annotate mupdf-source/thirdparty/tesseract/doc/unicharambigs.5.asc @ 46:7ee69f120f19 default tip

>>>>> tag v1.26.5+1 for changeset b74429b0f5c4
author Franz Glasner <fzglas.hg@dom66.de>
date Sat, 11 Oct 2025 17:17:30 +0200
parents b50eed0cc0ef
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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2
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1 UNICHARAMBIGS(5)
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2 ================
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3
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4 NAME
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5 ----
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6 unicharambigs - Tesseract unicharset ambiguities
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7
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8 DESCRIPTION
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9 -----------
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10 The unicharambigs file (a component of traineddata, see combine_tessdata(1) )
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11 is used by Tesseract to represent possible ambiguities between characters,
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12 or groups of characters.
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13
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14 The file contains a number of lines, laid out as follow:
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16 ...........................
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17 [num] <TAB> [char(s)] <TAB> [num] <TAB> [char(s)] <TAB> [num]
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18 ...........................
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20 [horizontal]
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21 Field one:: the number of characters contained in field two
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22 Field two:: the character sequence to be replaced
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23 Field three:: the number of characters contained in field four
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24 Field four:: the character sequence used to replace field two
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25 Field five:: contains either 1 or 0. 1 denotes a mandatory
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26 replacement, 0 denotes an optional replacement.
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28 Characters appearing in fields two and four should appear in
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29 unicharset. The numbers in fields one and three refer to the
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30 number of unichars (not bytes).
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32 EXAMPLE
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33 -------
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34
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35 ...............................
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36 v1
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37 2 ' ' 1 " 1
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38 1 m 2 r n 0
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39 3 i i i 1 m 0
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40 ...............................
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41
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42 The first line is a version identifier.
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43 In this example, all instances of the '2' character sequence '''' will
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44 *always* be replaced by the '1' character sequence '"'; a '1' character
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45 sequence 'm' *may* be replaced by the '2' character sequence 'rn', and
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46 the '3' character sequence *may* be replaced by the '1' character
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47 sequence 'm'.
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48
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49 Version 3.03 and on supports a new, simpler format for the unicharambigs
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50 file:
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51
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52 ...............................
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53 v2
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54 '' " 1
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55 m rn 0
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56 iii m 0
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57 ...............................
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58
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59 In this format, the "error" and "correction" are simple UTF-8 strings
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60 separated by a space, and, after another space, the same type specifier
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61 as v1 (0 for optional and 1 for mandatory substitution). Note the downside
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62 of this simpler format is that Tesseract has to encode the UTF-8 strings
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63 into the components of the unicharset. In complex scripts, this encoding
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64 may be ambiguous. In this case, the encoding is chosen such as to use the
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65 least UTF-8 characters for each component, ie the shortest unicharset
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66 components will make up the encoding.
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67
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68 HISTORY
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69 -------
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70 The unicharambigs file first appeared in Tesseract 3.00; prior to that, a
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71 similar format, called DangAmbigs ('dangerous ambiguities') was used: the
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72 format was almost identical, except only mandatory replacements could be
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73 specified, and field 5 was absent.
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74
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75 BUGS
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76 ----
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77 This is a documentation "bug": it's not currently clear what should be done
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78 in the case of ligatures (such as 'fi') which may also appear as regular
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79 letters in the unicharset.
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80
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81 SEE ALSO
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82 --------
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83 tesseract(1), unicharset(5)
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84 https://tesseract-ocr.github.io/tessdoc/Training-Tesseract-3.03%E2%80%933.05.html#the-unicharambigs-file
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85
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86 AUTHOR
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87 ------
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88 The Tesseract OCR engine was written by Ray Smith and his research groups
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89 at Hewlett Packard (1985-1995) and Google (2006-2018).