it's a fast way to shade pictures
i was tired of shading every single page and you probably are too
first, make a layer where you quickcly put down random strokes where you think shadows would look nice. i personally like to do it in black
then, perform the auto action and
voilà! a convincing shading done in less than a minute!
the layer also has a different name to be recognizable.
just in case you want to go bak and fix stuff at full opacity, there's a reverse function too.