unsearchable2searchablepdfa.sh

A script that will create a PDF/A file with searchable & copyable text, from a source PDF file that (mostly, or totally) hasn’t.

Requires:

• convert imagemagick
• gs ghostscript
• optipng optipng
• tesseract tesseract-ocr or tesseract (+tesseract-ocr-fra, tesseract-ocr-spa, … or tesseract-data-fra, tesseract-data-spa, … )

The script creates page bitmaps from the original PDF file, applies OCR to them, and recombines the bitmaps and text into a searchable PDF/A file.

How to call it:

unsearchable2searchablepdfa.sh -l language -d targetDPI pdfFile

E.g.:

unsearchable2searchablepdfa.sh -l eng -d 300 scannedpages.pdf

You’ll most likely want to apply this to PDF files consisting of scanned pages bitmaps only.

#!/bin/bash

target_language=eng  # Remember to install required tesseract language package: eng;spa;fra;deu;...
dpi=300

while getopts ":d:l:" opt; do
  case $opt in
    d) dpi="$OPTARG"
    ;;
    l) target_language="$OPTARG"
    ;;
    \?) echo "Invalid option -$OPTARG" >&2
    echo "Usage:" >&2
    echo "$(basename $0) [-d dpi] [-l language] pdfFile"
    echo
    echo "Examples:"
    echo "$(basename $0)"
    echo "$(basename $0) -d $dpi -l $target_language scannedpages.pdf"
    exit 1
    ;;
  esac
done
shift $((OPTIND-1))

echo "Executing: $(basename $0) -d $dpi -l $target_language $1"

TMP_DIR=$(mktemp -d /tmp/tmpdir.XXXXXXXXXXXX)
SOURCE_FILE=$(readlink -f "$1")

echo
echo Converting $SOURCE_FILE to $dpi DPI bitmaps in $TMP_DIR ...
convert -density $dpi -background white -alpha remove "$SOURCE_FILE" "$TMP_DIR"/page-%04d.png


echo
echo Losslessly compressing bitmaps...
optipng -o2 "$TMP_DIR"/*.png 2> >(grep Processing >&2)

TARGET_DIR=$(dirname "$SOURCE_FILE")
BASE_NAME=$(basename -- "$SOURCE_FILE")
TARGET_NAME="${BASE_NAME%.*}"
TARGET_FILE="$TARGET_DIR/$TARGET_NAME-searchable.pdf"

echo
echo OCR: Converting bitmaps in $TMP_DIR to searchable PDF ...

find "$TMP_DIR"/ -iname '*.png' -type f -printf "$TMP_DIR/%f\n" | sort > "$TMP_DIR/files.txt"
tesseract -l $target_language --dpi $dpi --psm 1 "$TMP_DIR/files.txt" "$TMP_DIR/raw" pdf 2> >(grep Page >&2)

echo
echo Making searchable PDF validate against PDF/A ...
gs -o "$TARGET_FILE" -dPDFA=2 -dPDFACompatibilityPolicy=1 -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sColorConversionStrategy=UseDeviceIndependentColor "$TMP_DIR/raw.pdf" 2> >(grep Page >&2)

rm -rf "$TMP_DIR"

echo
echo Finished, see $TARGET_FILE

Image Credits:
Papirus icon for Terminal (modified) | GNU General Public License, version 3

Licensing:
This content is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
For your attributions to us please use the word »tuxwise«, and the link https://tuxwise.net.