René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"I broke imshow(\u003csigned integer array\u003e) :-(","articleBody":"mpl2.0b3\n\n```\nIn [4]: plt.imshow(np.random.randint(-128, 128, dtype=np.int8, size=(3, 3)))\nOut[4]: \u003cmatplotlib.image.AxesImage at 0x7fe00ba2f0f0\u003e\n\nIn [5]: /usr/lib/python3.5/site-packages/matplotlib/colors.py:848: RuntimeWarning: overflow encos\n  resdat /= (vmax - vmin)\n```\n\nand a fully black image appears.\n\nPretty sure this is due to #6700 and can be fixed by restoring the casts of vmin and vmax to a floating type.  However that type should be determined as in `process_value` (i.e., `np.float32 if dtype.itemsize \u003c= 2 else np.promote_types(dtype, float)` -- see the issue for the discussion).\n\nNot making a PR yet because this (as well as the original #6700) may or may not affect the other Normalize classes too?  Perhaps that's something that should be factored out.\n","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2016-07-24T23:31:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/6825/matplotlib/issues/6825"}