TESSERACT(1) TESSERACT(1)
NAME
tesseract - command-line OCR engine
SYNOPSIS
tesseract FILE OUTPUTBASE [OPTIONS]... [CONFIGFILE]...
DESCRIPTION
tesseract(1) is a commercial quality OCR engine originally developed at
HP between 1985 and 1995. In 1995, this engine was among the top 3
evaluated by UNLV. It was open-sourced by HP and UNLV in 2005, and has
been developed at Google since then.
IN/OUT ARGUMENTS
FILE
The name of the input file. This can either be an image file or a
text file.
Most image file formats (anything readable by Leptonica) are
supported.
A text file lists the names of all input images (one image name per
line). The results will be combined in a single file for each
output file format (txt, pdf, hocr, xml).
If FILE is stdin or - then the standard input is used.
OUTPUTBASE
The basename of the output file (to which the appropriate extension
will be appended). By default the output will be a text file with
.txt added to the basename unless there are one or more parameters
set which explicitly specify the desired output.
If OUTPUTBASE is stdout or - then the standard output is used.
OPTIONS
-c CONFIGVAR=VALUE
Set value for parameter CONFIGVAR to VALUE. Multiple -c arguments
are allowed.
--dpi N
Specify the resolution N in DPI for the input image(s). A typical
value for N is 300. Without this option, the resolution is read
from the metadata included in the image. If an image does not
include that information, Tesseract tries to guess it.
-l LANG, -l SCRIPT
The language or script to use. If none is specified, eng (English)
is assumed. Multiple languages may be specified, separated by plus
characters. Tesseract uses 3-character ISO 639-2 language codes
(see LANGUAGES AND SCRIPTS).
--psm N
Set Tesseract to only run a subset of layout analysis and assume a
certain form of image. The options for N are:
0 = Orientation and script detection (OSD) only.
1 = Automatic page segmentation with OSD.
2 = Automatic page segmentation, but no OSD, or OCR. (not implemented)
3 = Fully automatic page segmentation, but no OSD. (Default)
4 = Assume a single column of text of variable sizes.
5 = Assume a single uniform block of vertically aligned text.
6 = Assume a single uniform block of text.
7 = Treat the image as a single text line.
8 = Treat the image as a single word.
9 = Treat the image as a single word in a circle.
10 = Treat the image as a single character.
11 = Sparse text. Find as much text as possible in no particular order.
12 = Sparse text with OSD.
13 = Raw line. Treat the image as a single text line,
bypassing hacks that are Tesseract-specific.
--oem N
Specify OCR Engine mode. The options for N are:
0 = Original Tesseract only.
1 = Neural nets LSTM only.
2 = Tesseract + LSTM.
3 = Default, based on what is available.
--tessdata-dir PATH
Specify the location of tessdata path.
--user-patterns FILE
Specify the location of user patterns file.
--user-words FILE
Specify the location of user words file.
CONFIGFILE
The name of a config to use. The name can be a file in
tessdata/configs or tessdata/tessconfigs, or an absolute or
relative file path. A config is a plain text file which contains a
list of parameters and their values, one per line, with a space
separating parameter from value.
Interesting config files include:
• alto — Output in ALTO format (OUTPUTBASE.xml).
• hocr — Output in hOCR format (OUTPUTBASE.hocr).
• pdf — Output PDF (OUTPUTBASE.pdf).
• tsv — Output TSV (OUTPUTBASE.tsv).
• txt — Output plain text (OUTPUTBASE.txt).
• get.images — Write processed input images to file
(OUTPUTBASE.processedPAGENUMBER.tif).
• logfile — Redirect debug messages to file (tesseract.log).
• lstm.train — Output files used by LSTM training
(OUTPUTBASE.lstmf).
• makebox — Write box file (OUTPUTBASE.box).
• quiet — Redirect debug messages to /dev/null.
It is possible to select several config files, for example tesseract
image.png demo alto hocr pdf txt will create four output files
demo.alto, demo.hocr, demo.pdf and demo.txt with the OCR results.
Nota bene: The options -l LANG, -l SCRIPT and --psm N must occur before
any CONFIGFILE.
SINGLE OPTIONS
-h, --help
Show help message.
--help-extra
Show extra help for advanced users.
--help-psm
Show page segmentation modes.
--help-oem
Show OCR Engine modes.
-v, --version
Returns the current version of the tesseract(1) executable.
--list-langs
List available languages for tesseract engine. Can be used with
--tessdata-dir PATH.
--print-parameters
Print tesseract parameters.
LANGUAGES AND SCRIPTS
To recognize some text with Tesseract, it is normally necessary to
specify the language(s) or script(s) of the text (unless it is English
text which is supported by default) using -l LANG or -l SCRIPT.
Selecting a language automatically also selects the language specific
character set and dictionary (word list).
Selecting a script typically selects all characters of that script
which can be from different languages. The dictionary which is included
also contains a mix from different languages. In most cases, a script
also supports English. So it is possible to recognize a language that
has not been specifically trained for by using traineddata for the
script it is written in.
