Makefile for trimming PNG files and making them 2-bit black and white

Makefile

SRC=.
DST=2b
FILES=*.png

trim $(DST)/$(FILES): $(SRC)/$(FILES)
	for file in $(SRC)/$(FILES); do \
	    [ ! -f $(DST)/$$file -o $(SRC)/$$file -nt $(DST)/$$file ] \
	    && echo $$file \
	    && convert $(SRC)/$$file -dither none -colors 2 -trim +repage $(DST)/$$file; \
	done