DragonFly On-Line Manual Pages

UNICHARSET(5)                                                    UNICHARSET(5)

NAME
       unicharset - character properties file used by tesseract(1)

DESCRIPTION
       Tesseract's unicharset file contains information on each symbol
       (unichar) the Tesseract OCR engine is trained to recognize.

       A unicharset file (i.e. eng.unicharset) is distributed as part of a
       Tesseract language pack (i.e. eng.traineddata). For information on
       extracting the unicharset file, see combine_tessdata(1).

       The first line of a unicharset file contains the number of unichars in
       the file. After this line, each subsequent line provides information
       for a single unichar. The first such line contains a placeholder
       reserved for the space character. Each unichar is referred to within
       Tesseract by its Unichar ID, which is the line number (minus 1) within
       the unicharset file. Therefore, space gets unichar 0.

       Each unichar line in the unicharset file (v2+) may have four
       space-separated fields:

           'character' 'properties' 'script' 'id'

       Starting with Tesseract v3.02, more information may be given for each
       unichar:

           'character' 'properties' 'glyph_metrics' 'script' 'other_case' 'direction' 'mirror' 'normed_form'

       Entries:

       character
           The UTF-8 encoded string to be produced for this unichar.

       properties
           An integer mask of character properties, one per bit. From least to
           most significant bit, these are: isalpha, islower, isupper,
           isdigit, ispunctuation.

       glyph_metrics
           Ten comma-separated integers representing various standards for
           where this glyph is to be found within a baseline-normalized
           coordinate system where 128 is normalized to x-height.

           o   min_bottom, max_bottom: the ranges where the bottom of the
               character can be found.

           o   min_top, max_top: the ranges where the top of the character may
               be found.

           o   min_width, max_width: horizontal width of the character.

           o   min_bearing, max_bearing: how far from the usual start position
               does the leftmost part of the character begin.

           o   min_advance, max_advance: how far from the printer's cell left
               do we advance to begin the next character.

       script
           Name of the script (Latin, Common, Greek, Cyrillic, Han, null).

       other_case
           The Unichar ID of the other case version of this character (upper
           or lower).

       direction
           The Unicode BiDi direction of this character, as defined by ICU's
           enum UCharDirection. (0 = Left to Right, 1 = Right to Left, 2 =
           European Number...)

       mirror
           The Unichar ID of the BiDirectional mirror of this character. For
           example the mirror of open paren is close paren, but Latin Capital
           C has no mirror, so it remains a Latin Capital C.

       normed_form
           The UTF-8 representation of a "normalized form" of this unichar for
           the purpose of blaming a module for errors given ground truth text.
           For instance, a left or right single quote may normalize to an
           ASCII quote.

EXAMPLE (V2)
           ; 10 Common 46
           b 3 Latin 59
           W 5 Latin 40
           7 8 Common 66
           = 0 Common 93

       ";" is a punctuation character. Its properties are thus represented by
       the binary number 10000 (10 in hexadecimal).

       "b" is an alphabetic character and a lower case character. Its
       properties are thus represented by the binary number 00011 (3 in
       hexadecimal).

       "W" is an alphabetic character and an upper case character. Its
       properties are thus represented by the binary number 00101 (5 in
       hexadecimal).

       "7" is just a digit. Its properties are thus represented by the binary
       number 01000 (8 in hexadecimal).

       "=" is not punctuation nor a digit nor an alphabetic character. Its
       properties are thus represented by the binary number 00000 (0 in
       hexadecimal).

       Japanese or Chinese alphabetic character properties are represented by
       the binary number 00001 (1 in hexadecimal): they are alphabetic, but
       neither upper nor lower case.

EXAMPLE (V3.02)
           110
           NULL 0 NULL 0
           N 5 59,68,216,255,87,236,0,27,104,227 Latin 11 0 1 N
           Y 5 59,68,216,255,91,205,0,47,91,223 Latin 33 0 2 Y
           1 8 59,69,203,255,45,128,0,66,74,173 Common 3 2 3 1
           9 8 18,66,203,255,89,156,0,39,104,173 Common 4 2 4 9
           a 3 58,65,186,198,85,164,0,26,97,185 Latin 56 0 5 a
           . . .

CAVEATS
       Although the unicharset reader maintains the ability to read
       unicharsets of older formats and will assign default values to missing
       fields, the accuracy will be degraded.

       Further, most other data files are indexed by the unicharset file, so
       changing it without re-generating the others is likely to have dire
       consequences.

HISTORY
       The unicharset format first appeared with Tesseract 2.00, which was the
       first version to support languages other than English. The unicharset
       file contained only the first two fields, and the "ispunctuation"
       property was absent (punctuation was regarded as "0", as "=" is in the
       above example.

SEE ALSO
       tesseract(1), combine_tessdata(1), unicharset_extractor(1)

       http://code.google.com/p/tesseract-ocr/wiki/TrainingTesseract3

AUTHOR
       The Tesseract OCR engine was written by Ray Smith and his research
       groups at Hewlett Packard (1985-1995) and Google (2006-present).

                                  02/09/2012                     UNICHARSET(5)