Challenge: a large amount of work is required to clean digitized books for NLP analysis because of errors in the scanned text and duplicate volumes in the corpora.
Approach: They propose methods to handle optical character recognition errors in scanned texts . they identify the canonical version for each of 17,136 repeatedly-scanned books .
Outcome: The proposed method corrects over six times as many errors as it introduces, the authors show . the authors evaluate a collection of 19,347 texts from the Gutenberg dataset and 96,635 from the HathiTrust Library .

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Low-resource Post Processing of Noisy OCR Output for Historical Corpus Digitisation (L18-1)

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Challenge: 7.6% of the words in the original OCR text contain an error; fully manual correction would take thousands of hours due to the size of the corpus.
Approach: They propose a post-processing system to efficiently correct OCR errors in a 2.7 million word Faroese corpus.
Outcome: The proposed method reduces the word error rate to 1.3% with around 65 hours of human annotator work.
OCR Post Correction for Endangered Language Texts (2020.emnlp-main)

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Challenge: Currently, there is little to no data available to build natural language processing models for endangered languages.
Approach: They propose a benchmark dataset of transcriptions for scanned books in three critically endangered languages and a method to improve OCR in these data-scarce settings.
Outcome: The proposed method reduces the recognition error rate by 34% across the three endangered languages.
Neural OCR Post-Hoc Correction of Historical Corpora (2021.tacl-1)

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Challenge: Optical character recognition (OCR) is crucial for a deeper access to historical collections.
Approach: They propose a neural approach based on a combination of recurrent (RNN) and deep convolutional network (ConvNet) to correct OCR transcription errors.
Outcome: The proposed model reduces the word error rate of 32.3% by more than 89% on a historical book corpus in German language.
Unsupervised Multi-View Post-OCR Error Correction With Language Models (2021.emnlp-main)

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Challenge: Prior work used text generation techniques or redundancy in similar passages for OCR error correction, which is not appropriate in cases of low corpus redundancies or weak document contextual information.
Approach: They propose to use a pretrained language model to reconcile different OCR views in unsupervised way so that their combination contains fewer errors than each individual view.
Outcome: The proposed model can reconcile multiple OCR views so that their combined version contains fewer errors than the best OCR view.
Correction of OCR Word Segmentation Errors in Articles from the ACL Collection through Neural Machine Translation Methods (L18-1)

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Challenge: Optical Character Recognition (OCR) can produce a range of errors depending on the quality of the original document.
Approach: They applied a sequence-to-sequence machine translation system to correct word-single-word OCR errors in scientific texts from the ACL collection with an estimated precision and recall above 0.95 on test data.
Outcome: The proposed system corrects word-segmentation OCR errors with an estimated precision and recall above 0.95 on test data.
A Benchmark and Dataset for Post-OCR text correction in Sanskrit (2022.findings-emnlp)

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Challenge: Sanskrit is a classical language with 30 million manuscripts available for digitisation . however, it is considered to be low-resource when it comes to available digital resources.
Approach: They propose to use a post-OCR text correction dataset to correct errors from OCR predictions from 30 different books in the Indian subcontinent.
Outcome: The proposed model outperforms OCR models on graphemic and lexical levels and shows that it is more accurate than previous models.
PreP-OCR: A Complete Pipeline for Document Image Restoration and Enhanced OCR Accuracy (2025.acl-long)

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Challenge: Existing pipelines that combine document image restoration with semantic-aware post-OCR correction can improve text extraction from degraded images.
Approach: They propose a two-stage pipeline that combines document image restoration with semantic-aware post-OCR correction to enhance both visual clarity and textual consistency.
Outcome: The proposed pipeline reduces character error rates by 63.9-70.3% on 13,831 pages of real historical documents in English, French, and Spanish compared to OCR on raw images.
Multi-Input Attention for Unsupervised OCR Correction (P18-1)

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Challenge: Existing methods for OCR correction are mostly supervised methods that correct recognition errors in a single output.
Approach: They propose a sequence-to-sequence model with attention and a decoder with attention averaging to search for consensus among multiple sequences.
Outcome: The proposed methods cut the character and word error rates nearly in half on single inputs and can rival supervised methods.
How Much Data Do You Need? About the Creation of a Ground Truth for Black Letter and the Effectiveness of Neural OCR (2020.lrec-1)

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Challenge: Recent advances in Optical Character Recognition and Handwritten Text Recognition have led to more accurate text recognition of historical documents.
Approach: They propose to build a ground truth for a German-language newspaper published in black letter . they also evaluate the performance of different OCR engines and estimate how much data is needed to achieve high-quality OCR results.
Outcome: The proposed model can recognise black letter text and performs well on data they have not seen during training.
Lexically Aware Semi-Supervised Learning for OCR Post-Correction (2021.tacl-1)

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Challenge: Existing methods for digitizing text in endangered languages rely on manual data curated by the user.
Approach: They propose a semi-supervised learning method that utilizes raw images to improve performance.
Outcome: The proposed method reduces errors by 15%–29% on four endangered languages.

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