问题
How can I use sips, imagemagic, or another tool to convert an image to black and white (grayscale) via the command line?
回答1:
If you have imagemagick installed,
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)
If you don't care about losing the original file: mogrify -colorspace Gray file.
回答2:
use one of: -monochrome or -colorspace gray options for imagemagick (convert).
来源：https://stackoverflow.com/questions/7708368/how-can-i-convert-an-image-to-grayscale-via-the-command-line