René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"imshow with LogNorm crashes with certain inputs","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\nDue to changes introduced in 3dea5c7, trying to display some images with LogNorm will crash because vmin gets auto-adjusted to 0 (which is invalid for LogNorm).\r\n\r\n**Code for reproduction**\r\n\r\n```python\r\n\r\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\nfrom matplotlib.colors import LogNorm\r\n\r\ndata = np.full((500, 500), -1, dtype=np.float64)\r\ndata[0:250, :] = 1E20\r\n\r\nfig, ax = plt.subplots()\r\nim = ax.imshow(data, norm=LogNorm(vmin=100, vmax=data.max()))\r\n\r\nplt.show()\r\n```\r\n\r\n**Actual outcome**\r\n\r\n\u003c!--The output produced by the above code, which may be a screenshot, console output, etc.--\u003e\r\n\r\n```\r\n  File \"C:\\Python38\\lib\\site-packages\\matplotlib\\image.py\", line 922, in make_image\r\n    return self._make_image(self._A, bbox, transformed_bbox, clip,\r\n  File \"C:\\Python38\\lib\\site-packages\\matplotlib\\image.py\", line 541, in _make_image\r\n    output = self.norm(resampled_masked)\r\n  File \"C:\\Python38\\lib\\site-packages\\matplotlib\\colors.py\", line 1193, in __call__\r\n    self._check_vmin_vmax()\r\n  File \"C:\\Python38\\lib\\site-packages\\matplotlib\\colors.py\", line 1182, in _check_vmin_vmax\r\n    raise ValueError(\"minvalue must be positive\")\r\nValueError: minvalue must be positive\r\n```\r\n\r\n**Expected outcome**\r\n\r\nShowed a plot in MPL 3.1 (and I believe every version until 3.3). The crash is coming from _make_image transforming vmin to be zero per changes added in 3dea5c7. I guess perhaps the solution is \"then don't try to plot that, use a vmin closer to your vmax\" but kind of inconvenient for code that previously worked fine.\r\n\r\n**Matplotlib version**:  3.3.1","author":{"url":"https://github.com/LevN0","@type":"Person","name":"LevN0"},"datePublished":"2020-09-06T18:05:18.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/18415/matplotlib/issues/18415"}