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