Imagemagickの高速化 mprとmpc ref: http://qiita.com/hadashiA/items/bf10881943a41fee238d

file0.txt

# hoge という字の画像を生成
$ convert -size 200x200 -background transparent -fill black -gravity Center label:hoge png:- | \
# それをbg.png と合成する
$ convert -composite - bg.png hoge.png

file1.txt

$ convert -size 200x200 -background transparent -fill black -gravity Center label:hoge -write mpr:hoge +delete mpr:hoge -composite bg.png hoge.png

file2.txt

$ convert bg.jpg bg.mpc

file3.txt

$ convert -size 200x200 -background transparent -fill black -gravity Center label:hoge -write mpr:hoge +delete mpr:hoge -composite bg.mpc hoge.png