title: Matplotlib plot_surface transparency artefact
body: <p>I'm trying to plot a surface in 3D from a set of data which specifies the z-values. I get some weird transparency artefact though, where I can see through the surface, even though I set alpha=1.0.</p>
  
  <p>The artefact is present both when plotting and when saved to file (both as png and pdf):
  <a href="https://i.stack.imgur.com/2bXbI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/2bXbI.png" alt="enter image description here"></a></p>
  
  <p>I have tried changing the line width, and changing the number of strides from 1 to 10 (in the latter case, the surface is not visible though due to too rough resolution).</p>
  
  <p><strong>Q: How can I get rid of this transparency?</strong></p>
  
  <p>Here is my code:</p>
  
  <pre><code>import sys
  import numpy as np
  import numpy.ma as ma
  import matplotlib as mpl
  import matplotlib.pyplot as plt
  from mpl_toolkits.mplot3d import Axes3D
  
  y_label = r'x'
  x_label = r'y'
  z_label = r'z'
  
  x_scale = 2.0*np.pi
  y_scale = 2.0*np.pi
  
  y_numPoints = 250
  x_numPoints = 250
  
  def quasiCrystal(x, y):
      z = 0
      for i in range(0,5):
          z += np.sin(x * np.cos(float(i)*np.pi/5.0) +
                      y * np.sin(float(i)*np.pi/5.0))
      return z
  
  x = np.linspace(-x_scale, x_scale, x_numPoints)
  y = np.linspace(-y_scale, y_scale, y_numPoints)
  X,Y = np.meshgrid(x,y)
  
  Z = quasiCrystal(X, Y)
  
  
  f = plt.figure()
  ax = f.gca(projection='3d')
  
  surf = ax.plot_surface( X, Y, Z,
                          rstride=5, cstride=5,
                          cmap='seismic',
                          alpha=1,
                          linewidth=0,
                          antialiased=True,
                          vmin=np.min(Z),
                          vmax=np.max(Z)
                        )
  
  ax.set_zlim3d(np.min(Z), np.max(Z))
  
  f.colorbar(surf, label=z_label)
  
  ax.set_xlabel(x_label)
  ax.set_ylabel(y_label)
  ax.set_zlabel(z_label)
  
  plt.show()
  </code></pre>
  
  <p>Here is another picture of my actual data where it is easier to see the artefact:
  <a href="https://i.stack.imgur.com/nXivZ.png" rel="noreferrer"><img src="https://i.stack.imgur.com/nXivZ.png" alt="enter image description here"></a></p>