Slant rectification in Russian passport OCR system using fast Hough transform
Elena E. Limonova, Pavel V. Bezmaternykh, Dmitry Nikolaev, Vladimir V. Arlazarov · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2017
In this paper, we introduce slant detection method based on Fast Hough Transform calculation and demonstrate its application in industrial system for Russian passports recognition. About 1.5% of this kind of documents appear to be slant or italic. This fact reduces recognition rate, because Optical Recognition Systems are normally designed to process normal fonts. Our method uses Fast Hough Transform to analyse vertical strokes of characters extracted with the help of x-derivative of a text line image. To improve the quality of detector we also introduce field grouping rules. The resulting algorithm allowed to reach high detection quality. Almost all errors of considered approach happen on passports of nonstandard fonts, while slant detector works in appropriate way.