``imshow`` *interpolation_stage* default changed to 'auto'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The *interpolation_stage* parameter of  `~.Axes.imshow` has a new default
value 'auto'.  For images that are up-sampled less than a factor of
three or down-sampled, image interpolation will occur in 'rgba' space.  For images
that are up-sampled by a factor of 3 or more, then image interpolation occurs
in 'data' space.

The previous default was 'data', so down-sampled images may change subtly with
the new default.  However, the new default also avoids floating point artifacts
at sharp boundaries in a colormap when down-sampling.

The previous behavior can achieved by setting the *interpolation_stage* parameter
or :rc:`image.interpolation_stage` to 'data'.

imshow default *interpolation* changed to 'auto'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The *interpolation* parameter of `~.Axes.imshow` has a new default
value 'auto', changed from 'antialiased', for consistency with *interpolation_stage*
and because the interpolation is only anti-aliasing during down-sampling.  Passing
'antialiased' still works, and behaves exactly the same as 'auto', but is discouraged.
