A new pre-classification method based on associative matching method

Yutaka Katsuyama*, Akihiro Minagawa, Yoshinobu Hotta, Shinichiro Omachi, Nei Kato

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)


Reducing the time complexity of character matching is critical to the development of efficient Japanese Optical Character Recognition (OCR) systems. To shorten processing time, recognition is usually split into separate preclassification and recognition stages. For high overall recognition performance, the pre-classification stage must both have very high classification accuracy and return only a small number of putative character categories for further processing. Furthermore, for any practical system, the speed of the pre-classification stage is also critical. The associative matching (AM) method has often been used for fast pre-classification, because its use of a hash table and reliance solely on logical bit operations to select categories makes it highly efficient. However, redundant certain level of redundancy exists in the hash table because it is constructed using only the minimum and maximum values of the data on each axis and therefore does not take account of the distribution of the data. We propose a modified associative matching method that satisfies the performance criteria described above but in a fraction of the time by modifying the hash table to reflect the underlying distribution of training characters. Furthermore, we show that our approach outperforms pre-classification by clustering, ANN and conventional AM in terms of classification accuracy, discriminative power and speed. Compared to conventional associative matching, the proposed approach results in a 47% reduction in total processing time across an evaluation test set comprising 116,528 Japanese character images.

Original languageEnglish
Title of host publicationProceedings of SPIE-IS and T Electronic Imaging - Document Recognition and Retrieval XVII
Publication statusPublished - 2010
Externally publishedYes
EventDocument Recognition and Retrieval XVII - San Jose, CA, United States
Duration: 2010 Jan 192010 Jan 21

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceDocument Recognition and Retrieval XVII
Country/TerritoryUnited States
CitySan Jose, CA


  • Associative matching method
  • Clustering
  • Hash table
  • OCR
  • Pre-classification

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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