電泳式顯示器之影像再現技術;Image reproduction techniques for electrophoretic displays

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題名:	電泳式顯示器之影像再現技術;Image reproduction techniques for electrophoretic displays
作者:	楊長暻;Yang,Chang-jing
貢獻者:	通訊工程學系
關鍵詞:	多線式驅動;電泳式顯示器;驅動波形;drving waveform;electrophoretic display;EPD;MLA;multiline addressing
日期:	2013-04-21
上傳時間:	2013-06-19 15:24:43 (UTC+8)
出版者:	國立中央大學
摘要:	近年來，紙本書籍的閱讀習慣逐漸被電子閱讀器所取代，以電泳式顯示器作為顯示的電子書閱讀器具有幾個特點，首先，電泳式顯示器是反射式的顯示器，相較於穿透式顯示器(如液晶顯示器)，電泳式顯示器其反射日光的觀看模式讓閱讀者的眼睛感到較為舒適，並且擁有寬廣的視角。其次，電泳式顯示器是雙穩態的顯示器，當閱讀器沒有電力供給時可以維持畫面，僅在更換畫面時才需供給電力。然而，除了上述優點，電泳式顯示器同時也具有下列缺點，首先，由於電泳式顯示器的顯像粒子反應時間長於數個微秒，導致畫面更換速度慢。其次，單色的電泳式顯示器的對比度低於10，裝置彩色濾光片後的彩色電泳式顯示器僅能顯示小部分標準RGB色彩空間(sRGB)，因而導致影像的畫面品質不佳。本論文以三個章節探討電泳式顯示器影像再現之問題與其解決方法。第二章首先以不同的脈波調變方式分別驅動電泳式顯示器，並量測分析其反射率。我們提出一種程式化驅動波形設計方法，以減低該顯示器之影像更新時間。接著討論基於其電泳式顯示器顯像粒子帶電量之驅動波形設計，顯像粒子之充電機制由摩擦充電及接觸充電構成，於驅動該顯示器時，由驅動波形之區間完成顯像粒子之的充電。我們提出一種驅動波形之設計方法，讓顯像粒子保持在適宜的帶電量，使得電泳式顯示器達到較佳之反射率。本章最後討論電泳式顯示器的影像雜訊，經分析為不均勻的顯像粒子分佈而導致，我們提出影像補償系統以改善影像雜訊的問題。第三章提出以多線式演算法應用於驅動電泳式顯示器以達到提升更新畫面速度的優點。然而，由於電泳式顯示器的光電反應為非線性，以非負矩陣分解法(nonnegative matrix factorization)產生的矩陣為數位驅動信號時，再現影像將產生大量的雜訊。因此，我們提出適用於電泳式顯示器的無損失多線式驅動演算法，此演算法非但提升更新畫面速度同時亦可改善其再現影像的雜訊。第四章討論彩色影像再現於電泳式顯示器的問題與解決方法。針對電泳式顯示器對比度不足而產生之色彩不匹配及假輪廓問題，提出結合色彩對應方法與後抖動方法，可達到改善電泳式顯示器假輪廓現象與增加影像重現之對比度。由各章節實驗結果可以發現，我們所提出的方法皆可以有效改善電泳式顯示器之再現影像品質與提升畫面更新速度。In recent years, electronic readers have gradually replaced hard copies of books in the consumer market. Electrophoretic displays (EPDs) have become popular candidates used for the display of electronic readers because of several superior features. First, they are reflective displays, which are more comforTable to read on than transmissive displays. Second, they are bisTable, in that an image can be maintained on the observing surface when power is not being supplied. Power is only consumed when an image is being refreshed. However, several issues should be solved. First, the contrast ratios of the optical reflectance of monochromatic EPDs are less than 10. The color gamut of EPDs equipped with color filter is much lower than that of standard RGB (sRGB) color space. This may lead to a poor image reproduction quality because of the low image contrast. Second, the response time of pigment particle of EPDs is longer than several tens of milliseconds. This may leads to a slow image refreshing rate. This dissertation has three Chapters to discuss the problems and solutions related to the reproduction of images on electrophoretic displays (EPDs). In Chapter 2, the electro-optical response of EPDs has been analyzed when the driver uses different pulse modulation schemes. We proposed a programmed driving waveform and a design process to speed up the image-updating rate of an EPD. Driving waveforms based on the particle charge of EPDs are investigated. The charging mechanisms of contact charging and triboelectric charging determine the particle charge of EPDs. Driving waveforms containing both charging mechanisms are proposed for driving EPDs. In addition, we discuss the image noises on EPDs. Nonuniform optical response and powder clustering become visible when an observer is moving close to the image. We proposed an image compensation system to mitigate the nonuniformity on an EPD. In Chapter 3, multiline addressing (MLA) schemes for EPDs have been developed for improving the driving efficiency. Compared with the conventional row-by-row scheme, MLA is observed to improve the image refreshing rate by lowering the rank of the basis matrix. Since the electro-optical response of an EPD is not a linear curve, the MLA scheme using nonnegative matrix factorization (NMF) produces a noisy image on EPDs. Therefore, we have proposed a lossless matrix factorization (LMF) method. The MLA scheme using LMF not only improves the image refreshing rate but also shows images without noise.In Chapter 4, we discuss the problems and solutions related to the reproduction of color images on EPDs. A novel system consisting of a post-dithering algorithm and a hybrid gamut mapping algorithm is proposed to deal with false contouring and gamut mismatches, respectively. The proposed system mitigates the false contouring and increases the contrast in images. The experimental results in each Chapter show that our proposed methods improve image reproduction quality and speed up the image-updating rate of EPDs.
顯示於類別:	[通訊工程研究所] 博碩士論文

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