diff --git a/galleries/examples/images_contours_and_fields/multi_image.py b/galleries/examples/images_contours_and_fields/multi_image.py index 5634a32abeb9..8be048055dec 100644 --- a/galleries/examples/images_contours_and_fields/multi_image.py +++ b/galleries/examples/images_contours_and_fields/multi_image.py @@ -1,9 +1,19 @@ """ -=============== -Multiple images -=============== +================================= +Multiple images with one colorbar +================================= -Make a set of images with a single colormap, norm, and colorbar. +Use a single colorbar for multiple images. + +Currently, a colorbar can only be connected to one image. The connection +guarantees that the data coloring is consistent with the colormap scale +(i.e. the color of value *x* in the colormap is used for coloring a data +value *x* in the image). + +If we want one colorbar to be representative for multiple images, we have +to explicitly ensure consistent data coloring by using the same data +normalization for all the images. We ensure this by explicitly creating a +``norm`` object that we pass to all the image plotting methods. """ import matplotlib.pyplot as plt @@ -12,47 +22,53 @@ from matplotlib import colors np.random.seed(19680801) -Nr = 3 -Nc = 2 -fig, axs = plt.subplots(Nr, Nc) +datasets = [ + (i+1)/10 * np.random.rand(10, 20) + for i in range(4) +] + +fig, axs = plt.subplots(2, 2) fig.suptitle('Multiple images') -images = [] -for i in range(Nr): - for j in range(Nc): - # Generate data with a range that varies from one plot to the next. - data = ((1 + i + j) / 10) * np.random.rand(10, 20) - images.append(axs[i, j].imshow(data)) - axs[i, j].label_outer() +# create a single norm to be shared across all images +norm = colors.Normalize(vmin=np.min(datasets), vmax=np.max(datasets)) -# Find the min and max of all colors for use in setting the color scale. -vmin = min(image.get_array().min() for image in images) -vmax = max(image.get_array().max() for image in images) -norm = colors.Normalize(vmin=vmin, vmax=vmax) -for im in images: - im.set_norm(norm) +images = [] +for ax, data in zip(axs.flat, datasets): + images.append(ax.imshow(data, norm=norm)) fig.colorbar(images[0], ax=axs, orientation='horizontal', fraction=.1) - -# Make images respond to changes in the norm of other images (e.g. via the -# "edit axis, curves and images parameters" GUI on Qt), but be careful not to -# recurse infinitely! -def update(changed_image): - for im in images: - if (changed_image.get_cmap() != im.get_cmap() - or changed_image.get_clim() != im.get_clim()): - im.set_cmap(changed_image.get_cmap()) - im.set_clim(changed_image.get_clim()) - - -for im in images: - im.callbacks.connect('changed', update) - plt.show() # %% +# The colors are now kept consistent across all images when changing the +# scaling, e.g. through zooming in the colorbar or via the "edit axis, +# curves and images parameters" GUI of the Qt backend. This is sufficient +# for most practical use cases. +# +# Advanced: Additionally sync the colormap +# ---------------------------------------- +# +# Sharing a common norm object guarantees synchronized scaling because scale +# changes modify the norm object in-place and thus propagate to all images +# that use this norm. This approach does not help with synchronizing colormaps +# because changing the colormap of an image (e.g. through the "edit axis, +# curves and images parameters" GUI of the Qt backend) results in the image +# referencing the new colormap object. Thus, the other images are not updated. +# +# To update the other images, sync the +# colormaps using the following code:: +# +# def sync_cmaps(changed_image): +# for im in images: +# if changed_image.get_cmap() != im.get_cmap(): +# im.set_cmap(changed_image.get_cmap()) +# +# for im in images: +# im.callbacks.connect('changed', sync_cmaps) +# # # .. admonition:: References # @@ -63,6 +79,4 @@ def update(changed_image): # - `matplotlib.figure.Figure.colorbar` / `matplotlib.pyplot.colorbar` # - `matplotlib.colors.Normalize` # - `matplotlib.cm.ScalarMappable.set_cmap` -# - `matplotlib.cm.ScalarMappable.set_norm` -# - `matplotlib.cm.ScalarMappable.set_clim` # - `matplotlib.cbook.CallbackRegistry.connect`