[Matplotlib-users] Change a few pixels color

Hi,

Imagine you have this code:

import  numpy  as  np
import  matplotlib.cm  as  cm
import  matplotlib.mlab  as  mlab
import  matplotlib.pyplot  as  plt

delta  =  0.25
x  =  y  =  np.arange(-3.0,  3.0,  delta)
X,  Y  =  np.meshgrid(x,  y)
Z1  =  mlab.bivariate_normal(X,  Y,  1.0,  1.0,  0.0,  0.0)
Z2  =  mlab.bivariate_normal(X,  Y,  1.5,  0.5,  1,  1)
Z  =  Z2-Z1   # difference of Gaussians

plt.imshow(Z,  interpolation='nearest',  cmap=cm.gray,  origin='lower',  extent=[-3,3,-3,3])

Then you want to change the color of a few pixels to red.
You have a list of coordinates (i,j) and each pixel in this list should 
now be red.

I could play with masked arrays like in:
http://matplotlib.sourceforge.net/examples/pylab_examples/image_masked.html
but I would prefer a simple "display this pixel (i,j) in red whatever 
his value is" function.

Xavier