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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Modelling image quality for automotive display technologies

Wolf, Dorothee Christine January 2014 (has links)
The aim of this thesis is to link perceived image quality to physical display parameters. This is done in the context of automotive displays. Specialities of automotive display applications like high ambient lighting conditions and the necessity to access information quickly are explained. A summary of readability models relevant to automotive applications is given and the difference between readability and perceived image quality is explained. The methodology chosen to investigate perceived image quality is the Image-Quality-Circle framework by Engeldrum (2000). Engeldrum states that observers form their image quality rating by weighting the visual attributes they perceive. Visual algorithms, which can be investigated via psychometric scaling, link visual attributes to the underlying physical image parameters which are typically measure by physical instruments. The visual attributes investigated in this thesis are perceived contrast, brightness, blackness and colourfulness. Perceived contrast, brightness and blackness are derived from display luminance via the DICOM just noticeable difference (JND) scale. Colourfulness is scaled based colour gamut in the CIE1931 chromaticity diagram. It was shown that image quality rating rises with growing perceived contrast; the limiting factors are glare and perceived blackness. In colourfulness scaling a linear relationship between colour gamut and colourfulness rating was demonstrated. Higher colourfulness can compensate lower brightness in perceived image quality.
2

Photo-alignment Effect in Liquid Crystal Film Doped with Nanoparticles and Azo-dye

Chen, Wen-zheng 18 July 2009 (has links)
This work discusses the effect of photo-alignment in a liquid-crystal film that is doped with nanoparticles and azo-dye. The vertical alignment that is induced by nanoparticles of polyhedral oligomeric silsesquioxanes can be changed into homogeneous alignment by the absorption of photo-excited azo-dye. Both electro-optical and surface properties are analyzed to confirm this phenomenon. An electrically tunable polarization-dependent LC phase grating is produced using the method. By this method, we also present a transflective liquid crystal display with a single cell-gap in a dual-alignment configuration. This dual structure was fabricated via a single-step laser-light exposure through a photomask. The vertical alignment induced by nanoparticles of polyhedral oligomeric silsesquioxanes can be changed into a homogeneous alignment via absorption of photo-excited azo dye. The LC molecules at the transmissive and reflective pixels are homogeneous and hybrid alignment, respectively, at which optimal phase retardations of half and quarter wavelengths are achieved. Both nanoparticle- and azo-dye-induced vertical and homogeneous alignments are non-contact alignment processes and have potential for practical application.
3

High-efficiency Blue Phase Liquid Crystal Displays

Li, Yan 01 January 2012 (has links)
Blue phase liquid crystals (BPLCs) have a delicate lattice structure existing between chiral nematic and isotropic phases, with a stable temperature range of about 2 K. But due to short coherent length, these self-assembled nano-structured BPLCs have a fast response time. In the past three decades, the application of BPLC has been rather limited because of its narrow temperature range. In 2002, Kikuchi et al. developed a polymer stabilization method to extend the blue-phase temperature range to more than 60 K. This opens a new gateway for display and photonic applications. In this dissertation, I investigate the material properties of polymer-stabilized BPLCs. According the Gerber’s model, the Kerr constant of a BPLC is linearly proportional to the dielectric anisotropy of the LC host. Therefore, in the frequency domain, the relaxation of the Kerr constant follows the same trend as the dielectric relaxation of the host LC. I have carried out experiments to validate the theoretical predictions, and proposed a model called extended Cole-Cole model to describe the relaxation of the Kerr constant. On the other hand, because of the linear relationship, the Kerr constant should have the same sign as the dielectric anisotropy of the LC host; that is, a positive or negative Kerr constant results from positive (∆ε > 0) or negative host LCs (∆ε < 0), respectively. BPLCs with a positive Kerr constant have been studied extensively, but there has been no study on negative ∆ε polymer-stabilized BPLCs. Therefore, I have prepared a BPLC mixture using a negative ∆ε LC host and investigated its electro-optic properties. I have demonstrated that indeed the induced birefringence and Kerr constant are of negative sign. Due to the fast response time of BPLCs, color sequential display is made possible without color breakup. By removing the spatial color filters, the optical efficiency and resolution density are both tripled. With other advantages such as alignment free and wide viewing angle, polymer-stabilized BPLC is emerging as a promising candidate for next-generation displays. However, the optical efficiency of the BPLC cell is relatively low and the operating voltage is quite high using conventional in-plane-switching electrodes. I have proposed several device structures for improving the optical efficiency of transmissive BPLC cells. Significant improvement in transmittance is achieved by using enhanced protrusion electrodes, and a 100% transmittance is achievable using complementary enhanced protrusion electrode structure. For a conventional transmissive blue phase LCD, although it has superb performances indoor, when exposed to strong sunlight the displayed images could be washed out, leading to a degraded contrast ratio and readability. To overcome the sunlight readability problem, a common approach is to adaptively boost the backlight intensity, but the tradeoff is in the increased power consumption. Here, I have proposed a transflective blue phase LCD where the backlight is turned on in dark surroundings while ambient light is used to illuminate the displayed images in bright surroundings. Therefore, a good contrast ratio is preserved even for a strong ambient. I have proposed two transflective blue phase LCD structures, both of which have single cell gap, single gamma driving, reasonably wide view angle, low power consumption, and high optical efficiency. Among all the 3D technologies, integral imaging is an attractive approach due to its high efficiency and real image depth. However, the optimum observation distance should be adjusted as the displayed image depth changes. This requires a fast focal length change of an adaptive lens array. BPLC adaptive lenses are a good candidate because of their intrinsic fast response time. I have proposed several BPLC lens structures which are polarization independent and exhibit a parabolic phase profile in addition to fast response time. To meet the low power consumption requirement set by Energy Star, high optical efficiency is among the top lists of next-generation LCDs. In this dissertation, I have demonstrated some new device structures for improving the optical efficiency of a polymerstabilized BPLC transmissive display and proposed sunlight readable transflective blue-phase LCDs by utilizing ambient light to reduce the power consumption. Moreover, we have proposed several blue-phase LC adaptive lenses for high efficiency 3D displays.

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