nonuniform meshes

Can matplotlib do image plots of a nonuniform mesh?

from matplotlib.matlab import *

x=array([0.,0.5,0.51,4.])
y=array([0.,1.])
X,Y = meshgrid(x,y)
Z=array([[0,1,1,2],[0,1,1,2]])
im = imshow(Z,cmap=cm.jet)
show()

thanks, Randy