Neural OCR Post-Hoc Correction of Historical Corpora

Lijun Lyu, Maria Koutraki, Martin Krickl, Besnik Fetahu


Abstract
Optical character recognition (OCR) is crucial for a deeper access to historical collections. OCR needs to account for orthographic variations, typefaces, or language evolution (i.e., new letters, word spellings), as the main source of character, word, or word segmentation transcription errors. For digital corpora of historical prints, the errors are further exacerbated due to low scan quality and lack of language standardization. For the task of OCR post-hoc correction, we propose a neural approach based on a combination of recurrent (RNN) and deep convolutional network (ConvNet) to correct OCR transcription errors. At character level we flexibly capture errors, and decode the corrected output based on a novel attention mechanism. Accounting for the input and output similarity, we propose a new loss function that rewards the model’s correcting behavior. Evaluation on a historical book corpus in German language shows that our models are robust in capturing diverse OCR transcription errors and reduce the word error rate of 32.3% by more than 89%.
Anthology ID:
2021.tacl-1.29
Volume:
Transactions of the Association for Computational Linguistics, Volume 9
Month:
Year:
2021
Address:
Cambridge, MA
Editors:
Brian Roark, Ani Nenkova
Venue:
TACL
SIG:
Publisher:
MIT Press
Note:
Pages:
479–493
Language:
URL:
https://aclanthology.org/2021.tacl-1.29
DOI:
10.1162/tacl_a_00379
Bibkey:
Cite (ACL):
Lijun Lyu, Maria Koutraki, Martin Krickl, and Besnik Fetahu. 2021. Neural OCR Post-Hoc Correction of Historical Corpora. Transactions of the Association for Computational Linguistics, 9:479–493.
Cite (Informal):
Neural OCR Post-Hoc Correction of Historical Corpora (Lyu et al., TACL 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.tacl-1.29.pdf
Video:
 https://aclanthology.org/2021.tacl-1.29.mp4