More than one language or script may be specified by using +. Example:
tesseract myimage.png myimage -l eng+deu+fra.
https://github.com/tesseract-ocr/tessdata_fast provides fast language
and script models which are also part of Linux distributions.
For Tesseract 4, tessdata_fast includes traineddata files for the
following languages:
afr (Afrikaans), amh (Amharic), ara (Arabic), asm (Assamese), aze
(Azerbaijani), aze_cyrl (Azerbaijani - Cyrilic), bel (Belarusian), ben
(Bengali), bod (Tibetan), bos (Bosnian), bre (Breton), bul (Bulgarian),
cat (Catalan; Valencian), ceb (Cebuano), ces (Czech), chi_sim (Chinese
simplified), chi_tra (Chinese traditional), chr (Cherokee), cos
(Corsican), cym (Welsh), dan (Danish), deu (German), div (Dhivehi), dzo
(Dzongkha), ell (Greek, Modern, 1453-), eng (English), enm (English,
Middle, 1100-1500), epo (Esperanto), equ (Math / equation detection
module), est (Estonian), eus (Basque), fas (Persian), fao (Faroese),
fil (Filipino), fin (Finnish), fra (French), frk (Frankish), frm
(French, Middle, ca.1400-1600), fry (West Frisian), gla (Scottish
Gaelic), gle (Irish), glg (Galician), grc (Greek, Ancient, to 1453),
guj (Gujarati), hat (Haitian; Haitian Creole), heb (Hebrew), hin
(Hindi), hrv (Croatian), hun (Hungarian), hye (Armenian), iku
(Inuktitut), ind (Indonesian), isl (Icelandic), ita (Italian), ita_old
(Italian - Old), jav (Javanese), jpn (Japanese), kan (Kannada), kat
(Georgian), kat_old (Georgian - Old), kaz (Kazakh), khm (Central
Khmer), kir (Kirghiz; Kyrgyz), kmr (Kurdish Kurmanji), kor (Korean),
kor_vert (Korean vertical), lao (Lao), lat (Latin), lav (Latvian), lit
(Lithuanian), ltz (Luxembourgish), mal (Malayalam), mar (Marathi), mkd
(Macedonian), mlt (Maltese), mon (Mongolian), mri (Maori), msa (Malay),
mya (Burmese), nep (Nepali), nld (Dutch; Flemish), nor (Norwegian), oci
(Occitan post 1500), ori (Oriya), osd (Orientation and script detection
module), pan (Panjabi; Punjabi), pol (Polish), por (Portuguese), pus
(Pushto; Pashto), que (Quechua), ron (Romanian; Moldavian; Moldovan),
rus (Russian), san (Sanskrit), sin (Sinhala; Sinhalese), slk (Slovak),
slv (Slovenian), snd (Sindhi), spa (Spanish; Castilian), spa_old
(Spanish; Castilian - Old), sqi (Albanian), srp (Serbian), srp_latn
(Serbian - Latin), sun (Sundanese), swa (Swahili), swe (Swedish), syr
(Syriac), tam (Tamil), tat (Tatar), tel (Telugu), tgk (Tajik), tha
(Thai), tir (Tigrinya), ton (Tonga), tur (Turkish), uig (Uighur;
Uyghur), ukr (Ukrainian), urd (Urdu), uzb (Uzbek), uzb_cyrl (Uzbek -
Cyrilic), vie (Vietnamese), yid (Yiddish), yor (Yoruba)
To use a non-standard language pack named foo.traineddata, set the
TESSDATA_PREFIX environment variable so the file can be found at
TESSDATA_PREFIX/tessdata/foo.traineddata and give Tesseract the
argument -l foo.
For Tesseract 4, tessdata_fast includes traineddata files for the
following scripts:
Arabic, Armenian, Bengali, Canadian_Aboriginal, Cherokee, Cyrillic,
Devanagari, Ethiopic, Fraktur, Georgian, Greek, Gujarati, Gurmukhi,
HanS (Han simplified), HanS_vert (Han simplified, vertical), HanT (Han
traditional), HanT_vert (Han traditional, vertical), Hangul,
Hangul_vert (Hangul vertical), Hebrew, Japanese, Japanese_vert
(Japanese vertical), Kannada, Khmer, Lao, Latin, Malayalam, Myanmar,
Oriya (Odia), Sinhala, Syriac, Tamil, Telugu, Thaana, Thai, Tibetan,
Vietnamese.
The same languages and scripts are available from
https://github.com/tesseract-ocr/tessdata_best. tessdata_best provides
slow language and script models. These models are needed for training.
They also can give better OCR results, but the recognition takes much
more time.
Both tessdata_fast and tessdata_best only support the LSTM OCR engine.
There is a third repository, https://github.com/tesseract-ocr/tessdata,
with models which support both the Tesseract 3 legacy OCR engine and
the Tesseract 4 LSTM OCR engine.
