bilayer2djvu

#!/bin/bash
set -ue # die on undefined variables / non-zero exit code

usage() {
	cat <<END
Usage: $0 [-options ...] <low-color files mask> <high-color files mask> <output file.djvu>
Options:
	-d dpi
		DPI passed to encoders
		[default 600]
	-q <colors>
		Quantizes low-color images to <colors> colors and encodes using cpaldjvu
	-t <threshold>
		Reduce low-color images to bilevel with specified threshold and encode with cjb2
		[default is to encode using cjb2 with 50% threshold]
	-r <factor>
		Resize high-color files to 1/<factor> by both dimensions before encoding, reducing
		their dpi accordingly (use -r "" to disable). <factor> must be integer in [1..12].
		[default 3]
	-c <color>
		Sets the color of the monochrome text. Accepts HTML color names and RRGGBB form.
		[default "black"]
	-h
		This help message
END
	exit $1
}

declare dpi=600 quantize= resize=3 threshold=50% mono=black

test_int() {
	if ! test "$1" -eq "$1"; then
		echo "$2 $1 should be integer, aborting"
		exit 1
	fi
	return 0
}

while getopts ":d:q:r:t:c:h" OPT; do
	case "$OPT" in
		d)
			dpi="$OPTARG"
			test_int "$dpi" "DPI"
			;;
		q)
			quantize="$OPTARG"
			test_int "$quantize" "Number of colors"
			echo 'Warning: discarding existing BG44 from cpaldjvu output' >&2
			;;
		t)
			threshold="$OPTARG"
			;;
		r)
			resize="$OPTARG"
			test_int "$resize" "Resize factor"
			if (( resize < 1 || resize > 12 )); then
				echo "Resize factor $resize should be in [1..12] range, aborting"
				exit 1
			fi
			;;
		c)
			mono="$OPTARG"
			;;
		h)
			usage 0
			;;
		*)
			echo "Invalid option: $OPT $OPTARG"
			usage 1
			;;
	esac
done
shift $(($OPTIND-1)) # cut the parameters
[ $# -eq 3 ] || usage 1;

if [ -e "$3" ]; then
	echo "$3 already exists, aborting"
	exit 1
fi

# this should unwrap the masks
declare -a lowcolor=($1) highcolor=($2)

if [ ${#lowcolor[@]} -ne ${#highcolor[@]} ]; then
	echo "Amounts of low-color and high color images do not match!"
	echo "Don't know what to do, aborting"
	exit 1
fi

declare -a tempfiles=()

for ((i=0; i<${#lowcolor[@]}; i++)); do # c-style for loop to use two arrays simultaneously
	# here comes the magic from http://djvu-soft.narod.ru/scan/back_glue.htm
	# first, the BG44 layer from the high-color image (to be used as FG44)
	declare hdpi=
	if [ "$resize" ]; then
		# got the correct formula from github.com/ashipunov/img2djvu. Thank you!
		newsize="$(identify -format "%[fx:ceil(w/$resize)]x%[fx:ceil(h/$resize)]!" "${highcolor[$i]}")"
		convert -verbose -resize "$newsize" "${highcolor[$i]}" "${highcolor[$i]}.ppm"
		hdpi="$((dpi/resize))"
	else
		convert -verbose "${highcolor[$i]}" "${highcolor[$i]}.ppm"
		hdpi="$dpi"
	fi
	c44 -dpi "$hdpi" "${highcolor[$i]}.ppm" "${highcolor[$i]}.c44"
	rm "${highcolor[$i]}.ppm"
	djvuextract "${highcolor[$i]}.c44" BG44="${highcolor[$i]}.c44raw"
	rm "${highcolor[$i]}.c44"
	# second, the low-color part
	if [ "$quantize" ]; then
		# dithering is compressed worse by cpaldjvu, looks badly with zooming and makes no sense in the context
		convert -verbose +dither -colors "$quantize" "${lowcolor[$i]}" "${lowcolor[$i]}.ppm"
		cpaldjvu -verbose -dpi "$dpi" -colors "$quantize" "${lowcolor[$i]}.ppm" "${lowcolor[$i]}.cpal"
		rm "${lowcolor[$i]}.ppm"
		# leave out the BG44 from cpal file; we'll replace it with the high-color part
		djvuextract "${lowcolor[$i]}.cpal" FGbz="${lowcolor[$i]}.fgbz" Sjbz="${lowcolor[$i]}.sjbz"
		rm "${lowcolor[$i]}.cpal"
		djvumake "${lowcolor[$i]}.djv" INFO=,,"$dpi" Sjbz="${lowcolor[$i]}.sjbz" BG44="${highcolor[$i]}.c44raw" FGbz="${lowcolor[$i]}.fgbz"
		rm "${lowcolor[$i]}.fgbz" "${lowcolor[$i]}.sjbz"
	else
		convert -verbose -threshold $threshold "${lowcolor[$i]}" "${lowcolor[$i]}.pbm"
		cjb2 -verbose -dpi "$dpi" "${lowcolor[$i]}.pbm" "${lowcolor[$i]}.cjb"
		rm "${lowcolor[$i]}.pbm"
		djvuextract "${lowcolor[$i]}.cjb" Sjbz="${lowcolor[$i]}.cjbraw"
		rm "${lowcolor[$i]}.cjb"
		djvumake "${lowcolor[$i]}.djv" INFO=,,"$dpi" Sjbz="${lowcolor[$i]}.cjbraw" BG44="${highcolor[$i]}.c44raw" "FGbz=#$mono"
		rm "${lowcolor[$i]}.cjbraw"
	fi
	rm "${highcolor[$i]}.c44raw" 
	tempfiles+=("${lowcolor[$i]}.djv")
done
djvm -c "$3" "${tempfiles[@]}"
rm "${tempfiles[@]}"