Split out image formatting

format_image.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+set -e
+
+magick "$1"'[0]' -resize 512x1662\> -dither FloydSteinberg -remap pattern:gray50 pbm:-

print_image.sh

@@ -2,7 +2,7 @@
 set -e
 dev=/dev/usb/lp0
 
-image="$(magick "$1"'[0]' -resize 512x1662\> -dither FloydSteinberg -remap pattern:gray50 pbm:- | base64)"
+image="$(./format_image "$1" | base64)"
 data_header="$(echo "$image" | base64 -d | sed -n '2p')"
 data="$(echo "$image" | base64 -d | tail -n +3 | base64)"