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# scipy.ndimage.filters.convolve

`scipy.ndimage.filters.``convolve`(input, weights, output=None, mode='reflect', cval=0.0, origin=0)

  Multi-dimensional convolution.

  The array is convolved with the given kernel.

  Parameters : | input : array_like Input array to filter. weights : array_like Array of weights, same number of dimensions as input output : ndarray, optional The output parameter passes an array in which to store the filter output. mode : {‘reflect’,’constant’,’nearest’,’mirror’, ‘wrap’}, optional the mode parameter determines how the array borders are handled. For ‘constant’ mode, values beyond borders are set to be cval. Default is ‘reflect’. cval : scalar, optional Value to fill past edges of input if mode is ‘constant’. Default is 0.0 origin : scalar, optional The origin parameter controls the placement of the filter. Default is 0.
  Returns : | result : ndarray The result of convolution of input with weights.

  See also

  `correlate`
    Correlate an image with a kernel.

  Notes

  Each value in result is , where W is the weights kernel, j is the n-D spatial index over , I is the input and k is the coordinate of the center of W, specified by origin in the input parameters.

  Examples

  Perhaps the simplest case to understand is `mode='constant', cval=0.0`, because in this case borders (i.e. where the weights kernel, centered on any one value, extends beyond an edge of input.

      >>> a = np.array([[1, 2, 0, 0],
      ....    [5, 3, 0, 4],
      ....    [0, 0, 0, 7],
      ....    [9, 3, 0, 0]])
      >>> b = np.array([[1,1,1],[1,1,0],[1,0,0]])
      >>> from scipy import ndimage
      >>> ndimage.convolve(a, k, mode='constant', cval=0.0)
      array([[11, 10,  7,  4],
             [10,  3, 11, 11],
             [15, 12, 14,  7],
             [12,  3,  7,  0]])

  Setting `cval=1.0` is equivalent to padding the outer edge of input with 1.0’s (and then extracting only the original region of the result).

      >>> ndimage.convolve(a, k, mode='constant', cval=1.0)
      array([[13, 11,  8,  7],
             [11,  3, 11, 14],
             [16, 12, 14, 10],
             [15,  6, 10,  5]])

  With `mode='reflect'` (the default), outer values are reflected at the edge of input to fill in missing values.

      >>> b = np.array([[2, 0, 0],
                        [1, 0, 0],
                        [0, 0, 0]])
      >>> k = np.array([[0,1,0],[0,1,0],[0,1,0]])
      array([[5, 0, 0],
             [3, 0, 0],
             [1, 0, 0]])

  This includes diagonally at the corners.

      >>> k = np.array([[1,0,0],[0,1,0],[0,0,1]])
      >>> ndimage.convolve(b, k)
      array([[4, 2, 0],
             [3, 2, 0],
             [1, 1, 0]])

  With `mode='nearest'`, the single nearest value in to an edge in input is repeated as many times as needed to match the overlapping weights.

      >>> c = np.array([[2, 0, 1],
                        [1, 0, 0],
                        [0, 0, 0]])
      >>> k = np.array([[0, 1, 0],
                        [0, 1, 0],
                        [0, 1, 0],
                        [0, 1, 0],
                        [0, 1, 0]])
      >>> ndimage.convolve(c, k, mode='nearest')
      array([[7, 0, 3],
             [5, 0, 2],
             [3, 0, 1]])

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