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Use faster implementation of binary dilation using FFT #1638

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Oct 6, 2023
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Use faster implementation of binary dilation using FFT #1638

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9a56a6e
Faster implementation of binary dilation using FFT
larrybradley Oct 6, 2023
a44d899
Ensure footprint is bool array
larrybradley Oct 6, 2023
fcb54f5
Add changelog entry
larrybradley Oct 6, 2023
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5 changes: 5 additions & 0 deletions CHANGES.rst
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Expand Up @@ -9,6 +9,11 @@ General
New Features
^^^^^^^^^^^^

- ``photutils.segmentation``

- The ``SegmentationImage`` ``make_source_mask`` method now uses a
much faster implementation of binary dilation. [#1638]

Bug Fixes
^^^^^^^^^

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14 changes: 11 additions & 3 deletions photutils/segmentation/core.py
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Expand Up @@ -1147,7 +1147,8 @@ def make_source_mask(self, *, size=None, footprint=None):
return mask
else:
size = as_pair('size', size, check_odd=False)
footprint = np.ones(size)
footprint = np.ones(size, dtype=bool)
footprint = footprint.astype(bool)

if np.all(footprint):
# With a rectangular footprint, scipy grey_dilation is
Expand All @@ -1157,8 +1158,15 @@ def make_source_mask(self, *, size=None, footprint=None):
from scipy.ndimage import grey_dilation
return grey_dilation(mask, footprint=footprint)
else:
from scipy.ndimage import binary_dilation
return binary_dilation(mask, structure=footprint)
# Binary dilation is very slow, especially for large
# footprints. The following is a faster implementation
# using fast Fourier transforms (FFTs) that gives identical
# results to binary_dilation. Based on the following paper:
# "Dilation and Erosion of Gray Images with Spherical
# Masks", J. Kukal, D. Majerova, A. Prochazka (Jan 2007).
# https://www.researchgate.net/publication/238778666_DILATION_AND_EROSION_OF_GRAY_IMAGES_WITH_SPHERICAL_MASKS
from scipy.signal import fftconvolve
return fftconvolve(mask, footprint, 'same') > 0.5

@lazyproperty
def _geo_polygons(self):
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