Converting image to black and white and use it as array

I'm trying to convert a colored image to a black and white one.

The original image is the following:

I have a few problems. First:

import pylab as pl
import Image

im = Image.open('joconde.png')

pl.imshow(im)
pl.axis('off')
pl.show()

I get this:

Why is it rotated? That's not the point but I'd like to know why.

im_gray = im.convert('1')

pl.imshow(im_gray)
pl.show() 

And here is the processed black and white image:

Now everything looks working. But I need to use that image as a numpy array in order to do some image processing. All I have to do is this:

import numpy as np

im_arr = np.array(im_gray)

pl.imshow(im_arr)
pl.axis('off')
pl.show()

But I get this:

Why is this happening? I tried also:

im_arr = np.array(im_gray, dtype='float')

or:

im_arr = np.asarray(im_gray)

But nothing seems working. Maybe the problem is in the show method but I don't know.