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0f9d507740
The last contribution from Google was in 2018
(see commit ce88adbf32).
Signed-off-by: Stefan Weil <sw@weilnetz.de>
90 lines
2.9 KiB
Plaintext
90 lines
2.9 KiB
Plaintext
UNICHARAMBIGS(5)
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================
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NAME
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----
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unicharambigs - Tesseract unicharset ambiguities
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DESCRIPTION
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-----------
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The unicharambigs file (a component of traineddata, see combine_tessdata(1) )
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is used by Tesseract to represent possible ambiguities between characters,
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or groups of characters.
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The file contains a number of lines, laid out as follow:
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...........................
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[num] <TAB> [char(s)] <TAB> [num] <TAB> [char(s)] <TAB> [num]
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...........................
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[horizontal]
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Field one:: the number of characters contained in field two
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Field two:: the character sequence to be replaced
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Field three:: the number of characters contained in field four
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Field four:: the character sequence used to replace field two
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Field five:: contains either 1 or 0. 1 denotes a mandatory
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replacement, 0 denotes an optional replacement.
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Characters appearing in fields two and four should appear in
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unicharset. The numbers in fields one and three refer to the
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number of unichars (not bytes).
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EXAMPLE
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-------
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...............................
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v1
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2 ' ' 1 " 1
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1 m 2 r n 0
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3 i i i 1 m 0
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...............................
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The first line is a version identifier.
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In this example, all instances of the '2' character sequence '''' will
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*always* be replaced by the '1' character sequence '"'; a '1' character
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sequence 'm' *may* be replaced by the '2' character sequence 'rn', and
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the '3' character sequence *may* be replaced by the '1' character
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sequence 'm'.
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Version 3.03 and on supports a new, simpler format for the unicharambigs
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file:
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...............................
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v2
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'' " 1
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m rn 0
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iii m 0
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...............................
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In this format, the "error" and "correction" are simple UTF-8 strings
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separated by a space, and, after another space, the same type specifier
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as v1 (0 for optional and 1 for mandatory substitution). Note the downside
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of this simpler format is that Tesseract has to encode the UTF-8 strings
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into the components of the unicharset. In complex scripts, this encoding
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may be ambiguous. In this case, the encoding is chosen such as to use the
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least UTF-8 characters for each component, ie the shortest unicharset
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components will make up the encoding.
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HISTORY
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-------
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The unicharambigs file first appeared in Tesseract 3.00; prior to that, a
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similar format, called DangAmbigs ('dangerous ambiguities') was used: the
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format was almost identical, except only mandatory replacements could be
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specified, and field 5 was absent.
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BUGS
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----
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This is a documentation "bug": it's not currently clear what should be done
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in the case of ligatures (such as 'fi') which may also appear as regular
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letters in the unicharset.
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SEE ALSO
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--------
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tesseract(1), unicharset(5)
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https://tesseract-ocr.github.io/tessdoc/Training-Tesseract-3.03%E2%80%933.05.html#the-unicharambigs-file
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AUTHOR
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------
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The Tesseract OCR engine was written by Ray Smith and his research groups
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at Hewlett Packard (1985-1995) and Google (2006-2018).
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