import numpy as np
from . import draw
[文档]
def polygon2mask(image_shape, polygon):
"""Create a binary mask from a polygon.
Parameters
----------
image_shape : tuple of size 2
The shape of the mask.
polygon : (N, 2) array_like
The polygon coordinates of shape (N, 2) where N is
the number of points. The coordinates are (row, column).
Returns
-------
mask : 2-D ndarray of type 'bool'
The binary mask that corresponds to the input polygon.
See Also
--------
polygon:
Generate coordinates of pixels inside a polygon.
Notes
-----
This function does not do any border checking. Parts of the polygon that
are outside the coordinate space defined by `image_shape` are not drawn.
Examples
--------
>>> import skimage as ski
>>> image_shape = (10, 10)
>>> polygon = np.array([[1, 1], [2, 7], [8, 4]])
>>> mask = ski.draw.polygon2mask(image_shape, polygon)
>>> mask.astype(int)
array([[0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 1, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 1, 1, 1, 1, 1, 1, 0, 0],
[0, 0, 1, 1, 1, 1, 1, 0, 0, 0],
[0, 0, 0, 1, 1, 1, 1, 0, 0, 0],
[0, 0, 0, 1, 1, 1, 0, 0, 0, 0],
[0, 0, 0, 0, 1, 1, 0, 0, 0, 0],
[0, 0, 0, 0, 1, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 1, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]])
If vertices / points of the `polygon` are outside the coordinate space
defined by `image_shape`, only a part (or none at all) of the polygon is
drawn in the mask.
>>> offset = np.array([[2, -4]])
>>> ski.draw.polygon2mask(image_shape, polygon - offset).astype(int)
array([[0, 0, 0, 0, 0, 0, 1, 1, 1, 1],
[0, 0, 0, 0, 0, 0, 1, 1, 1, 1],
[0, 0, 0, 0, 0, 0, 0, 1, 1, 1],
[0, 0, 0, 0, 0, 0, 0, 1, 1, 1],
[0, 0, 0, 0, 0, 0, 0, 0, 1, 1],
[0, 0, 0, 0, 0, 0, 0, 0, 1, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 1, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]])
"""
polygon = np.asarray(polygon)
vertex_row_coords, vertex_col_coords = polygon.T
fill_row_coords, fill_col_coords = draw.polygon(
vertex_row_coords, vertex_col_coords, image_shape
)
mask = np.zeros(image_shape, dtype=bool)
mask[fill_row_coords, fill_col_coords] = True
return mask
