OCR for pdf/tiff/png/jpg (wrapper for GraphicsMagick and Tesseract OCR)

ocr.sh

#!/bin/bash

##############################################################################
# OCR
#
# Usage:
#  ocr.sh file.{png,pdf,jpg} ...
#
# Requires:
#  * Tesseract
#  * ImageMagick / GraphicsMagick
#  * Poppler Utils (pdfimages)
#  * apt install -y graphicsmagick poppler-utils tesseract-ocr tesseract-ocr-eng
##############################################################################

cleanup() {
  if [ -n "$tmpdir" ] && [ -d "$tmpdir" ]; then
    rm -r "$tmpdir"
  fi
  tmpdir=""
}

trim() {
  cat "$@"
}

remove() {
  rm "$@"
}

image_adjust() {
  local i="$1"; shift
  local j="$1"; shift
  image_resize_adjust "$i" "$j"
}

image_resize_adjust() {
  if [ -z "$CONVERT" ]; then
    if gm -version >/dev/null 2>&1; then
      CONVERT="gm convert"
    else
      CONVERT="convert"
    fi
  fi

  local i="$1"; shift
  local j="$1"; shift
  if [ -n "$1" ]; then
    local sz="$1"; shift
    $CONVERT "$i" \
      -resize "$sz" \
      -white-threshold 75% \
      -colorspace gray \
      -depth 8 \
      -compress lzw \
      "$j"
  else
    $CONVERT "$i" \
      -white-threshold 75% \
      -colorspace gray \
      -depth 8 \
      -compress lzw \
      "$j"
  fi
}

ocr_tiff() {
  local i="$1"
  local out="$2"
  local j="${i%.*}"
  echo "==> $j.txt"
  tesseract "$i" "$j" nobatch
  trim "$j.txt" >> "$out"
  #remove "$j.txt"
}

ocr_png() {
  local i="$1"
  local out="$2"
  local j="${i%.*}"
  image_adjust "$i" "$j-000.tif"
  ocr_tiff "$j-000.tif" "$out"
  remove "$j-000.tif"
}

ocr_jpeg() {
  ocr_png "$@"
}

ocr_pdf() {
  local i="$1"
  local out="$2"
  pdfimages -j "$i" "$tmpdir/$i"
  local j
  for j in "$tmpdir/$i"*.p[bp]m; do
    local k="${j%.*}"
    #convert_args="-white-threshold 75% -auto-level -compress lzw"
    #convert_args="-resize 400% -white-threshold 75% -colorspace gray -depth 8 -compress lzw"
    #convert "$j" $convert_args "$k.tif" && rm "$j"
    #convert "$j" -fill white -draw 'rectangle 0,0 425,650' -draw 'rectangle 730,300 850,900' -draw 'rectangle 0,850 850,900' -resize 400% -white-threshold 75% -colorspace gray -depth 8 -compress lzw "$k.tif"
    image_resize_adjust "$j" "$k.tif" '400%'
    ocr_tiff "$k.tif" "$out"
    remove "$k.tif"
  done
}

tmpdir=$(mktemp -p "${TMPDIR:-/tmp}" -d ocr-XXXXXXXX) || exit 1
trap cleanup 0

for i in "$@"; do
  out="${i%.*}.txt"
  : > $out
  case "${i,,}" in
    *.pdf)
      ocr_pdf "$i" "$out"
      ;;
    *.png)
      ocr_png "$i" "$out"
      ;;
    *.jpg|*.jpeg)
      ocr_jpeg "$i" "$out"
      ;;
    *.tif|*.tiff)
      ocr_tiff "$i" "$out"
      ;;
  esac
done