This paper presents a document image thresholding technique that binarizes badly illuminated document images by the photometric correction. Based on the observation that illumination normally varies smoothly and document images often contain a uniformly colored background, the global shading variation is estimated by using a two-dimensional Savitzky-Golay filter that fits a least square polynomial surface to the luminance of a badly illuminated document image. With the knowledge of the global shading variation, shading degradation is then corrected through a compensation process that produces an image with roughly uniform illumination. Badly illuminated document images are accordingly binarized through the global thresholding of the compensated ones. Experiments show that the proposed thresholding technique is fast, robust, and efficient for the binarization of badly illuminated document images.

I have a lot of people to thank for without whom I would not have made this far. I am deeply grateful to my advisor Bob McKeown who has supported me over the past years and brought me into the KamLAND project. His patience, encouragement and wisdom have been guiding me through my Ph.D. study. I own my special thanks to Dan Dwyer for his constant advice and guidance to make this thesis analysis even possible. His knowledge and diligence always set an example for me. I am greatly thankful to Christopher Mauger who had been working together with me since the first day I joined KamLAND, taught me all the techniques in experimental nuclear physics, and helped me going though all the difficulties living in a foreign country, both in the United State and in Japan. I would like to thank my fellow graduate students for all the days we spent together to get the work done. Tommy O’Donnell deserves my many thanks for the countless discussions we had about the analysis. His encouragement is essential to keep me moving on. Greg Keefer and Chris Grant are my kind roommates during my long stays in Japan. Their presences are the only thing that kept me in sane. I would like to thank Kyohei Nakajima, Yuri Shimizu and Yukie Minekawa for always being my accompany in the underground mine, for making my life in Mozumi bearable. I would like to thank all my KamLAND collaborators for their hard work. I thank Atsuto Suziki, Kunio Inoue and Stuart Freedman for leading this experiment to such a success today. Many thanks to the people who had lent me valuable knowledges