how convert black and white picture to transparent->black scale picture?

[MxHeppa]

how convert black and white picture to transparent->black scale picture? if i want do intensity brush i understand i need such conversion. at least when i want remove paper element. i mean i think make some btushes in paper and scan therm.

[firstdefence]

You could use the erase white paper filter: Filters > Colour > Erase White Paper

Obviously, draw on white paper lol!