Reported by Jean-Luc:  SparseNoise seems broken in his version of numpy:

imagen/imagen/random.pyc in_distrib(self, shape, p)
    483                  x=  p.random_generator.randint(0,  n)
    484                  y=  p.random_generator.randint(0,  n)
--> 485                  z  =  p.random_generator.choice([-1,1])
    486                  Z[x,y]  =  z
    487

AttributeError: 'mtrand.RandomState' object has no attribute 'choice'