Very High Precision Optical Character Recognition For Clean-Fixed-Sized True Type Characters

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簡嘉慶(Jia-Ching Jian) 查詢紙本館藏

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資訊工程學系

論文名稱

(Very High Precision Optical Character Recognition For Clean-Fixed-Sized True Type Characters)

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摘要(中)

光學文字辨識(OCR)已經是個發展多年的技術，但是現今卻還沒有一個辨識率百分之百的工具。這個問題是因為辨識影像的來源有很多種不同的狀況，例如文字影像的品質、各式各樣的文章排版、不同的語言、千變萬化的字體、大大小小的文字。只要有其中一項變動，就會對辨識率有極大的影響。
本研究是要應用在本實驗室之 Korat 自動化回歸測試系統上，辨識影像的來源是由 Korat 擷取待測系統的螢幕。因為辨識的影像來源是從螢幕截圖，所以影像會是端正、乾淨且無雜訊。基於這個特性，本研究不需要面對一般 OCR 工具會遇到的情況，如影像歪斜和雜訊干擾的問題。但是會面臨到辨視率需要100%的需求，所以即使在市面上有諸多的 OCR 工具的辨識率都有 88%-95%左右，但仍然無法符合實際應用在 Korat 的系統上的要求。
本研究使用樣板比對的方法結合動態規劃的演算法，在所有可能的辨識組合中，比較剩餘的像素總和，以剩餘最小的組合視為最佳解，藉此辨識率 100%。

摘要(英)

Optical Character Recognition has been studied for many years. However, no OCR tools can claim 100% recognition rate because of the variation in image quality, documentation layout, character fonts and sizes. When there are changes in one of them, recognition rate is often greatly impacted.
Korat is an image-based test regression tool developed in our lab. Korat captures the screen image from a system under test. Therefore, the image is clean, no noises, and no rotation. Based on this condition, we do not deal with situations like image noises, which makes OCR a difficult problem in this thesis.
In Korat′s practical applications, nearly 100% recognition rate is often required. So even there are many existing OCR tools with 88-95% recognition rate, they do not meet the requirements of Korat′s practical applications.
In this research, we combine the template matching and dynamic programming algorithm to find the optimal solution with the smallest sum of remaining pixels in all possible combinations of recognition so that the recognition rate could be achieved 100% at nearly.

關鍵字(中)

★ 光學文字辨識
★ 動態規劃

關鍵字(英)

★ OCR
★ Dynamic Programming
★ True Type
★ Korat

論文目次

摘要 i
Abstract ii
Contents iii
List of Figures v
Chapter 1 Introduction 1
1.1 Automated Regression Testing 1
1.2 Practical OCR Precision Requirement of Korat 2
1.3 Problems in Segmentation 3
1.4 OCR by Template Matching and Dynamic Programming 5
Chapter 2 Background and Related Works 6
2.1 Korat [3] 6
2.2 True Type Font 7
2.3 Optical Character Recognition Technology [4][5] 7
2.3.1 Pre-preprocessing [6] 8
2.3.2 Classification 10
2.3.3 Post-processing [13] 12
2.4 Existing OCR Tools 12
2.4.1 Tesseract-OCR[8][9] 12
2.4.2 ABBYY FineReader[10] 12
2.4.3 Adobe Acrobat Pro DC[11] 14
2.5 Template Matching 15
2.6 Dynamic Programming Algorithm 16
Chapter 3 Combine Tm and DP for OCR 19
3.1 Problems Analysis 19
3.2 Image Preprocessing 20
3.3 Classification by Template Matching 20
3.4 The research problems 21
3.5 Solution to deal with influence of boundary pixels 23
3.6 Solution to deal with overlapped problem 23
3.7 Problems in TMM and minimized template 24
3.8 Combination by TMM and DP 25
3.8.1 The optimization problem comes to mind 25
3.8.2 DP to solve the optimization problem 25
Chapter 4 Preparation of Template Data 28
4.1 Preparation 28
4.2 Image Processing in Template Data 28
4.3 Character Display Tool. 29
Chapter 5 Experiment 32
5.1 Description of Test Data 32
5.2 Comparison of Recognition Rate 32
5.3 Special cases 35
5.4 Speed of Recognition 36
5.5 Font Extension 37
5.6 Test Result Description 37
Chapter 6 Conclusion and Future Works 38
Chapter 7 Reference 40

參考文獻

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[11] Adobe. Feature of Adobe Acrobat DC. Available from: https://acrobat.adobe.com/us/en/acrobat/how-to/ocr-software-convert-pdf-to-text.html.
[12] Wiki. Template Matching. Available from: https://en.wikipedia.org/wiki/Template_matching
[13] Y. Bassil, a.M.A., OCR post-processing error correction algorithm using Google’s Online spelling suggestion. Journal of Emerging Trends in Computing and Information Sciences, 2012.
[14] Gupta, G., et al. Document Layout Analysis and Classification and Its Application in OCR. in 2006 10th IEEE International Enterprise Distributed Object Computing Conference Workshops (EDOCW′06). 2006.
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指導教授

鄭永斌(Yung-Pin Cheng)

審核日期

2017-7-24

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