That's the problem, I believe. 'imread' in mpl always reads
> images in as MxNx4, while Matlab will check if the image is
> B&W and just do MxN. Is there any way to force MxN behaviour
> in mpl?
No way currently, but one could modify the png reader to do it....
Probably easiest is to use PIL and get a grayscale numpy array out,
then mpl's colormapping and normalization will work as advertised.