title: grayscale gradient with skimage or numpy
body: <p>I have to create a linear grayscale gradient, with black shade on top and white shade at the bottom. I have to use skimage and numpy. </p>
  
  <p>I've found on scikit the code for a color linear gradient that goes horizontally instead of vertically here: <a href="http://scikit-image.org/docs/dev/auto_examples/plot_tinting_grayscale_images.html" rel="nofollow">http://scikit-image.org/docs/dev/auto_examples/plot_tinting_grayscale_images.html</a>.</p>
  
  <p>I would like an explanation of this code and some hints on how put everything in grayscale and vertical instead of colored and horizontal. Thanks!</p>