René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"issue with transparency in imshow","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\nHi, I am trying to understand the following example on how to provide an array-like alpha in imshow.\r\n\r\nhttps://matplotlib.org/3.2.0/gallery/images_contours_and_fields/image_transparency_blend.html\r\n\r\nHowever, the exact same script gives me following errors. What is the source of this bug?\r\n\r\n**Bug summary**\r\n\r\nValueError: operands could not be broadcast together with shapes (218,218) (100,100)\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```\r\n\r\ndef normal_pdf(x, mean, var):\r\n    return np.exp(-(x - mean)**2 / (2*var))\r\n\r\n# Generate the space in which the blobs will live\r\nxmin, xmax, ymin, ymax = (0, 100, 0, 100)\r\nn_bins = 100\r\nxx = np.linspace(xmin, xmax, n_bins)\r\nyy = np.linspace(ymin, ymax, n_bins)\r\n\r\n# Generate the blobs. The range of the values is roughly -.0002 to .0002\r\nmeans_high = [20, 50]\r\nmeans_low = [50, 60]\r\nvar = [150, 200]\r\n\r\ngauss_x_high = normal_pdf(xx, means_high[0], var[0])\r\ngauss_y_high = normal_pdf(yy, means_high[1], var[0])\r\n\r\ngauss_x_low = normal_pdf(xx, means_low[0], var[1])\r\ngauss_y_low = normal_pdf(yy, means_low[1], var[1])\r\n\r\nweights = (np.outer(gauss_y_high, gauss_x_high) - np.outer(gauss_y_low, gauss_x_low))\r\n\r\n# We'll also create a grey background into which the pixels will fade\r\n#greys = np.full((*weights.shape, 3), 70, dtype=np.uint8)\r\n\r\n# First we'll plot these blobs using ``imshow`` without transparency.\r\nvmax = np.abs(weights).max()\r\nimshow_kwargs = {\r\n    'vmax': vmax,\r\n    'vmin': -vmax,\r\n    'cmap': 'RdYlBu',\r\n    'extent': (xmin, xmax, ymin, ymax),\r\n}\r\n\r\nfig, ax = plt.subplots()\r\n#ax.imshow(greys)\r\nax.imshow(weights, **imshow_kwargs)\r\nax.set_axis_off()\r\n\r\n# Create an alpha channel of linearly increasing values moving to the right.\r\nalphas = np.ones(weights.shape)\r\nalphas[:, 30:] = np.linspace(1, 0, 70)\r\n\r\n# Create the figure and image\r\n# Note that the absolute values may be slightly different\r\nfig, ax = plt.subplots()\r\n#ax.imshow(greys)\r\nax.imshow(weights, alpha=alphas, **imshow_kwargs)\r\nax.set_axis_off()\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\n# If applicable, paste the console output here\r\n#\r\n#\r\n```\r\n```\r\nError in callback \u003cfunction post_execute at 0x7f4972d48578\u003e (for post_execute):\r\n---------------------------------------------------------------------------\r\nValueError                                Traceback (most recent call last)\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/pyplot.pyc in post_execute()\r\n    147             def post_execute():\r\n    148                 if matplotlib.is_interactive():\r\n--\u003e 149                     draw_all()\r\n    150 \r\n    151             # IPython \u003e= 2\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/_pylab_helpers.pyc in draw_all(cls, force)\r\n    134         for f_mgr in cls.get_all_fig_managers():\r\n    135             if force or f_mgr.canvas.figure.stale:\r\n--\u003e 136                 f_mgr.canvas.draw_idle()\r\n    137 \r\n    138 atexit.register(Gcf.destroy_all)\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/backend_bases.pyc in draw_idle(self, *args, **kwargs)\r\n   2053         if not self._is_idle_drawing:\r\n   2054             with self._idle_draw_cntx():\r\n-\u003e 2055                 self.draw(*args, **kwargs)\r\n   2056 \r\n   2057     def draw_cursor(self, event):\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/backends/backend_agg.pyc in draw(self)\r\n    435             # if toolbar:\r\n    436             #     toolbar.set_cursor(cursors.WAIT)\r\n--\u003e 437             self.figure.draw(self.renderer)\r\n    438             # A GUI class may be need to update a window using this draw, so\r\n    439             # don't forget to call the superclass.