Tesseract OCR Engine
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This document provides an overview of the Tesseract OCR engine, including a brief history of OCR technology, details about Tesseract's development and architecture, and announcements about version 2.00. It describes how Tesseract uses techniques like text line finding, baseline approximation, and static/adaptive classifiers to recognize words despite challenges with spacing, italics, and other font variations. The document also notes areas where commercial OCR systems may have advantages over Tesseract, such as page layout analysis, language support, and accuracy.
Tesseract OCR Engine
- 2. Contents • Introduction & history of OCR • Tesseract architecture & methods • Announcing Tesseract 2.00 • Training Tesseract • Future enhancements
- 3. A Brief History of OCR • What is Optical Character Recognition? • A Brief History of OCR • OCR predates electronic computers!
- 5. A Brief History of OCR • 1929 – Digit recognition machine • 1953 – Alphanumeric recognition machine • 1965 – US Mail sorting • 1965 – British banking system • 1976 – Kurzweil reading machine • 1985 – Hardware-assisted PC software • 1988 – Software-only PC software • 1994-2000 – Industry consolidation
- 6. Tesseract Background • Developed on HP-UX at HP between 1985 • and 1994 to run in a desktop scanner. • Came neck and neck with Caere and XIS • in the 1995 UNLV test. • (See http://www.isri.unlv.edu/downloads/AT-1995.pdf ) • Never used in an HP product. • Open sourced in 2005. Now on: • http://code.google.com/p/tesseract-ocr • Highly portable.
- 7. Tesseract OCR Architecture • Baselines are rarely perfectly straight • Text Line Finding – skew independent – • published at ICDAR’95 Montreal. • (http://scholar.google.com/scholar?q=skew+detection+smith) • Baselines are approximated by quadratic splines • to account for skew and curl. • Meanline, ascender and descender lines are a • constant displacement from baseline. • Critical value is the x-height.
- 8. Spaces between words are tricky too • Italics, digits, punctuation all create special-case font-dependent spacing. • • Fully justified text in narrow columns can have vastly varying spacing on different lines. • Tesseract: Recognize Word • Outline Approximation • Polygonal approximation is a double-edged sword. • Noise and some pertinent information are both lost.
- 9. Tesseract: Features and Matching • Static classifier uses outline fragments as features. Broken characters are easily recognizable by a small->large matching process in classifier. (This is slow.) • Adaptive classifier uses the same technique! • (Apart from normalization method)
- 10. Announcing tesseract-2.00 • Fully Unicode (UTF-8) capable • Already trained for 6 Latin-based • languages (Eng, Fra, Ita, Deu, Spa, Nld) • Code and documented process to train at • http://code.google.com/p/tesseract-ocr • UNLV regression test framework • Other minor fixes
- 11. Commercial OCR v Tesseract • Page layout analysis. • More languages. • Improve accuracy. • Add a UI.