Improving Color Tracking in In-Plane Switching Mode Liquid-Crystal Displays
- PDF / 431,667 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 211 Views
Improving Color
Tracking in In-Plane Switching Mode Liquid-Crystal Displays
Yuka Utsumi, Shinichi Komura, Ikuo Hiyama, Makoto Tsumura, and Katsumi Kondo Abstract Color tracking describes the ability of a display to faithfully reproduce the color quality of the source image. In liquid-crystal displays (LCDs), color tracking is dependent on brightness. In order to achieve high-performance color reproduction in LCDs, the accuracy of color tracking needs to be improved. By analyzing the characteristics of twisted-nematic (TN) and in-plane switching (IPS) modes of display, the cause of poor color tracking in each mode and the differences in their causes can be clarified. In TN mode displays, both chromaticity and brightness relate to the director configuration, that is, the directional alignment of the rod-like molecules of the liquid crystals, which varies with applied voltage. The ideal IPS LCD, by virtue of its operating principle, theoretically achieves perfect color tracking; however, in actual use, the color tracking is less than optimal due to twist deformation caused by the fixed directors on the alignment layer. Based on our analysis of these phenomena, we propose strategies for improving color tracking in IPS LCDs. Keywords: flat-panel displays, color tracking, in-plane switching mode, liquid-crystal displays (LCDs), twisted-nematic mode.
duction from the actual. In order to achieve high-performance color reproduction in LCDs, the color tracking needs to be improved. In this article, the cause of poor color tracking in LCDs is described, along with strategies for improving it.
Color Tracking in Relation to Display Characteristics Color Tracking in Twisted-Nematic LCDs As just mentioned, when a gray scale is displayed on a twisted-nematic LCD (TN-LCD), the image appears bluish instead of as achromatic shades of gray. In order to analyze this phenomenon and identify its cause, the intrinsic spectra of TN-LCDs were measured using a TN unit cell, in order to eliminate the color-correcting effects of a backlight and color filter. Figure 1 shows the spectra corresponding to several gray-scale and white representations in a TN unit cell. The peak wavelength, which is defined as the wavelength giving the maximum transmittance in each spectrum, shifts toward shorter wavelengths with decreasing brightness. This peak-wavelength shift causes the bluish appearance of the gray scale. The spectrum of the TN mode depends on the retardation value nd, as explained in the following equations: TTN 1 sin2[ (1 u2)1/2/2]/(1 u2), (1) u 2nd/,
(2)
where TTN is the transmittance of the TN cells, d is the thickness of the liquid-crystal layer, n is the refractive index of a liquid crystal, and is the wavelength. As these expressions show, nd determines the
Introduction The market for liquid-crystal displays (LCDs) has been increasing as a result of advances in their performance. In order for LCDs to gain market share in computer monitors, their viewing-angle characteristics have been improved by using such deve
Data Loading...
