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Nelle Varoquaux
61 lines
1.2 KiB
Python
61 lines
1.2 KiB
Python
def integral_image(x):
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"""Integral image / summed area table.
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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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Integral image / 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 integrate(ii, r0, c0, r1, c1):
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"""Use an integral image to integrate over a given window.
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Parameters
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----------
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ii : ndarray
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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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Integral (sum) over the given window.
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"""
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S = 0
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S += ii[r1, c1]
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if (r0 - 1 >= 0) and (c0 - 1 >= 0):
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S += ii[r0 - 1, c0 - 1]
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if (r0 - 1 >= 0):
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S -= ii[r0 - 1, c1]
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if (c0 - 1 >= 0):
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S -= ii[r1, c0 - 1]
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return S
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