Node PDF

Node PDF is a set of tools that takes in PDF files and converts them to usable formats for data processing. The library supports both extracting text from searchable pdf files as well as performing OCR on pdfs which are just scanned images of text

Installation

To begin install the module.

npm install pdf-extract

After the library is installed you will need the following binaries accessible on your path to process pdfs.

• pdftk
  • pdftk splits multi-page pdf into single pages.
• pdftotext
  • pdftotext is used to extract text out of searchable pdf documents
• ghostscript
  • ghostscript is an ocr preprocessor which convert pdfs to tif files for input into tesseract
• tesseract
  • tesseract performs the actual ocr on your scanned images

OSX

To begin on OSX, first make sure you have the homebrew package manager installed.

pdftk is not available in Homebrew. However a gui install is available here. http://www.pdflabs.com/docs/install-pdftk/

pdftotext is included as part of the poppler utilities library. poppler can be installed via homebrew

brew install poppler

ghostscript can be install via homebrew

brew install gs

tesseract can be installed via homebrew as well

brew install tesseract

After tesseract is installed you need to install the alphanumeric config and an updated trained data file

cd <root of this module>
cp "./share/eng.traineddata" "/usr/local/Cellar/tesseract/3.02.02_3/share/tessdata/eng.traineddata"
cp "./share/dia.traineddata" "/usr/local/Cellar/tesseract/3.02.02_3/share/tessdata/dia.traineddata"
cp "./share/configs/alphanumeric" "/usr/local/Cellar/tesseract/3.02.02_3/share/tessdata/configs/alphanumeric"

Ubuntu

pdftk can be installed directly via apt-get

apt-get install pdftk

pdftotext is included in the poppler-utils library. To installer poppler-utils execute

apt-get install poppler-utils

ghostscript can be install via apt-get

apt-get install ghostscript

tesseract can be installed via apt-get. Note that unlike the osx install the package is called tesseract-ocr on Ubuntu, not tesseract

apt-get install tesseract-ocr

For the OCR to work, you need to have the tesseract-ocr binaries available on your path. If you only need to handle ASCII characters, the accuracy of the OCR process can be increased by limiting the tesseract output. To do this copy the alphanumeric file included with this pdf-extract module into the tess-data folder on your system. Also the eng.traineddata included with the standard tesseract-ocr package is out of date. This pdf-extract module provides an up-to-date version which you should copy into the appropriate location on your system

cd <root of this module>
cp "./share/eng.traineddata" "/usr/share/tesseract-ocr/tessdata/eng.traineddata"
cp "./share/configs/alphanumeric" "/usr/share/tesseract-ocr/tessdata/configs/alphanumeric"

SmartOS

pdftk can be installed directly via apt-get

apt-get install pdftk

pdftotext is included in the poppler-utils library. To installer poppler-utils execute

apt-get install poppler-utils

ghostscript can be install via pkgin. Note you may need to update the pkgin repo to include the additional sources provided by Joyent. Check http://www.perkin.org.uk/posts/9000-packages-for-smartos-and-illumos.html for details

pkgin install ghostscript

tesseract can be must be manually downloaded and compiled. You must also install leptonica before installing tesseract. At the time of this writing leptonica is available from http://www.leptonica.com/download.html, with the latest version tarball available from http://www.leptonica.com/source/leptonica-1.69.tar.gz

pkgin install autoconf
wget http://www.leptonica.com/source/leptonica-1.69.tar.gz
tar -xvzf leptonica-1.69.tar.gz
cd leptonica-1.69
./configure
make
[sudo] make install

After installing leptonic move on to tesseract. Tesseract is available from https://code.google.com/p/tesseract-ocr/downloads/list with the latest version available from https://code.google.com/p/tesseract-ocr/downloads/detail?name=tesseract-ocr-3.02.02.tar.gz&can=2&q=

wget https://code.google.com/p/tesseract-ocr/downloads/detail?name=tesseract-ocr-3.02.02.tar.gz&can=2&q=
tar -xvzf tesseract-ocr-3.02.02.tar.gz
cd tesseract-ocr
./configure
make
[sudo] make install

Windows

Important! You will have to add some variables to the PATH of your machine. You do this by right clicking your computer in file explorer, select Properties, select Advanced System Settings, Environment Variables. You can then add the folder that contains the executables to the path variable.

pdftk can be installed using the PDFtk Server installer found here: https://www.pdflabs.com/tools/pdftk-server/ It should autmatically add itself to the PATH, if not, the default install location is "C:\Program Files (x86)\PDFtk Server\bin"

pdftotext can be installed using the recompiled poppler utils for windows, which have been collected and bundled here: http://manifestwebdesign.com/2013/01/09/xpdf-and-poppler-utils-on-windows/ Unpack these in a folder, (example: "C:\poppler-utils") and add this to the PATH.

ghostscript for Windows can be found at: http://www.ghostscript.com/download/gsdnld.html Make sure you download the General Public License and the correct version (32/64bit). Install it and go to the installation folder (default: "C:\Program Files\gs\gs9.19") and go into the bin folder. Rename the gswin64c to gs, and add the bin folder to your PATH.

tesseract can be build, but you can also download an older version which seems to work fine. Downloads at: https://sourceforge.net/projects/tesseract-ocr-alt/files/ Version tested is tesseract-ocr-setup-3.02.02.exe, the default install location is "C:\Program Files (x86)\Tesseract-OCR" and is also added to the PATH. Note, this is only when you've checked that it will install for everyone on the machine.