CONFIG FILES AND AUGMENTING WITH USER DATA
Tesseract config files consist of lines with parameter-value pairs
(space separated). The parameters are documented as flags in the source
code like the following one in tesseractclass.h:
STRING_VAR_H(tessedit_char_blacklist, "", "Blacklist of chars not to
recognize");
These parameters may enable or disable various features of the engine,
and may cause it to load (or not load) various data. For instance,
let’s suppose you want to OCR in English, but suppress the normal
dictionary and load an alternative word list and an alternative list of
patterns — these two files are the most commonly used extra data files.
If your language pack is in /path/to/eng.traineddata and the hocr
config is in /path/to/configs/hocr then create three new files:
/path/to/eng.user-words:
the
quick
brown
fox
jumped
/path/to/eng.user-patterns:
1-\d\d\d-GOOG-411
www.\n\\\*.com
/path/to/configs/bazaar:
load_system_dawg F
load_freq_dawg F
user_words_suffix user-words
user_patterns_suffix user-patterns
Now, if you pass the word bazaar as a CONFIGFILE to Tesseract,
Tesseract will not bother loading the system dictionary nor the
dictionary of frequent words and will load and use the eng.user-words
and eng.user-patterns files you provided. The former is a simple word
list, one per line. The format of the latter is documented in
dict/trie.h on read_pattern_list().
ENVIRONMENT VARIABLES
TESSDATA_PREFIX
If the TESSDATA_PREFIX is set to a path, then that path is used to
find the tessdata directory with language and script recognition
models and config files. Using --tessdata-dir PATH is the
recommended alternative.
OMP_THREAD_LIMIT
If the tesseract executable was built with multithreading support,
it will normally use four CPU cores for the OCR process. While this
can be faster for a single image, it gives bad performance if the
host computer provides less than four CPU cores or if OCR is made
for many images. Only a single CPU core is used with
OMP_THREAD_LIMIT=1.
HISTORY
The engine was developed at Hewlett Packard Laboratories Bristol and at
Hewlett Packard Co, Greeley Colorado between 1985 and 1994, with some
more changes made in 1996 to port to Windows, and some C++izing in
1998. A lot of the code was written in C, and then some more was
written in C++. The C++ code makes heavy use of a list system using
macros. This predates STL, was portable before STL, and is more
efficient than STL lists, but has the big negative that if you do get a
segmentation violation, it is hard to debug.
Version 2.00 brought Unicode (UTF-8) support, six languages, and the
ability to train Tesseract.
Tesseract was included in UNLV’s Fourth Annual Test of OCR Accuracy.
See https://github.com/tesseract-ocr/docs/blob/main/AT-1995.pdf. Since
Tesseract 2.00, scripts are now included to allow anyone to reproduce
some of these tests. See
https://tesseract-ocr.github.io/tessdoc/TestingTesseract.html for more
details.
Tesseract 3.00 added a number of new languages, including Chinese,
Japanese, and Korean. It also introduced a new, single-file based
system of managing language data.
Tesseract 3.02 added BiDirectional text support, the ability to
recognize multiple languages in a single image, and improved layout
analysis.
Tesseract 4 adds a new neural net (LSTM) based OCR engine which is
focused on line recognition, but also still supports the legacy
Tesseract OCR engine of Tesseract 3 which works by recognizing
character patterns. Compatibility with Tesseract 3 is enabled by --oem
0. This also needs traineddata files which support the legacy engine,
for example those from the tessdata repository
(https://github.com/tesseract-ocr/tessdata).
For further details, see the release notes in the Tesseract
documentation
(https://tesseract-ocr.github.io/tessdoc/ReleaseNotes.html).
RESOURCES
Main web site: https://github.com/tesseract-ocr User forum:
https://groups.google.com/g/tesseract-ocr Documentation:
https://tesseract-ocr.github.io/ Information on training:
https://tesseract-ocr.github.io/tessdoc/Training-Tesseract.html
SEE ALSO
ambiguous_words(1), cntraining(1), combine_tessdata(1),
dawg2wordlist(1), shape_training(1), mftraining(1), unicharambigs(5),
unicharset(5), unicharset_extractor(1), wordlist2dawg(1)
AUTHOR
Tesseract development was led at Hewlett-Packard and Google by Ray
Smith. The development team has included:
Ahmad Abdulkader, Chris Newton, Dan Johnson, Dar-Shyang Lee, David
Eger, Eric Wiseblatt, Faisal Shafait, Hiroshi Takenaka, Joe Liu, Joern
Wanke, Mark Seaman, Mickey Namiki, Nicholas Beato, Oded Fuhrmann, Phil
Cheatle, Pingping Xiu, Pong Eksombatchai (Chantat), Ranjith
Unnikrishnan, Raquel Romano, Ray Smith, Rika Antonova, Robert Moss,
Samuel Charron, Sheelagh Lloyd, Shobhit Saxena, and Thomas Kielbus.
For a list of contributors see
https://github.com/tesseract-ocr/tesseract/blob/main/AUTHORS.
COPYING
Licensed under the Apache License, Version 2.0
01/11/2023 TESSERACT(1)
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