René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: imshow uint8 image with colors.NoNorm() causes OverflowError when mousing over figure","articleBody":"### Bug summary\n\nI'm displaying a uint8 image, intending to show the actual values in the image (i.e. no min-max scaling as is the default). Specifying `colors.NoNorm()` as the `norm` argument is I think the recommended way to do this. The image is shown correctly. But when mousing over the image the terminal window is filled with:\n```none\nTraceback (most recent call last):\n  File \"/opt/homebrew/lib/python3.14/site-packages/matplotlib/cbook.py\", line 361, in process\n    func(*args, **kwargs)\n    ~~~~^^^^^^^^^^^^^^^^^\n  File \"/opt/homebrew/lib/python3.14/site-packages/matplotlib/backend_bases.py\", line 2956, in mouse_move\n    self.set_message(self._mouse_event_to_message(event))\n                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^\n  File \"/opt/homebrew/lib/python3.14/site-packages/matplotlib/backend_bases.py\", line 2948, in _mouse_event_to_message\n    data_str = a.format_cursor_data(data).rstrip()\n               ~~~~~~~~~~~~~~~~~~~~^^^^^^\n  File \"/opt/homebrew/lib/python3.14/site-packages/matplotlib/artist.py\", line 1354, in format_cursor_data\n    return self._format_cursor_data_override(data)\n           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^\n  File \"/opt/homebrew/lib/python3.14/site-packages/matplotlib/colorizer.py\", line 498, in _format_cursor_data_override\n    (int(normed * n) + np.array([0, 1])) / n)\n         ~~~~~~~^~~\nOverflowError: Python integer 256 out of bounds for uint8\n```\nI am assuming this is caused by the code that writes pixel values in the bottom-right corner of the figure window.\n\n### Code for reproduction\n\n```Python\nimport matplotlib\nimport matplotlib.pyplot as plt\nimport numpy as np\n\nimg = np.tile(np.arange(100, dtype=np.uint8), (100, 1))\nplt.imshow(img, norm=matplotlib.colors.NoNorm())\nplt.show()\n```\n\n### Actual outcome\n\nThe terminal is filled with repeated OverflowError messages as shown above.\n\n### Expected outcome\n\nNo error messages.\n\n### Additional information\n\nThis did not happen when I originally wrote my code 9 years ago. I can't be sure, but I think this is a fairly recent regression.\n\n### Operating system\n\nmacOS\n\n### Matplotlib Version\n\n3.10.9 and 3.11.0\n\n### Matplotlib Backend\n\nmacosx\n\n### Python version\n\n3.14.5\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\npip","author":{"url":"https://github.com/crisluengo","@type":"Person","name":"crisluengo"},"datePublished":"2026-06-27T12:02:28.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/31960/matplotlib/issues/31960"}