On the top is a normal 2BPP tile. This represents the letter "A".
On the bottom is the same tile, de-compressed. An "A".
Example: Normal 2BPP has 4 colors. The decompressed tile has 2.
(imagine r=red, b=blue, g=green, x=black, w=white)

|x b b b b x b b|
|x b b r r r b b|
|x b g r r r g b|
|x b g r r r g g|
|x g g r x x g g|
|x g r x x x g r|
|x r r x x r r r|
|x r r r r r r r|

-----------------

|x x x x x x x x|
|x x x w w w x x|
|x x w w w w w x|
|x x w w w w w w|
|x w w w x x w w|
|x w w x x x w w|
|x w w x x w w w|
|x w w w w w w w|
|x w w w w x w w|
|x w w x x x w w|
|x w w x x x w w|
|x w w x x x w w|
|x w w x x x w w|
|x w x x x x w x|
|x x x x x x x x|
|x x x x x x x x|