This is by far my most common task, and I'd say I've wasted about 1000 mouse clicks on it in my raster-based program.
Because it's so common for me to start off desaturating an image and then posterizing it, I'd like to write a shell script that does the same, that way I can process an entire directory automagically and simply get on with my work... There are only so many hours in the day. If I can make my computer do all the mouse clicks for me, go away and drink a few cups of coffee while it does so, then come back to it, that's infinitely better for me.
So how can I accomplish these two tasks using the CLI?