mirror of
https://github.com/wassname/scikit-image.git
synced 2026-07-03 10:02:26 +08:00
Tony S Yu
122 lines
3.9 KiB
Cython
122 lines
3.9 KiB
Cython
"""template.py - Template matching
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"""
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import cython
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cimport numpy as np
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import numpy as np
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from scipy.signal import fftconvolve
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from skimage.transform import integral
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cdef extern from "math.h":
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float sqrt(float x)
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float fabs(float x)
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@cython.boundscheck(False)
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cdef float sum_integral(np.ndarray[float, ndim=2, mode="c"] sat,
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int r0, int c0, int r1, int c1):
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"""
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Using a summed area table / integral image, calculate the sum
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over a given window.
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This function is the same as the `integrate` function in
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`skimage.transform.integrate`, but this Cython version significantly
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speeds up the code.
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Parameters
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----------
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sat : ndarray of float
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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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cdef float 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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@cython.boundscheck(False)
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def match_template(np.ndarray[float, ndim=2, mode="c"] image,
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np.ndarray[float, ndim=2, mode="c"] template,
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str method):
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# convolve the image with template by frequency domain multiplication
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cdef np.ndarray[float, ndim=2] result
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# when `dtype=float` is used, ascontiguousarray returns ``double``.
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result = np.ascontiguousarray(fftconvolve(image, np.fliplr(template),
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mode="valid"), dtype=np.float32)
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# calculate squared integral images used for normalization
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cdef np.ndarray[float, ndim=2, mode="c"] integral_sum
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cdef np.ndarray[float, ndim=2, mode="c"] integral_sqr
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if method == 'norm-coeff':
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integral_sum = integral.integral_image(image)
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integral_sqr = integral.integral_image(image**2)
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# use inversed area for accuracy
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cdef float inv_area = 1.0 / (template.shape[0] * template.shape[1])
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cdef float template_norm
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cdef float template_mean = np.mean(template)
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if method == 'norm-corr':
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# calculate template norm according to the following:
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# variance = 1/K Sum[(x_k - mean) ** 2]
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# = 1/K Sum[x_k ** 2] - mean ** 2
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#template_norm = sqrt((np.std(template) ** 2 +
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#template_mean ** 2)) / sqrt(inv_area)
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# TODO: check equation for template_norm.
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# The above normalization factor is equivalent to the second-moment.
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template_norm = sqrt(np.sum(template**2))
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else:
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template_norm = sqrt((template_mean ** 2)) / sqrt(inv_area)
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# define window of template size in squared integral image
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cdef int i, j
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cdef float num, window_sum2, window_mean2, normed, t,
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# move window through convolution results, normalizing in the process
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for i in range(result.shape[0]):
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for j in range(result.shape[1]):
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num = result[i, j]
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i_end = i + template.shape[0]
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j_end = j + template.shape[1]
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window_mean2 = 0
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if method == 'norm-coeff':
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t = sum_integral(integral_sum, i, j, i_end, j_end)
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window_mean2 = t * t * inv_area
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num -= t*template_mean
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# calculate squared template window sum in the image
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window_sum2 = sum_integral(integral_sqr, i, j, i_end, j_end)
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normed = sqrt(window_sum2 - window_mean2) * template_norm
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# enforce some limits
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if fabs(num) < normed:
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num /= normed
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elif fabs(num) < normed*1.125:
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if num > 0:
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num = 1
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else:
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num = -1
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else:
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num = 0
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result[i, j] = num
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return result
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