dc.description.abstract | 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. | en_US |