(keitai-l) japanese bitmap fonts - smallest possible?

apologies for seeming slightly off topic...

does anyone know how many pixels (X Y) are required to 
display readable japanese characters?
(for kana and kanji)
for example, for Roman letters one can easily display readable text
using 5x7 pixels per character.

it seems that 16x16 pixels per character would easily support any japanese text,
but can one go smaller?
what is typical?

this would come up if someone was making custom fonts for an i-appli, for example.

thanks!

-rolf