title: Logarithmic colormap in matplotlib
body: <p>Is it possible to define a matplitlib colormap which logarithmically interpolates between two given colors?</p>
  
  <p><strong>Background:</strong> When plotting arrays in matplotlib via the <code>imshow(...)</code> command, <em>colormaps</em> are used to assign a color to each data value. Often, predefined colormaps are used from <code>matplotlib.cm</code> but also more enhanced colormaps can be created using <code>matplotlib.colors.LinearSegmentedColormap</code>. 
  Typically, in these colormaps the color value linearly changes with the data value.</p>
  
  <p><strong>Hint:</strong> My question is <strong><em>not</em></strong>, how to plot an array logarithmically. This is usually done, by keeping the linear colormap and some tricks (either by plotting <code>log(array)</code> and replacing the labels <code>x</code> on the colorbar by <code>10^x</code>, or by explicitly changing the normalization behavior of the plot command). Here, I explicitly need the colormap instance.</p>