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OCRODJVU(1) ocrodjvu manual OCRODJVU(1)

NAME

ocrodjvu - OCR for DjVu files

SYNOPSIS

ocrodjvu {-o | --save-bundled} output-djvu-file [option...] djvu-file

ocrodjvu {-i | --save-indirect} index-djvu-file [option...] djvu-file

ocrodjvu --save-script script-file [option...] djvu-file

ocrodjvu --in-place [option...] djvu-file

ocrodjvu --dry-run [option...] djvu-file

ocrodjvu {--version | --help | -h | --list-engines | --list-languages}

DESCRIPTION

ocrodjvu is a wrapper for OCR systems that allows you to perform OCR on DjVu files.

The following OCR engines are supported:

•OCRopus[1] (internally, ocrodjvu calls ocroscript's recognize (or rec-tess) command, so that ultimately Tesseract acts as the OCR backend);

•Cuneiform for Linux[2].

•Ocrad[3].

•GOCR[4].

•Stand-alone Tesseract[5].

OPTIONS

OCR engine options

-e, --engine=engine-id

Use this OCR engine.

The default is “tesseract”. (The default was “ocropus” prior to ocrodjvu 0.8.)

--list-engines

Print list of available OCR engines.

Options controlling output

-o, --save-bundled=output-djvu-file

Save OCR results as a bundled multi-page document into output-djvu-file.

-i, --save-indirect=index-djvu-file

Save OCR results as an indirect multi-page document. Use index-djvu-file as the index file name; put the component files into the same directory. The directory must exist and be writable.

--save-script=script-file

Save a djvused script with OCR results into script-file.

--in-place

Save OCR results in place.

--dry-run

Don't change any files, throw OCR results away.

It is mandatory to use exactly one of the above options.

--ocr-only

If OCR results are to be saved to a separate document (-o/--save-bundled or -i/--save-indirect), save only the pages selected for OCR.

The default is to save all pages, even when the -p/--pages option is in effect.

--clear-text

Remove existing hidden text if present in the pages not selected for OCR.

--save-raw-ocr=output-directory

Save raw OCR results (typically in the hOCR format) into output-directory. The directory must exist and be writable.

--raw-ocr-filename-template=template

Specifies the file naming scheme for raw OCR results.

The template language uses the Python string formatting syntax[6]. The following fields are available:

page, page+N, page-N

page number, optionally shifted by a number N

id

page identifier

id-ext

page identifier without file extension

The default template is “{id-ext}”.

Text segmentation options

-t lines, --details lines

Record location of every line. Don't record locations of particular words or characters.

This is the default for OCRopus 0.2. The option is ineffective with stand-alone Tesseract 2.0.

-t words, --details=words

Record location of every line and every word. Don't record locations of particular characters.

This is the default for most OCR engines.

This option is ineffective with OCRopus 0.2 and stand-alone Tesseract 2.0.

-t chars, --details=chars

Record location of every line, every word and every character.

This option is ineffective with OCRopus 0.2 and stand-alone Tesseract 2.0.

--word-segmentation=simple

Consider each non-empty sequence of non-whitespace characters a single word.

This is the default, despite being linguistically incorrect.

--word-segmentation=uax29

Use the Unicode Text Segmentation[7] algorithm to break lines into words.

This option breaks assumptions of some DjVu tools that words are separated by spaces, and therefore it is not recommended.

Other options

-l, --language=language-id

Set recognition language. language-id is typically an ISO 639-2/T three-letter code.

Tesseract ≥ 3.02 allows specifying multiple languages separated by “+” characters.

The default is always “eng” (English).

--list-languages

Print list of available languages for the currently selected OCR engine.

--render=mask

Render only masks of page images.

This is the default.

--render=foreground

Render only foreground layers of page images.

--render=all

Render all layers of page images.

This option is necessary to OCR DjVu files with invalid foreground/background separation.

-p, --pages=page-range

Specifies pages to process. page-range is a comma-separated list of sub-ranges. Each sub-range is either a single page (e.g. 17) or a contiguous range of pages (e.g. 37-42). Pages are numbered from 1.

The default is to process all pages.

-j, --jobs=n

Start up to n OCR threads.

The default is 1.

--version

Output version information and exit.

-h, --help

Display help and exit.

Advanced options

-D, --debug

To ease debugging, don't delete intermediate files.

-X key=value

This option allows controlling some details of how ocrodjvu operates.

--on-error=abort

Stop program execution when an exceptional situation (e.g., malformed output from the OCR engine, internal ocrodjvu error, etc.) occurs.

This is the default.

--on-error=resume

Attempt to recover from exceptional situations.

This option is strongly discouraged.

--html5

Use a HTML5 parser[8], which is more robust but slower than the default parser.

EXIT STATUS

One of the following exit values can be returned by ocrodjvu:

0

The program finished successfully.

1

A fatal error occurred.

2

The program recovered from an error (--on-error=resume).

ENVIRONMENT

The following environment variables affects ocrodjvu:

TMPDIR

ocrodjvu makes heavy use of temporary files. It will store them in a directory specified by this variable. The default is /tmp.

BUGS

Known bugs

Tesseract 3.00 is affected by a bug [9] making it produce invalid hOCR output in certain circumstances. ocrodjvu does not try recover from this fault (which couldn't be done reliably anyway) unless you pass the -X fix-html=1 option.

Extracting bounding boxes of particular characters (which happens when either --details=chars or --word-segmentation=uax29 is enabled) is slow with Tesseract < 3.04.

Reporting new bugs

Please report bugs at: https://github.com/jwilk/ocrodjvu/issues

SEE ALSO

djvu(1), djvu2hocr(1), hocr2djvused(1),

ocroscript(1), tesseract(1), cuneiform(1), ocrad(1), gocr(1)

NOTES

1.
OCRopus
https://code.google.com/p/ocropus/
2.
Cuneiform for Linux
https://launchpad.net/cuneiform-linux
3.
Ocrad
https://www.gnu.org/software/ocrad/
4.
GOCR
http://www-e.uni-magdeburg.de/jschulen/ocr/
5.
Tesseract
https://github.com/tesseract-ocr/tesseract
6.
Python string formatting syntax
https://docs.python.org/2/library/string.html#format-string-syntax
7.
Unicode Text Segmentation
https://unicode.org/reports/tr29/
8.
HTML5 parser
https://html.spec.whatwg.org/multipage/syntax.html#parsing
9.
https://groups.google.com/d/topic/tesseract-issues/AdZhdGFkTrA

2019-02-11 ocrodjvu 0.11