Separates pages from a scanned book (in PDF format), straightens the pages, and OCRs the whole thing.

process-scanned-pdf.sh

#!/bin/bash

if [ $# -eq 0 ] ; then
	echo "Usage: $0 <input PDF> [output filename] [custom temp dir]"
	echo "\tSlices, Straightens, and OCRs scanned PDFs from books"
	echo ""
	echo "\tIf [output filename] is not provided, then outputs to <input>.normalized.pdf
	echo "\tIf [custom temp dir] is not provided, then uses a directory from 'mktemp' which is automatically deleted"
	echo
	echo "\tUses commands from packages poppler-utils, imagemagick, img2pdf, ghostscript, ocrmypdf"
	echo "\tAnd deskew, which must be retrieved from github ( https://github.com/galfar/deskew )"

	exit 2
fi

ifile="$1"
ofile="${2:-$(basename "$ifile" .pdf).normalized.pdf}"
tmp="${3:-$(mktemp -d -p '' 'process-scanned-pdf.XXXXXX')}"
rotate_degrees=270

mkdir -p "$tmp"
mkdir -p "$tmp/raw"

raw="source"

# uses commands
# pdfimages (poppler-utils)
# convert (imagemagick)
# deskew (find on github)
# img2pdf (img2pdf)
# gs (ghostscript)
# ocrmypdf (ocrmypdf)

# Extract PDF's pages into individual images
pdfimages -png "$ifile" "$tmp/raw/$raw"

# Seperate joint pages, and straighten them if they are crooked
find "$tmp/raw/" -name "$raw-*.png" -type f -print0 | while read -r -d $'\0' file ; do
	echo "$file"
	
	imgnbr="$(( 10#${file//[!0-9]/} ))"
	
	convert "$file" -rotate "$rotate_degrees" -crop '2x1@' "$tmp/raw_page-tmp-%d.png"
	
	deskew -b FFFFFF -o "$tmp/raw_page-$(( imgnbr * 2 + 0 )).png" "$tmp/raw_page-tmp-0.png"
	deskew -b FFFFFF -o "$tmp/raw_page-$(( imgnbr * 2 + 1 )).png" "$tmp/raw_page-tmp-1.png"
	
	img2pdf --pagesize A4 --output "$tmp/clean_page-$(( imgnbr * 2 + 0 )).pdf" "$tmp/raw_page-$(( imgnbr * 2 + 0 )).png"
	img2pdf --pagesize A4 --output "$tmp/clean_page-$(( imgnbr * 2 + 1 )).pdf" "$tmp/raw_page-$(( imgnbr * 2 + 1 )).png"
done
rm "$tmp/raw_page-tmp-0.png" "$tmp/raw_page-tmp-1.png"

# Combine them back into one PDF
find "$tmp/" -name "clean_page-*.pdf" -type f -print0 | \
	sort --zero-terminated --numeric-sort -t '-' --key=2 | \
	xargs -d '\0'  \
		gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile="$tmp/cleaned.pdf"

# OCR PDF
ocrmypdf "$tmp/cleaned.pdf" "$tmp/ocrd.pdf"

mv "$tmp/ocrd.pdf" "$ofile"

# if not $3 (eg: custom temp directory) then...
if [ -z "$3" ] ; then
	rm -r "$tmp"
fi