Imagemagick convert notes

Helping myself remember how to do common things using imagemagick’s (excellent but many-optioned) convert utility.

convert -scale 10% {in} {out}

# convert to black and white
convert -type Grayscale {in} {out}
convert -monochrome {in} {out}

# invert colours
convert -negate in out

convert -rotate {in} {out} 

# make the given colour (e.g. here white) transparent
convert -transparent white {in} {out}
# make transparent white
convert -fill white -opaque none {in} {out}

Make square (for thumbnailing)

convert -background transparent -gravity center -extent 145x145 file1 file2