prepro.py 文件源码

def elastic_transform(x, alpha, sigma, mode="constant", cval=0, is_random=False):
    """Elastic deformation of images as described in `[Simard2003] <http://deeplearning.cs.cmu.edu/pdfs/Simard.pdf>`_ .

    Parameters
    -----------
    x : numpy array, a greyscale image.
    alpha : scalar factor.
    sigma : scalar or sequence of scalars, the smaller the sigma, the more transformation.
        Standard deviation for Gaussian kernel. The standard deviations of the Gaussian filter are given for each axis as a sequence, or as a single number, in which case it is equal for all axes.
    mode : default constant, see `scipy.ndimage.filters.gaussian_filter <https://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.ndimage.filters.gaussian_filter.html>`_.
    cval : float, optional. Used in conjunction with mode ‘constant’, the value outside the image boundaries.
    is_random : boolean, default False

    Examples
    ---------
    >>> x = elastic_transform(x, alpha = x.shape[1] * 3, sigma = x.shape[1] * 0.07)

    References
    ------------
    - `Github <https://gist.github.com/chsasank/4d8f68caf01f041a6453e67fb30f8f5a>`_.
    - `Kaggle <https://www.kaggle.com/pscion/ultrasound-nerve-segmentation/elastic-transform-for-data-augmentation-0878921a>`_
    """
    if is_random is False:
        random_state = np.random.RandomState(None)
    else:
        random_state = np.random.RandomState(int(time.time()))
    #
    is_3d = False
    if len(x.shape) == 3 and x.shape[-1] == 1:
        x = x[:,:,0]
        is_3d = True
    elif len(x.shape) == 3 and x.shape[-1] != 1:
        raise Exception("Only support greyscale image")
    assert len(x.shape)==2

    shape = x.shape

    dx = gaussian_filter((random_state.rand(*shape) * 2 - 1), sigma, mode=mode, cval=cval) * alpha
    dy = gaussian_filter((random_state.rand(*shape) * 2 - 1), sigma, mode=mode, cval=cval) * alpha

    x_, y_ = np.meshgrid(np.arange(shape[0]), np.arange(shape[1]), indexing='ij')
    indices = np.reshape(x_ + dx, (-1, 1)), np.reshape(y_ + dy, (-1, 1))
    if is_3d:
        return map_coordinates(x, indices, order=1).reshape((shape[0], shape[1], 1))
    else:
        return map_coordinates(x, indices, order=1).reshape(shape)