set aspect ratio

[mgkuhn]

The aspect kwarg to imshow() currently appears to support only the values

• :none, which sets the aspect ratio of pixels automatically such that the window is kept filled as it is resized, and
• :auto (or any other value really), which sets the aspect ratio of pixels to 1 (square pixels).

If I have an image with non-square pixels of a known aspect ratio, e.g. where the horizontal resolution is 1.6 times the vertical resolution, it would be useful to be able to specify a numeric aspect ratio (either for the entire image or for one pixel).