Everything should work after all this! If not, try restarting to make sure the PATH variables are correctly used. This setup was tested on a Windows 10 Pro N 64bit machine.

Usage

OCR Extract from scanned image

Extract from a pdf file which contains a scanned image and no searchable text

const path = require("path")
const pdf_extract = require('pdf-extract')

console.log("Usage: node thisfile.js the/path/tothe.pdf")
const absolute_path_to_pdf = path.resolve(process.argv[2])
if (absolute_path_to_pdf.includes(" ")) throw new Error("will fail for paths w spaces like "+absolute_path_to_pdf)

const options = {
  type: 'ocr', // perform ocr to get the text within the scanned image
  ocr_flags: ['--psm 1'], // automatically detect page orientation
}
const processor = pdf_extract(absolute_path_to_pdf, options, ()=>console.log("Starting…"))
processor.on('complete', data => callback(null, data))
processor.on('error', callback)
function callback (error, data) { error ? console.error(error) : console.log(data.text_pages[0]) }

Text extract from searchable pdf

Extract from a pdf file which contains actual searchable text

const path = require("path")
const pdf_extract = require('./main.js')

console.log("Usage: node thisfile.js the/path/tothe.pdf")
const absolute_path_to_pdf = path.resolve(process.argv[2])
if (absolute_path_to_pdf.includes(" ")) throw new Error("will fail for paths w spaces like "+absolute_path_to_pdf)

const options = {
  type: 'text', // extract searchable text from PDF
  ocr_flags: ['--psm 1'], // automatically detect page orientation
  enc: 'UTF-8',  // optional, encoding to use for the text output
  mode: 'layout' // optional, mode to use when reading the pdf
}
const processor = pdf_extract(absolute_path_to_pdf, options, ()=>console.log("Starting…"))
processor.on('complete', data => callback(null, data))
processor.on('error', callback)
function callback (error, data) { error ? console.error(error) : console.log(data.text_pages[0]) }

Options

At a minimum you must specific the type of pdf extract you wish to perform

clean When the system performs extracts text from a multi-page pdf, it first splits the pdf into single pages. This are written to disk before the ocr occurs. For some applications these single page files can be useful. If you need to work with the single page pdf files after the ocr is complete, set the clean option to false as show below. Note that the single page pdf files are written to the system appropriate temp directory, so if you must copy the files to a more permanent location yourself after the ocr process completes

var options = {
  type: 'ocr' // (required), perform ocr to get the text within the scanned image
  enc: 'UTF-8' // optional, only applies to 'text' type
  mode: 'layout' // optional, only applies to 'text' type. Available modes are 'layout', 'simple', 'table' or 'lineprinter'. Default is 'layout'
  clean: false // keep the single page pdfs created during the ocr process
  ocr_flags: [
    '-psm 1',       // automatically detect page orientation
    '-l dia',       // use a custom language file
    'alphanumeric'  // only output ascii characters
  ]
}

Events

When processing, the module will emit various events as they occurr

page Emitted when a page has completed processing. The data passed with this event looks like

var data = {
  hash: <sha1 hash of the input pdf file here>
  text: <extracted text here>,
  index: 2,
  num_pages: 4,
  pdf_path: "~/Downloads/input_pdf_file.pdf",
  single_page_pdf_path: "/tmp/temp_pdf_file2.pdf"
}

error Emitted when an error occurs during processing. After this event is emitted processing will stop. The data passed with this event looks like

var data = {
  error: 'no file exists at the path you specified',
  pdf_path: "~/Downloads/input_pdf_file.pdf",
}

complete Emitted when all pages have completed processing and the pdf extraction is complete

var data = {
  hash: <sha1 hash of the input pdf file here>
  text_pages: <Array of Strings, one per page>,
  pdf_path: "~/Downloads/input_pdf_file.pdf",
  single_page_pdf_file_paths: [
    "/tmp/temp_pdf_file1.pdf",
    "/tmp/temp_pdf_file2.pdf",
    "/tmp/temp_pdf_file3.pdf",
    "/tmp/temp_pdf_file4.pdf",
  ]
}

log To avoid spamming process.stdout, log events are emitted instead.

Tests

To test that your system satisfies the needed dependencies and that module is functioning correctly execute the command in the pdf-extract module folder

cd <project_root>/node_modules/pdf-extract
npm test