René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"imshow doesn't normalize the color range in RGB images ","articleBody":"### ` imshow` doesn't normalize the color range in RGB images\r\n\r\n**Bug summary**\r\nWhen single channel float image is passed to `imshow` it gets normalized to range [0,1] before display. This does not happen for RGB images.\r\n\r\n**Code for reproduction**\r\n```python\r\nimg = np.arange(0, 0.6, .1).reshape(6,1)\r\nplt.subplot(141)\r\nplt.title('grayscale')\r\nplt.imshow(img)\r\nplt.colorbar()\r\n\r\nimg = np.arange(0, 0.6, .1).repeat(3).reshape(6,1,3)\r\nplt.subplot(142)\r\nplt.title('RGB')\r\nplt.imshow(img)\r\nplt.colorbar()\r\n\r\nimg = np.arange(0, 1.6, .2).reshape(8,1)\r\nplt.subplot(143)\r\nplt.title('grayscale')\r\nplt.imshow(img)\r\nplt.colorbar()\r\n\r\nimg = np.arange(0, 1.6, .2).repeat(3).reshape(8,1,3)\r\nplt.subplot(144)\r\nplt.title('RGB')\r\nplt.imshow(img)\r\nplt.colorbar()\r\n```\r\n\r\n**Actual outcome**\r\n![mpl_color_norm](https://user-images.githubusercontent.com/4110525/31547015-02a1d7ce-b026-11e7-9339-614ea8642898.png)\r\nPlease also note how the colorbars are misleading.\r\n\r\n**Expected outcome**\r\nI'd expect the RGB images to look the same as grayscale.\r\n\r\n**Real life example**\r\nThis is how I encountered this issue. What is the value in all three channels at [3,18]? It is actually around 1.2!\r\n![download](https://user-images.githubusercontent.com/4110525/31547169-a0b7f52e-b026-11e7-989b-2c3e35d4c595.png)\r\n\r\n**Matplotlib version: 2.0.2**\r\n\r\n**Discussion**\r\nThe same issue: #5382 , [on SO](https://stackoverflow.com/questions/24739769/matplotlib-imshow-plots-different-if-using-colormap-or-rgb-array), and [another SO](https://stackoverflow.com/questions/39925420/bizzare-matplotlib-behaviour-in-displaying-images-cast-as-floats).\r\n\r\nIn #5382 @tacaswell  explains that  and RGB image \"goes through a different code path which do not get passed through the normalize/colormap framework\". Colormapping of course makes no sense for color images but I believe that normalization should be consistently applied to RGB images.\r\n\r\nI got used to matplotlib normalization of single channel float images and the need of using `vmin` and `vmax` to avoid this normalization and intuitively expected RGB images to be treated consistently. As I noticed subsequently the docstrigs say that \"the value for each component of MxNx3 and MxNx4 float arrays should be in the range 0.0 to 1.0.\" But I believe that to simply overflow without raising error or warning is not correct.\r\n\r\n","author":{"url":"https://github.com/michalkahle","@type":"Person","name":"michalkahle"},"datePublished":"2017-10-13T13:57:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":26},"url":"https://github.com/9391/matplotlib/issues/9391"}