I see I can adjust my image between 8, 16, and 32 bits per channel, and when I create a new image I can choose between bitmap (1-bit) or 16-bit+ in all the other modes.
Is there a way to do a 4-bit mode? I'm trying to do some image editing for some e-ink displays (16-color grayscale, aka 4-bit) but I cannot for the life of me figure this out in Photoshop CS6, and most google results are just 'how to make an image greyscale'.
Alternatively, what software could I use to create and edit images in a 4-bit grayscale mode?