Create pixelated versions of any number of album covers

make-12x12.sh

#!/bin/bash
# GUID:370EBDBF-00CF-4D6D-9772-4A2B941A016F

PIXELS="12"
TARGET_WIDTH="900"
BORDER_WIDTH="50"
TEMP="temp"
OUTPUT_FILE="12x12.png"
IMAGES=()

while [ -n "${1}" ]; do
	case "${1}" in
		--pixels|-p)
			PIXELS="${2}"
			shift
			;;
		--width|-w)
			TARGET_WIDTH="${2}"
			shift
			;;
		--border|-b)
			BORDER_WIDTH="${2}"
			shift
			;;
		--output|-o)
			OUTPUT_FILES="${2}"
			shift
			;;
		-*)
			echo "$0 [--pixels <pixels>] [--width <width>] [--border <border>] <image1> <image2> <image3> <image4>"
			exit 1
			;;
		*)
			IMAGES=("${IMAGES[@]}" "${1}")
	esac
	shift
done

trap removeTemp SIGHUP SIGINT SIGTERM

mkdir -p "${TEMP}"

function removeTemp {
	rm -rf "${TEMP}"
	exit
}

# create alpha channel
ppmmake 0,0,0 100 100 | pnmtopng | convert - -fill white -draw 'circle 50,50, 97,50' - | pngtopnm | pnmtile $(($PIXELS*100)) $(($PIXELS*100)) | pamscale --width=${TARGET_WIDTH} --height="${TARGET_WIDTH}" > "${TEMP}/alphachannel.pnm"
ppmmake 0,0,0, "${TARGET_WIDTH}" "${TARGET_WIDTH}" > "${TEMP}/black.pnm"

# scale picture down
function createSmallPicture {
	anytopnm "${1}" 2> /dev/null | pamscale --width="${PIXELS}" --height="${PIXELS}" | pamscale --width="${TARGET_WIDTH}" --height="${TARGET_WIDTH}" > "${TEMP}/image.pnm"
	cat "${TEMP}/black.pnm" | pamcomp --alpha="${TEMP}/alphachannel.pnm" "${TEMP}/image.pnm" | pnmpad --black --left="${BORDER_WIDTH}" --right="${BORDER_WIDTH}" --top="${BORDER_WIDTH}" --bottom="${BORDER_WIDTH}"
}

number="${#IMAGES[*]}"
across="1"
down="${number}"

getFactors() {
	(
		echo "number=${1}"
		echo "s=sqrt(number)"
		echo "while (s > 0) {"
		echo "if (number % s == 0) {number/s; s; halt}"
		echo "s=s-1"
		echo "}"
	) | bc
}

read across down <<<$(getFactors $number)

for ((d=0; d<${down}; d++)); do
	for ((a=0; a<${across}; a++)); do
		createSmallPicture "${IMAGES[$(($d*$across+$a))]}" > "${TEMP}/tile-$d-$a.pnm"
	done
done

pamundice --across=${across} --down=${down} "${TEMP}/tile-%1d-%1a.pnm" | pnmtopng > "${OUTPUT_FILE}"

removeTemp