness of dominant eyes view while decreasing the other, the crosstalk effectively decreases for the dominant eye but increases for the other. We hypothesize that such manipulation would reduce the perceived crosstalk because the brains visual processing relies more on the dominant eye than the other. We verify our hypothesis through a psychophysical experiment.

Amendment of CIECAM02 with a technical extension to compensate Helmholtz-Kohlrausch effect for chromatic characterization of display devices

Abstract This paper proposes a method of compensating for the Helmholtz-Kohlrausch (H-K) effect which is a factor not being concerned in CIECAM02. H-K effect refers to the color appearance phenomenon that colored light appears brighter than achromatic light of the same luminance. By the magnitude estimation method, the perceptual lightness of active matrix liquid crystal display (AMLCD) is investigated. The results show that the lightness values predicted by CIECAM02 are lower than perceptual lightness values evaluated by the psychophysical experiments because of the H-K effect. The results on MobileCAM-v2, which is a refined version of CIECAM02, are investigated, as well. Since the color gamut of the display has been widening, the compensation for the H-K effect has also been increasingly important. In this paper, the method to compensate for the H-K effect in CIECAM02 is proposed. By modifying Fairchild’s equation, which is previously announced for CIELAB, CIECAM02 can be developed as a more complete color appearance model that can be universally applied to the display devices having a wide color gamut.

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.