\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs)\r\n     53                 renderer.start_filter()\r\n     54 \r\n---\u003e 55             return draw(artist, renderer, *args, **kwargs)\r\n     56         finally:\r\n     57             if artist.get_agg_filter() is not None:\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/figure.pyc in draw(self, renderer)\r\n   1491 \r\n   1492             mimage._draw_list_compositing_images(\r\n-\u003e 1493                 renderer, self, artists, self.suppressComposite)\r\n   1494 \r\n   1495             renderer.close_group('figure')\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)\r\n    139     if not_composite or not has_images:\r\n    140         for a in artists:\r\n--\u003e 141             a.draw(renderer)\r\n    142     else:\r\n    143         # Composite any adjacent images together\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs)\r\n     53                 renderer.start_filter()\r\n     54 \r\n---\u003e 55             return draw(artist, renderer, *args, **kwargs)\r\n     56         finally:\r\n     57             if artist.get_agg_filter() is not None:\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/axes/_base.pyc in draw(self, renderer, inframe)\r\n   2633             renderer.stop_rasterizing()\r\n   2634 \r\n-\u003e 2635         mimage._draw_list_compositing_images(renderer, self, artists)\r\n   2636 \r\n   2637         renderer.close_group('axes')\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)\r\n    139     if not_composite or not has_images:\r\n    140         for a in artists:\r\n--\u003e 141             a.draw(renderer)\r\n    142     else:\r\n    143         # Composite any adjacent images together\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs)\r\n     53                 renderer.start_filter()\r\n     54 \r\n---\u003e 55             return draw(artist, renderer, *args, **kwargs)\r\n     56         finally:\r\n     57             if artist.get_agg_filter() is not None:\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in draw(self, renderer, *args, **kwargs)\r\n    592         else:\r\n    593             im, l, b, trans = self.make_image(\r\n--\u003e 594                 renderer, renderer.get_image_magnification())\r\n    595             if im is not None:\r\n    596                 renderer.draw_image(gc, l, b, im)\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in make_image(self, renderer, magnification, unsampled)\r\n    840         return self._make_image(\r\n    841             self._A, bbox, transformed_bbox, self.axes.bbox, magnification,\r\n--\u003e 842             unsampled=unsampled)\r\n    843 \r\n    844     def _check_unsampled_image(self, renderer):\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification, unsampled, round_to_pixel_border)\r\n    520                 alpha_channel = output[:, :, 3]\r\n    521                 alpha_channel[:] = np.asarray(\r\n--\u003e 522                     np.asarray(alpha_channel, np.float32) * out_alpha * alpha,\r\n    523                     np.uint8)\r\n    524 \r\n\r\nValueError: operands could not be broadcast together with shapes (218,218) (100,100) \r\n\r\n---------------------------------------------------------------------------\r\nValueError                                Traceback (most recent call last)\r\n/xxx/anaconda2/lib/python2.7/site-packages/IPython/core/formatters.pyc in __call__(self, obj)\r\n    332                 pass\r\n    333             else:\r\n--\u003e 334                 return printer(obj)\r\n    335             # Finally look for special method names\r\n    336             method = get_real_method(obj, self.print_method)\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/IPython/core/pylabtools.pyc in \u003clambda\u003e(fig)\r\n    245 \r\n    246     if 'png' in formats:\r\n--\u003e 247         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))\r\n    248     if 'retina' in formats or 'png2x' in formats:\r\n    249         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/IPython/core/pylabtools.pyc in print_figure(fig, fmt, bbox_inches, **kwargs)\r\n    129 \r\n    130     bytes_io = BytesIO()\r\n--\u003e 131     fig.canvas.print_figure(bytes_io, **kw)\r\n    132     data = bytes_io.getvalue()\r\n    133     if fmt == 'svg':\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/backend_bases.pyc in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, **kwargs)\r\n   2210                     orientation=orientation,\r\n   2211                     dryrun=True,\r\n-\u003e 2212                     **kwargs)\r\n   2213                 renderer = self.figure._cachedRenderer\r\n   2214                 bbox_inches = self.figure.get_tightbbox(renderer)\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/backends/backend_agg.pyc in print_png(self, filename_or_obj, *args, **kwargs)\r\n    515 \r\n    516     def print_png(self, filename_or_obj, *args, **kwargs):\r\n--\u003e 517         FigureCanvasAgg.draw(self)\r\n    518         renderer = self.get_renderer()\r\n    519         original_dpi = renderer.dpi\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/backends/backend_agg.pyc in draw(self)\r\n    435             # if toolbar:\r\n    436             #     toolbar.set_cursor(cursors.WAIT)\r\n--\u003e 437             self.figure.draw(self.renderer)\r\n    438             # A GUI class may be need to update a window using this draw, so\r\n    439             # don't forget to call the superclass.