You can do this with Particle Playground.
It’s a pain. I know. But after you messed around with the settings – you can take a weeks vacation!
(it’s a slow render)
Basically – a grid that shows characters.
Set the size and characters to be derived from the various colors of your original footage.
though it’s not choosing characters depending on what color/blackness the image is – it fakes it by scaling the characters instead.
Good luck,
Tobias