PR Summary

When switching norms of the mappable we should autoscale the norm using the data if possible rather than setting it to (0, 1). From the linked issue, this currently errors due to vmin=0 when updating the norm, even though the data is all valid for LogNorm.

import matplotlib.pyplot as plt
from matplotlib.colors import LogNorm, Normalize
import numpy as np

img = np.arange(1, 11).reshape((2, 5))

fig, ax = plt.subplots(1, 1)
plot = ax.imshow(img, cmap='gray')
cb = fig.colorbar(plot, ax=ax)
plot.norm = LogNorm()
plt.show()

closes #5424

PR Checklist

Documentation and Tests

• Has pytest style unit tests (and pytest passes)
• [-] Documentation is sphinx and numpydoc compliant (the docs should build without error).
• [-] New plotting related features are documented with examples.

Release Notes

• [-] New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• [-] API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• [-] Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst