mirror of
https://github.com/wassname/scikit-image.git
synced 2026-07-01 07:27:48 +08:00
Stefan van der Walt
61 lines
1.2 KiB
Python
61 lines
1.2 KiB
Python
def sat(x):
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"""Summed area table / integral image.
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The integral image contains the sum of all elements above and to the
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left of it, i.e.:
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.. math::
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S[m, n] = \sum_{i \leq m} \sum_{j \leq n} X[i, j]
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Parameters
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----------
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X : ndarray
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Input image.
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Returns
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-------
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S : ndarray
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Summed area table.
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References
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----------
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.. [1] F.C. Crow, "Summed-area tables for texture mapping,"
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ACM SIGGRAPH Computer Graphics, vol. 18, 1984, pp. 207-212.
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"""
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return x.cumsum(1).cumsum(0)
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def sat_sum(sat, r0, c0, r1, c1):
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"""Use a summed area table / integral image to sum over a given window.
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Parameters
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----------
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sat : ndarray
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Summed area table / integral image.
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r0, c0 : int
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Top-left corner of block to be summed.
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r1, c1 : int
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Bottom-right corner of block to be summed.
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Returns
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-------
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S : int
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Sum over the given window.
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"""
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S = 0
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S += sat[r1, c1]
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if (r0 - 1 >= 0) and (c0 - 1 >= 0):
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S += sat[r0 - 1, c0 - 1]
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if (r0 - 1 >= 0):
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S -= sat[r0 - 1, c1]
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if (c0 - 1 >= 0):
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S -= sat[r1, c0 - 1]
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return S
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