UNICHARAMBIGS(5) UNICHARAMBIGS(5)
NAME
unicharambigs - Tesseract unicharset ambiguities
DESCRIPTION
The unicharambigs file (a component of traineddata, see
combine_tessdata(1) ) is used by Tesseract to represent possible
ambiguities between characters, or groups of characters.
The file contains a number of lines, laid out as follow:
[num] <TAB> [char(s)] <TAB> [num] <TAB> [char(s)] <TAB> [num]
Field one the number of characters
contained in field two
Field two the character sequence to
be replaced
Field three the number of characters
contained in field four
Field four the character sequence
used to replace field two
Field five contains either 1 or 0. 1
denotes a mandatory
replacement, 0 denotes an
optional replacement.
Characters appearing in fields two and four should appear in
unicharset. The numbers in fields one and three refer to the number of
unichars (not bytes).
EXAMPLE
v1
2 ' ' 1 " 1
1 m 2 r n 0
3 i i i 1 m 0
The first line is a version identifier. In this example, all instances
of the 2 character sequence '' will always be replaced by the 1
character sequence "; a 1 character sequence m may be replaced by the 2
character sequence rn, and the 3 character sequence may be replaced by
the 1 character sequence m.
Version 3.03 and on supports a new, simpler format for the
unicharambigs file:
v2
'' " 1
m rn 0
iii m 0
In this format, the "error" and "correction" are simple UTF-8 strings
separated by a space, and, after another space, the same type specifier
as v1 (0 for optional and 1 for mandatory substitution). Note the
downside of this simpler format is that Tesseract has to encode the
UTF-8 strings into the components of the unicharset. In complex
scripts, this encoding may be ambiguous. In this case, the encoding is
chosen such as to use the least UTF-8 characters for each component, ie
the shortest unicharset components will make up the encoding.
HISTORY
The unicharambigs file first appeared in Tesseract 3.00; prior to that,
a similar format, called DangAmbigs (dangerous ambiguities) was used:
the format was almost identical, except only mandatory replacements
could be specified, and field 5 was absent.
BUGS
This is a documentation "bug": it’s not currently clear what should be
done in the case of ligatures (such as fi) which may also appear as
regular letters in the unicharset.
SEE ALSO
tesseract(1), unicharset(5)
https://tesseract-ocr.github.io/tessdoc/Training-Tesseract-3.03%E2%80%933.05.html#the-unicharambigs-file
AUTHOR
The Tesseract OCR engine was written by Ray Smith and his research
groups at Hewlett Packard (1985-1995) and Google (2006-present).
01/11/2023 UNICHARAMBIGS(5)
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