title: matplotlib.pyplot.imsave backend
body: <p>I'm working in Spyder with matplotlib.pyplot and want to save numpy array to images.
  The documentation of imsave() says, that the format to which I can save depends on the backend. So what exactly is the backend? I seem to be able to save .tiff images, but f.e. I want them to be saved as 8-bit tiffs instead of RGB-Tiffs. Any Idea where I can change that?</p>