equal to 1. If
    the `metric` is equal to 'chessboard', a `metric` is generated
    using `generate_binary_structure` with a squared distance equal to
    the dimensionality of the array. These choices correspond to the
    common interpretations of the 'taxicab' and the 'chessboard'
    distance metrics in two dimensions.
    A custom metric may be provided, in the form of a matrix where
    each dimension has a length of three.
    'cityblock' and 'manhattan' are also valid, and map to 'taxicab'.
    The default is 'chessboard'.
return_distances : bool, optional
    Whether to calculate the distance transform.
    Default is True.
return_indices : bool, optional
    Whether to calculate the feature transform.
    Default is False.
distances : int32 ndarray, optional
    An output array to store the calculated distance transform, instead of
    returning it.
    `return_distances` must be True.
    It must be the same shape as `input`.
indices : int32 ndarray, optional
    An output array to store the calculated feature transform, instead of
    returning it.
    `return_indicies` must be True.
    Its shape must be ``(input.ndim,) + input.shape``.

Returns
-------
distances : int32 ndarray, optional
    The calculated distance transform. Returned only when
    `return_distances` is True, and `distances` is not supplied.
    It will have the same shape as the input array.
indices : int32 ndarray, optional
    The calculated feature transform. It has an input-shaped array for each
    dimension of the input. See distance_transform_edt documentation for an
    example.
    Returned only when `return_indices` is True, and `indices` is not
    supplied.

See Also
--------
distance_transform_edt : Fast distance transform for euclidean metric
distance_transform_bf : Distance transform for different metrics using
                        a slower brute force algorithm

Examples
--------
Import the necessary modules.

>>> import numpy as np
>>> from scipy.ndimage import distance_transform_cdt
>>> import matplotlib.pyplot as plt
>>> from mpl_toolkits.axes_grid1 import ImageGrid

First, we create a toy binary image.

>>> def add_circle(center_x, center_y, radius, image, fillvalue=1):
...     # fill circular area with 1
...     xx, yy = np.mgrid[:image.shape[0], :image.shape[1]]
...     circle = (xx - center_x) ** 2 + (yy - center_y) ** 2
...     circle_shape = np.sqrt(circle) < radius
...     image[circle_shape] = fillvalue
...     return image
>>> image = np.zeros((100, 100), dtype=np.uint8)
>>> image[35:65, 20:80] = 1
>>> image = add_circle(28, 65, 10, image)
>>> image = add_circle(37, 30, 10, image)
>>> image = add_circle(70, 45, 20, image)
>>> image = add_circle(45, 80, 10, image)

Next, we set up the figure.

>>> fig = plt.figure(figsize=(5, 15))
>>> grid = ImageGrid(fig, 111, nrows_ncols=(3, 1), axes_pad=(0.5, 0.3),
...                  label_mode="1", share_all=True,
...                  cbar_location="right", cbar_mode="each",
...                  cbar_size="7%", cbar_pad="2%")
>>> for ax in grid:
...     ax.axis('off')
>>> top, middle, bottom = grid
>>> colorbar_ticks = [0, 10, 20]

The top image contains the original binary image.

>>> binary_image = top.imshow(image, cmap='gray')
>>> cbar_binary_image = top.cax.colorbar(binary_image)
>>> cbar_binary_image.set_ticks([0, 1])
>>> top.set_title("Binary image: foreground in white")

The middle image contains the distance transform using the ``taxicab``
metric.

>>> distance_taxicab = distance_transform_cdt(image, metric="taxicab")
>>> taxicab_transform = middle.imshow(distance_taxicab, cmap='gray')
>>> cbar_taxicab = middle.cax.colorbar(taxicab_transform)
>>> cbar_taxicab.set_ticks(colorbar_ticks)
>>> middle.set_title("Taxicab metric")

The bottom image contains the distance transform using the ``chessboard``
metric.

>>> distance_chessboard = distance_transform_cdt(image,
...                                              metric="chessboard")
>>> chessboard_transform = bottom.imshow(distance_chessboard, cmap='gray')
>>> cbar_chessboard = bottom.cax.colorbar(chessboard_transform)
>>> cbar_chessboard.set_ticks(colorbar_ticks)
>>> bottom.set_title("Chessboard metric")
>>> plt.tight_layout()
>>> plt.show()

r¡