tesseract-ocr with --visible-pdf-image
This is a modified version of Tesseract. The official upstream project is here: https://github.com/tesseract-ocr/tesseract
Dependencies:
- leptonica: (tested with leptonica 1.82.0)
The modifications in the visible_pdf_image branch enable the user to input both a "cleaned" image to be used for OCR and a "visible" image that is used in the output PDF. Cleaning an image helps OCR engines by removing background colors and patterns, sharpening text, increasing contrast, etc. The process usually makes the image look terrible to humans, so the idea with this fork is to give us the best of both worlds. This is very useful for digitizing documents.
To clean an image for OCR, try using textcleaner from Fred's ImageMagick Scripts: http://www.fmwconcepts.com/imagemagick/textcleaner/
For the visible image, you can use a compressed version to save space. The only requirement is that the dimensions of the "cleaned" and "visible" images are the same.
Once you've built the visible_pdf_image branch along with the other Tesseract dependencies, just add --visible-pdf-image <image> to the arguments. For example:
tesseract -l eng --visible-pdf-image compressed.webp cleaned.pnm out pdf
Here's the original feature request upstream: tesseract-ocr#210
Tesseract OCR
tesseract-ocr with visible_pdf_image
This is a modified version of Tesseract. The official upstream project is here: https://github.com/tesseract-ocr/tesseract
Dependencies:
- leptonica: This branch works with leptonica 1.79.0. Some APIs were deprecated in versions after 1.80.0.
The modifications in the visible_pdf_image branch enable the user to input both a "cleaned" image to be used for OCR and a "visible" image that the user will see in the output PDF. Cleaning an image helps OCR engines by removing background colors and patterns, sharpening text, increasing contrast, etc. The process usually makes the image look terrible to humans, so the idea with these patches is to give us the best of both worlds.
To clean an image for OCR, I suggest using textcleaner from Fred's ImageMagick Scripts: http://www.fmwconcepts.com/imagemagick/textcleaner/
For the visible image you can use the original copy, but I suggest using a compressed version instead to save space. The only requirement is that the dimensions of the "cleaned" and "visible" images are the same.
Once you've built the visible_pdf_image branch along with the other Tesseract dependencies, just add --visible-pdf-image <image> to the arguments. For example:
tesseract -l eng --visible-pdf-image compressed.webp cleaned.pnm out pdf
I've found this to be very helpful when creating searchable PDFs from scanned documents, receipts, etc. YMMV. Here's the original feature request upstream: tesseract-ocr#210
Table of Contents
About
This package contains an OCR engine - libtesseract and a command line program - tesseract.
Tesseract 4 adds a new neural net (LSTM) based OCR engine which is focused on line recognition, but also still supports the legacy Tesseract OCR engine of Tesseract 3 which works by recognizing character patterns. Compatibility with Tesseract 3 is enabled by using the Legacy OCR Engine mode (--oem 0). It also needs traineddata files which support the legacy engine, for example those from the tessdata repository.
Important Notes
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Stefan Weil is the current lead developer. Ray Smith was the lead developer until 2018. The maintainer is Zdenko Podobny. For a list of contributors see AUTHORS and GitHub's log of contributors.
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Tesseract has unicode (UTF-8) support, and can recognize more than 100 languages "out of the box".
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Tesseract supports various image formats including PNG, JPEG and TIFF.
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Tesseract supports various output formats: plain text, hOCR (HTML), PDF, invisible-text-only PDF, TSV and ALTO (the last one - since version 4.1.0).
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You should note that in many cases, in order to get better OCR results, you'll need to improve the quality of the image you are giving Tesseract.
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This project does not include a GUI application. If you need one, please see the 3rdParty documentation.
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Tesseract can be trained to recognize other languages. See Tesseract Training for more information.
Brief history
Tesseract was originally developed at Hewlett-Packard Laboratories Bristol UK and at Hewlett-Packard Co, Greeley Colorado USA between 1985 and 1994, with some more changes made in 1996 to port to Windows, and some C++izing in 1998. In 2005 Tesseract was open sourced by HP. From 2006 until November 2018 it was developed by Google.
Major version 5 is the current stable version and started with release 5.0.0 on November 30, 2021. Newer minor versions and bugfix versions are available from GitHub.
Latest source code is available from main branch on GitHub. Open issues can be found in issue tracker, and planning documentation.
See Release Notes and Change Log for more details of the releases.
Installing Tesseract
You can either Install Tesseract via pre-built binary package or build it from source.
A C++ compiler with good C++17 support is required for building Tesseract from source.
Running Tesseract
Basic command line usage:
tesseract imagename outputbase [-l lang] [--oem ocrenginemode] [--psm pagesegmode] [configfiles...]
For more information about the various command line options use tesseract --help or man tesseract.
Examples can be found in the documentation.
For developers
Developers can use libtesseract C or
C++ API to build their own application. If you need bindings to libtesseract for other programming languages, please see the
wrapper section in the AddOns documentation.
Documentation of Tesseract generated from source code by doxygen can be found on tesseract-ocr.github.io.
Support
Before you submit an issue, please review the guidelines for this repository.
For support, first read the documentation, particularly the FAQ to see if your problem is addressed there. If not, search the Tesseract user forum, the Tesseract developer forum and past issues, and if you still can't find what you need, ask for support in the mailing-lists.
Mailing-lists:
- tesseract-ocr - For tesseract users.
- tesseract-dev - For tesseract developers.
Please report an issue only for a bug, not for asking questions.
License
The code in this repository is licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
NOTE: This software depends on other packages that may be licensed under different open source licenses.
Tesseract uses Leptonica library which essentially uses a BSD 2-clause license.
Dependencies
Tesseract uses Leptonica library for opening input images (e.g. not documents like pdf). It is suggested to use leptonica with built-in support for zlib, png and tiff (for multipage tiff).
Latest Version of README
For the latest online version of the README.md see:
https://github.com/tesseract-ocr/tesseract/blob/main/README.md
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