How Can I Extract Bitplanes Of A Gray Image?

hi there. how can i extract bitplanes of a gray image in C#?
i wanna read a gray picture from some place and so :
a) show it with biplane1
b)show it with biplane1 and 2
c)show it with biplane1 and 2 and 3
d)show it with biplane1 and 2 and 3 and 4

i should enable the "redo" and "undo" actions

please help

(actually i dont know how can i reach the value of a pixel as an integer ? )

thanks