embed-image-in-transparent-background.sh

#!/bin/bash

# this script expects an image, a target resolution and an output file.
# it then outputs a new png image with the given resolution
# and the given image, centered with transparent background.
# requires imagemagick


image="$1"
targetres="$2"
outfile="$3"

tempdir="$(mktemp -d)/"

if [ -z "${image}" ] || [ -z "${targetres}" ] || [ -z "${outfile}" ] ; then
    echo "Usage: "./$(basename "$0")" /path/to/image.ext WidthxHeigth /path/to/output.png"
    echo "Please make sure to correctly specify height and width delimited by an x, otherwise unexpected sideeffects may happen!"
    exit
fi

if [ -f "${outfile}" ] ; then
    echo "[!] target file ${outfile} already exists!"
    exit
fi

targetwidth="$(echo "${targetres}" | cut -d "x" -f 1 | tr -d " ")"

convert -size "${targetres}" xc:none "${tempdir}/transparent.png"
convert -resize "${targetwidth}x" "${image}" "${tempdir}/image-resized.png"
composite -gravity center "${tempdir}/image-resized.png" "${tempdir}/transparent.png" "${outfile}"

rm -r "${tempdir}"
echo "[+] All done!"