>>> """
======================================
Thresholding an Image with RangeSlider
======================================

Using the RangeSlider widget to control the thresholding of an image.

The RangeSlider widget can be used similarly to the `.widgets.Slider`
widget. The major difference is that RangeSlider's ``val`` attribute
is a tuple of floats ``(lower val, upper val)`` rather than a single float.

See :doc:`/gallery/widgets/slider_demo` for an example of using
a ``Slider`` to control a single float.

See :doc:`/gallery/widgets/slider_snap_demo` for an example of having
the ``Slider`` snap to discrete values.
"""
... 
... import numpy as np
... import matplotlib.pyplot as plt
... from matplotlib.widgets import RangeSlider
... 
... # generate a fake image
... np.random.seed(19680801)
... N = 128
... img = np.random.randn(N, N)
... 
... fig, axs = plt.subplots(1, 2, figsize=(10, 5))
... plt.subplots_adjust(bottom=0.25)
... 
... im = axs[0].imshow(img)
... axs[1].hist(img.flatten(), bins='auto')
... axs[1].set_title('Histogram of pixel intensities')
... 
... # Create the RangeSlider
... slider_ax = plt.axes([0.20, 0.1, 0.60, 0.03])
... slider = RangeSlider(slider_ax, "Threshold", img.min(), img.max())
... 
... # Create the Vertical lines on the histogram
... lower_limit_line = axs[1].axvline(slider.val[0], color='k')
... upper_limit_line = axs[1].axvline(slider.val[1], color='k')
... 
... 
... def update(val):
...     # The val passed to a callback by the RangeSlider will
...     # be a tuple of (min, max)
... 
...     # Update the image's colormap
...     im.norm.vmin = val[0]
...     im.norm.vmax = val[1]
... 
...     # Update the position of the vertical lines
...     lower_limit_line.set_xdata([val[0], val[0]])
...     upper_limit_line.set_xdata([val[1], val[1]])
... 
...     # Redraw the figure to ensure it updates
...     fig.canvas.draw_idle()
... 
... 
... slider.on_changed(update)
... plt.show()
... 
... #############################################################################
... #
... # .. admonition:: References
... #
... #    The use of the following functions, methods, classes and modules is shown
... #    in this example:
... #
... #    - `matplotlib.widgets.RangeSlider`
...