macOS - Create a "light and dark" wallpaper

ldwallpaper.inc

ldwallpaper() {
	if [ $# -lt 3 ] || [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
		echo "Creates a light and dark wallpaper for macOS."
		echo "Usage: ldwallpaper [-h] [--help] light_image dark_image out_heic"
		echo ""
		return 129
	fi
	command -v "exiv2" >/dev/null 2>&1 || { echo "exiv2 is not installed." >&2; return 1; }
	command -v "heif-enc" >/dev/null 2>&1 || { echo "libheif is not installed." >&2; return 1; }
	test -s "$1" || { echo "Light image does not exist." >&2; return 1; }
	test -s "$2" || { echo "Dark image does not exist." >&2; return 1; }
	test ! -e "$3" || { echo "Output image already exists." >&2; return 1; }
	f="$(basename "$1")"; n="${f%.*}"; e="${f##*.}"
	tmp="$(mktemp -d)"
	cp "$1" "$tmp/$f"
	cat << EOF > "$tmp/$n.xmp"
<?xpacket?>
<x:xmpmeta xmlns:x="adobe:ns:meta">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns">
<rdf:Description xmlns:apple_desktop="http://ns.apple.com/namespace/1.0"
apple_desktop:apr=
"YnBsaXN0MDDSAQMCBFFsEAFRZBAACA0TEQ/REMOVE/8BAQAAAAAAAAAFAAAAAAAAAAAAAAAAAAAAFQ=="/>
</rdf:RDF>
</x:xmpmeta>
EOF
	exiv2 -i X in "$tmp/$f"
	{ test "$e" = "png" && heif-enc -L "$tmp/$f" "$2" -o "$3"; } || heif-enc "$tmp/$f" "$2" -o "$3"
	rm -r "$tmp"
}

Allows you to convert a light and a dark wallpaper into one HEIC which can be set as desktop background in macOS, so that the proper version will be used depending on your system settings. If you use light mode, the light wallpaper will be shown. If you use dark mode, the dark wallpaper will be shown.

I built the function based on https://remove.codes/01-dynamic-wallpaper (credit where credit is due)

Interestingly, macOS doesn't indicate the file to be light/dark mode compatible, but it works anyways.

Example usage:

brew install exiv2 libheif
source ldwallpaper.inc
ldwallpaper light_wallpaper.jpg dark_wallpaper.jpg out_wallpaper.heic