PIL: problem to convert an image array to PIL format

[Sverre]

After converting a PIL image in memory to an array with numpy.asarray
(), I make a adthreshold() with pymorph() with the result, that all
pixels in the array are either false or true (boolean). But my try to
convert this back into PIL format is failing

img = Image.fromarray(rawimg, '1')

because a true will be interpreted as integer 1 ), so that 7 pixels
are black and one white. Has someone a solution, so that a  picture
inly with "true" values doesn't look like this?

http://img707.imageshack.us/img707/6051/p012.jpg