State Of The Art

As discussed in the previous chapter, the PrIx framework explicitly adopts the IR point of view, but it draws from many concepts and methods developed over the last 50 years in the field ofKWS, first for speech signals and more recently for text images. A comprehensive survey of these approaches can be consulted in [23] and a recent review in [36]. This chapter overviews the taxonomy and the most important state-of-the-art approaches to KWS for text images. Detailed insights about the most interesting and/or relevant of these approaches will be provided in Chapter 7 of this book. This chapter also reviews the works carried out so far on certain issues which are very significant for PrIx (and KWS alike) but which are very seldom considered in the KWS literature; namely querying text images for hyphenated, abbreviated and/or multiple words. Finally, since PrIx shares optical and language models with HTR, the state of the art in HTR is also briefly outlined.