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108 lines
4.9 KiB
Plaintext
108 lines
4.9 KiB
Plaintext
Introduction
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============
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This package contains the Tesseract Open Source OCR Engine.
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Orignally developed at Hewlett Packard Laboratories Bristol and
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at Hewlett Packard Co, Greeley Colorado, all the code
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in this distribution is now licensed under the Apache License:
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** Licensed under the Apache License, Version 2.0 (the "License");
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** you may not use this file except in compliance with the License.
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** You may obtain a copy of the License at
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** http://www.apache.org/licenses/LICENSE-2.0
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** Unless required by applicable law or agreed to in writing, software
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** distributed under the License is distributed on an "AS IS" BASIS,
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** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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** See the License for the specific language governing permissions and
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** limitations under the License.
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Other Dependencies and Licenses:
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================================
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The Aspirin/MIGRAINES system is no longer required.
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Tesseract can also make use of the libtiff library. (www.libtiff.org)
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Without libtiff, Tesseract can only read uncompressed and G3 compressed
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TIFF files.
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History:
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========
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The engine was developed at Hewlett Packard Laboratories Bristol and
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at Hewlett Packard Co, Greeley Colorado between 1985 and 1994, with some
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more changes made in 1996 to port to Windows, and some C++izing in 1998.
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A lot of the code was written in C, and then some more was written in C++.
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Since then all the code has been converted to at least compile with a C++
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compiler. Currently it builds under Linux with gcc2.95 and under Windows
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with VC++6. The C++ code makes heavy use of a list system using macros.
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This predates stl, was portable before stl, and is more efficent than stl
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lists, but has the big negative that if you do get a segmentation violation,
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it is hard to debug. Another "feature" of the C/C++ split is that the C++
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data structures get converted to C data structures to call the low-level C
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code. This is ugly, and the C++izing of the C code is a step towards
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eliminating the conversion, but it has not happened yet.
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Directory Structure (ordered by dependency):
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============================================
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ccmain Top-level code. The main program resides in tesseractmain.cpp.
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display An "editor" to view and operate on the internal structures.
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(Requires a working viewer - batteries not included.)
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wordrec The word-level recognizer.
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textord The module that organizes(orders) text into lines and words.
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classify The low-level character classifiers.
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ccstruct Classes to hold information about a page as it is being processed.
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viewer The client side of a client server viewing system.
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Unfortunately, at this time, the server side is not available.
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image Image class and processing functions.
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dict Language model code.
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cutil Code for file I/O, lists, heaps etc, from the old C code.
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ccutil Somewhat newer code for lists, memory allocation etc from the
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old C++ code.
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About the Engine
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================
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This code is a raw OCR engine. It has NO PAGE LAYOUT ANALYSIS, NO OUTPUT
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FORMATTING, and NO UI. It can only process an image of a single column
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and create text from it. It can detect fixed pitch vs proportional text.
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Having said that, in 1995, this engine was in the top 3 in terms of character
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accuracy, and it compiles and runs on both Linux and Windows.
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As of 2.0, Tesseract is fully unicode (UTF-8) enabled, and can recognize 6
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languages "out of the box." Code and documentation is provided for the brave
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to train in other languages. See code.google.com/p/tesseract-ocr for more
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information on training.
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Using the Engine
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================
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Windows:
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The executable must reside in the same directory as the tessdata directory
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The command line is:
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tesseract <image.tif> <output> [-l langid]
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A windows executable (tesseract.exe) is included in the distribution, but
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may not work for you unless you also have the correct mfc and crt dlls.
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There is also a tessdll.dll, which you can use to run tesseract from your
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own program, but you may be better off building it yourself.
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Non-Windows:
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You have to tell Tesseract through a standard unix mechanism where to find
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its data directory. You must either:
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./configure
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make
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make install
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to move the data files to the standard place, or:
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export TESSDATA_PREFIX="directory in which your tessdata resides/"
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(or equivalent) in your .profile or whatever or setenv to set the environment
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variable. Note that the directory must end in a /
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HAVING tesseract and tessdata IN THE SAME DIRECTORY DOES NOT WORK ANY MORE.
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The command line is:
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tesseract <image.tif> <output> [-l langid]
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All Systems:
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The image file requires a .tif extension for its type to be recognized
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correctly. If a file exists with the .tif extension replaced by .uzn, then it
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will be interpreted as a UNLV-style zone file. (See www.isri.unlv.edu for
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details of the zone files.)
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langid may be one of the codes defined in ISO 639-3, and you must download
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the corresponding data files into your tessdata directory.
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