title: Saving Matplotlib suface-plot with transparent background
body: <p>I try to save my 3d-Plot with an transparent background but with the transparent=True-Parameter of savefig it doesnt work. is there an other way to do it?</p>
  <p>Here is my actual attemp:</p>
  <pre><code>import matplotlib.pyplot as plt
  from matplotlib import cm
  from matplotlib.ticker import LinearLocator, FormatStrFormatter
  import numpy as np
  from scipy import interpolate
  
  
  Z = abs(p_r) #p_r = 2-dimensional complex valued numpy-Array (4x4) 
  
  X, Y = np.meshgrid(np.arange(-0.06, 0.07, 0.04), np.arange(-0.06, 0.07, 0.04))
  xnew, ynew = np.mgrid[-0.06:0.06:10j, -0.06:0.06:10j]
  tck = interpolate.bisplrep(X, Y, Z, s=0)
  znew = interpolate.bisplev(xnew[:,0], ynew[0,:], tck)
  
  fig = plt.figure()
  ax = fig.gca(projection='3d')
      
  surf = ax.plot_surface(xnew, ynew, znew,
                      cmap=cmap,linewidth=0, antialiased=False, shade=False)
  
  ax.set_zlim(0, 0.9)
  ax.zaxis.set_major_locator(LinearLocator(10))
  ax.zaxis.set_major_formatter(FormatStrFormatter('%.02f'))
  
  ax.set_xlabel('x [m]')
  ax.set_ylabel('y [m]')
  ax.set_zlabel('Amplitude [Pa]')
  
  plt.savefig(graphpath, tranparent=True)
  </code></pre>