René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"PIL-opened image and imread-opened image render slightly differently in classic mode","articleBody":"\u003c!--To help us understand and resolve your issue, please fill out the form to the best of your ability.--\u003e\r\n\u003c!--You can feel free to delete the sections that do not apply.--\u003e\r\n\r\n### Bug report\r\n\r\n**Bug summary**\r\n\r\nPer the title.\r\n\r\n**Code for reproduction**\r\n\r\n\u003c!--A minimum code snippet required to reproduce the bug.\r\nPlease make sure to minimize the number of dependencies required, and provide\r\nany necessary plotted data.\r\nAvoid using threads, as Matplotlib is (explicitly) not thread-safe.--\u003e\r\n\r\n```python\r\nfrom pathlib import Path\r\nimport matplotlib as mpl\r\nfrom matplotlib.testing.compare import compare_images\r\nfrom matplotlib import pyplot as plt, style\r\nfrom PIL import Image\r\n\r\nmpl.use(\"agg\")\r\nmpl.style.use(\"classic\")\r\n\r\npath = str(Path(mpl.__file__).parent / \"tests/baseline_images/pngsuite/basn3p04.png\")\r\n\r\nfig = plt.figure()\r\nfig.subplots().imshow(plt.imread(path))\r\nfig.savefig(\"1.png\")\r\nfig = plt.figure()\r\nfig.subplots().imshow(Image.open(path))\r\nfig.savefig(\"2.png\")\r\nprint(compare_images(\"1.png\", \"2.png\", tol=0))\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\nError: Image files did not match.\r\n  RMS Value: 0.010865337342004415\r\n  Expected:  \r\n    1.png\r\n  Actual:    \r\n    2.png\r\n  Difference:\r\n    2-failed-diff.png\r\n  Tolerance: \r\n    0\r\n```\r\n\r\n**Expected outcome**\r\n\r\nNo diff.\r\n\r\nI *think* this may possibly(???) be due to rounding errors when imread converts from 0-255 (uint8) to 0-1 (float) and then imshow converts back to 0-255 (uint8)?\r\n\r\nNote that this does not occur when using the mpl20 default style.\r\n\r\n**Matplotlib version**\r\n\u003c!--Please specify your platform and versions of the relevant libraries you are using:--\u003e\r\n  * Operating system: linux\r\n  * Matplotlib version: master\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): agg\r\n  * Python version: 3.7\r\n  * Jupyter version (if applicable):\r\n  * Other libraries: \r\n\r\n\u003c!--Please tell us how you installed matplotlib and python e.g., from source, pip, conda--\u003e\r\n\u003c!--If you installed from conda, please specify which channel you used if not the default--\u003e\r\n\r\n","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2019-05-27T09:49:58.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/14340/matplotlib/issues/14340"}