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  • Disputation: 2020-09-03 13:15 J1630, Karlskrona
    Westphal, Florian
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datavetenskap.
    Data and Time Efficient Historical Document Analysis2020Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Over the last decades companies and government institutions have gathered vast collections of images of historical handwritten documents. In order to make these collections truly useful to the broader public, images suffering from degradations, such as faded ink, bleed through or stains, need to be made readable and the collections as a whole need to be made searchable. Readability can be achieved by separating text foreground from page background using document image binarization, while searchability by search string or by example image can be achieved through word spotting. Developing algorithms with reasonable binarization or word spotting performance is a difficult task. Additional challenges are to make these algorithms execute fast enough to process vast collections of images in a reasonable amount of time, and to enable them to learn from few labeled training samples. In this thesis, we explore heterogeneous computing, parameter prediction, and enhanced throughput as ways to reduce the execution time of document image binarization algorithms. We find that parameter prediction and mapping a heuristics based binarization algorithm to the GPU lead to an 1.7 and 3.5 increase in execution performance respectively. Furthermore, we identify for a learning based binarization algorithm using recurrent neural networks the number of pixels processed at once as way to trade off execution time with binarization quality. The achieved increase in throughput results in a 3.8 times faster overall execution time. Additionally, we explore guided machine learning (gML) as a possible approach to reduce the required amount of training data for learning based algorithms for binarization, character recognition and word spotting. We propose an initial gML system for binarization, which allows a user to improve an algorithm’s binarization quality by selecting suitable training samples. Based on this system, we identify and pursue three different directions, viz., formulation of a clear definition of gML, identification of an efficient knowledge transfer mechanism from user to learner, and automation of sample selection. We explore the Learning Using Privileged Information paradigm as a possible knowledge transfer mechanism by using character graphs as privileged information for training a neural network based character recognizer. Furthermore, we show that, given a suitable word image representation, automatic sample selection can help to reduce the amount of training data required for word spotting by up to 69%.

  • Disputation: 2020-09-16 14:00 Dallora Moraes, Ana Luiza
    Machine learning applications in healthcare2020Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)