Padding tilesets script

#!/bin/bash
rm _*.png
s=${1:-32}
ss=$((s+2))
for f in $(find . -name "*@2x.png" -maxdepth 1); do
    echo "Paddding $f..."
    wo=`convert $f -ping -format "%w" info:`
    h=`convert $f -ping -format "%h" info:`
    w=$((wo + (wo / s)*2))
    convert $f \
     -crop ${s}x0 +repage \
     -define distort:viewport=${ss}x${h}-1-0 \
     -filter point \
     -distort SRT 0 +repage +append \
     -crop 0x${s} +repage \
     -define distort:viewport=${w}x${ss}-0-1 \
     -distort SRT 0 +repage -append \
       _$(basename $f)
done
for f in $(find . -name "_*@2x.png" -maxdepth 1); do
    echo "Downsizing $f..."
    convert "$f" -filter Point -resize '50%' "$(dirname $f)/$(basename -s "@2x.png" $f).png"
done