\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs)\r\n     53                 renderer.start_filter()\r\n     54 \r\n---\u003e 55             return draw(artist, renderer, *args, **kwargs)\r\n     56         finally:\r\n     57             if artist.get_agg_filter() is not None:\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/figure.pyc in draw(self, renderer)\r\n   1491 \r\n   1492             mimage._draw_list_compositing_images(\r\n-\u003e 1493                 renderer, self, artists, self.suppressComposite)\r\n   1494 \r\n   1495             renderer.close_group('figure')\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)\r\n    139     if not_composite or not has_images:\r\n    140         for a in artists:\r\n--\u003e 141             a.draw(renderer)\r\n    142     else:\r\n    143         # Composite any adjacent images together\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs)\r\n     53                 renderer.start_filter()\r\n     54 \r\n---\u003e 55             return draw(artist, renderer, *args, **kwargs)\r\n     56         finally:\r\n     57             if artist.get_agg_filter() is not None:\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/axes/_base.pyc in draw(self, renderer, inframe)\r\n   2633             renderer.stop_rasterizing()\r\n   2634 \r\n-\u003e 2635         mimage._draw_list_compositing_images(renderer, self, artists)\r\n   2636 \r\n   2637         renderer.close_group('axes')\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)\r\n    139     if not_composite or not has_images:\r\n    140         for a in artists:\r\n--\u003e 141             a.draw(renderer)\r\n    142     else:\r\n    143         # Composite any adjacent images together\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/artist.pyc in draw_wrapper(artist, renderer, *args, **kwargs)\r\n     53                 renderer.start_filter()\r\n     54 \r\n---\u003e 55             return draw(artist, renderer, *args, **kwargs)\r\n     56         finally:\r\n     57             if artist.get_agg_filter() is not None:\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in draw(self, renderer, *args, **kwargs)\r\n    592         else:\r\n    593             im, l, b, trans = self.make_image(\r\n--\u003e 594                 renderer, renderer.get_image_magnification())\r\n    595             if im is not None:\r\n    596                 renderer.draw_image(gc, l, b, im)\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in make_image(self, renderer, magnification, unsampled)\r\n    840         return self._make_image(\r\n    841             self._A, bbox, transformed_bbox, self.axes.bbox, magnification,\r\n--\u003e 842             unsampled=unsampled)\r\n    843 \r\n    844     def _check_unsampled_image(self, renderer):\r\n\r\n/xxx/anaconda2/lib/python2.7/site-packages/matplotlib/image.pyc in _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification, unsampled, round_to_pixel_border)\r\n    520                 alpha_channel = output[:, :, 3]\r\n    521                 alpha_channel[:] = np.asarray(\r\n--\u003e 522                     np.asarray(alpha_channel, np.float32) * out_alpha * alpha,\r\n    523                     np.uint8)\r\n    524 \r\n\r\nValueError: operands could not be broadcast together with shapes (218,218) (100,100)\r\n```\r\n\r\n**Expected outcome**\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: \r\n  * Matplotlib version: 2.2.3\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): TkAgg\r\n  * Python version: 2.7.16\r\n  * Jupyter notebook version (if applicable): 5.7.8\r\n  * Other libraries: Numpy version: 1.16.5\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/pink2289","@type":"Person","name":"pink2289"},"datePublished":"2020-03-11T10:54:17.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/16730/matplotlib/issues/16730"}