for i in nav/original/*
do
echo $i
convert -background black -gravity center $i -resize 140x140 -extent 140x140 ${i/original/home}
convert -background black -gravity center $i -resize 80x80 -extent 100x100 ${i/original/sidebar}
convert -background white -negate -gravity center $i -resize 80x80 -extent 100x100 ${i/original/selected}
done