René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"imshow with very large arrays not working as expected","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\nHello, I am using `plt.imshow` to plot a very large array (~ 1 row x 150 million columns), and have noticed that the colors are not displayed properly.\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\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\n\r\n# Very large\r\narray = np.zeros(150000000, dtype=np.uint8)\r\narray[len(array) // 2:] = 1\r\nfig, ax = plt.subplots(figsize=(10, 3))\r\nim = ax.imshow(array.reshape(1, -1), vmin=0, vmax=1, aspect='auto')\r\nfig.colorbar(im, ax=ax)\r\n\r\n# 10x smaller\r\narray = np.zeros(15000000, dtype=np.uint8)\r\narray[len(array) // 2:] = 1\r\nfig, ax = plt.subplots(figsize=(10, 3))\r\nim = ax.imshow(array.reshape(1, -1), vmin=0, vmax=1, aspect='auto')\r\nfig.colorbar(im, ax=ax)\r\n```\r\n\r\n**Actual outcome**\r\nVery large\r\n![image](https://user-images.githubusercontent.com/1281521/104198905-cd836c80-53f4-11eb-8b31-932a30da23db.png)\r\n\r\n10x smaller\r\n![image](https://user-images.githubusercontent.com/1281521/104198876-c4929b00-53f4-11eb-93ba-a1e6b45dcd54.png)\r\n\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**Expected outcome**\r\nSince we set the later half of the array to 1 (and the rest is 0), we expect the image to change color at 75 million, but we see that all pixels are colored as 0.\r\n\r\n\r\n\u003c!--A description of the expected outcome from the code snippet--\u003e\r\n\u003c!--If this used to work in an earlier version of Matplotlib, please note the version it used to work on--\u003e\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: Ubuntu 20.04\r\n  * Matplotlib version: 3.3.2 (also tested on 3.3.3)\r\n  * Matplotlib backend: module://ipykernel.pylab.backend_inline\r\n  * Python version: 3.8.3 (also tested on 3.6.9)\r\n  * Jupyter version (if applicable):\r\n  * Other libraries: \r\n```\r\nipython                       7.18.1\r\nipython-genutils              0.2.0\r\njupyter                       1.0.0\r\njupyter-client                6.1.7\r\njupyter-console               6.2.0\r\njupyter-core                  4.6.3\r\njupyterlab                    2.2.8\r\njupyterlab-pygments           0.1.1\r\njupyterlab-server             1.2.0\r\n```\r\nPython installed via miniconda, but matplotlib was installed via pip.\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/Lioscro","@type":"Person","name":"Lioscro"},"datePublished":"2021-01-11T15:05:52.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":20},"url":"https://github.com/19276/matplotlib/issues/19276"}