Copas : Meubah Gambar Berwarna Menjadi Hitam Putih

Langsung copas aja:

convert source.jpg -colorspace Gray destination.jpg (true grayscale only)
convert source.jpg -monochrome destination.jpg (true black and white)
convert source.jpg -separate destination.jpg (separate into gray channels)

sumber : http://stackoverflow.com/questions/7708368/how-can-i-convert-an-image-to-grayscale-via-the-command-line