René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Switch to requiring Pillow rather than having our own png wrapper?","articleBody":"It looks like Pillow's png handling (which is hand-written https://github.com/python-pillow/Pillow/blob/master/src/PIL/PngImagePlugin.py, not based on libpng) is faster than matplotlib's, both for writing and for reading:\r\n```python\r\nfrom time import perf_counter\r\nimport matplotlib as mpl; mpl.use(\"agg\")\r\nfrom matplotlib import pyplot as plt\r\nimport numpy as np\r\nfrom PIL import Image\r\n\r\nfig, ax = plt.subplots()\r\nfig.canvas.draw()\r\nt = np.asarray(fig.canvas.renderer._renderer)\r\nfor writer in [\"mpl\", \"pil\"]:\r\n    print(f\"write with {writer}\")\r\n    start = perf_counter()\r\n    for _ in range(100):\r\n        mpl.image.imsave(\"/tmp/test.png\", t,\r\n                         pil_kwargs={\"mpl\": None, \"pil\": {}}[writer])\r\n    print(\"write\", perf_counter() - start)\r\n    start = perf_counter()\r\n    for _ in range(100):\r\n        mpl.image.imread(\"/tmp/test.png\")\r\n    print(\"mpl read\", perf_counter() - start)\r\n    start = perf_counter()\r\n    for _ in range(100):\r\n        with Image.open(\"/tmp/test.png\") as image:\r\n            mpl.image.pil_to_array(image)\r\n    print(\"pil read\", perf_counter() - start)\r\n```\r\nyields, for me:\r\n```\r\nwrite with mpl\r\nwrite 1.5242545299988706\r\nmpl read 0.9935761439992348\r\npil read 0.46841289500298444\r\nwrite with pil\r\nwrite 1.400021340996318\r\nmpl read 0.9913013100012904\r\npil read 0.4612834110012045\r\n```\r\n\r\nhttps://github.com/matplotlib/matplotlib/issues/15160 reminded me that it's not always trivial to get C-level dependencies set up before building (though that specific issue is about freetype).  We already vendor agg and qhull, and have an option to download freetype (via local_freetype/MPLLOCALFREETYPE), so the sole remaining dependency that always needs to be provided by the builder is libpng.\r\n\r\nIf we just depended (as an install_requires) on Pillow for png handling instead, we would be able to drop that dependency (together with a bunch of C code).  Pillow has wheels for all three major OSes, supports PyPy, is actively developed, and has been around for a very long time.\r\n\r\nThoughts on making the switch?","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2019-08-31T20:26:08.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/15165/matplotlib/issues/15165"}