elasticdeform

Deformation

elasticdeform.deform_random_grid(X, sigma=25, points=3, order=3, mode='constant', cval=0.0, crop=None, prefilter=True, axis=None, affine=None, rotate=None, zoom=None)[source]

Elastic deformation with a random deformation grid

This generates a random, square deformation grid with displacements sampled from from a normal distribution with standard deviation sigma. The deformation is then applied to the image or list of images,

See deform_grid for a full description of the parameters.

Parameters:

  • X (numpy array or list of arrays) – image, or list of images of the same size

  • sigma (float) – standard deviation of the normal distribution

  • points (array) – number of points of the deformation grid

  • rotate (float or None) – angle in degrees to rotate the output

    This only works for 2D images and rotates the image around the center of the output.

  • zoom (float or None) – scale factor to zoom the output

    This only works for 2D images and scales the image around the center of the output.

See also

deform_grid()
for a full description of the parameters.
elasticdeform.deform_grid(X, displacement, order=3, mode='constant', cval=0.0, crop=None, prefilter=True, axis=None, affine=None, rotate=None, zoom=None)[source]

Elastic deformation with a deformation grid

The procedure generates a coarse displacement grid with a random displacement for each grid point. This grid is then interpolated to compute a displacement for each pixel in the input image. The input image is then deformed using the displacement vectors and a spline interpolation.

Parameters:

  • X (numpy array or list of arrays) – image, or list of images of the same size

    If X is a list of images, the values for order, mode and cval can be lists to specify a different value for every image in X.

  • displacement (numpy array) – displacement vectors for each control point

    displacement is a NumPy array with displacement vectors for each control points. For example, to deform a 2D image with 3 x 5 control points, provide a displacement matrix of shape 2 x 3 x 5.

  • order ({0, 1, 2, 3, 4}) – interpolation order

  • mode (({nearest, wrap, reflect, mirror, constant})) – border mode

  • cval (float) – constant value to be used if mode == ‘constant’

  • crop (None or list) – None, or a list of slice() objects to crop the output

    crop can be a list of slice() objects to crop the output with. Only very simple slicing is supported: the slice start and stop values must be positive and should not be larger than the output. Note that this parameter is dependent of the axis parameter: if an axis list is given, crop must only contain slice() objects for the dimensions in axis.

  • prefilter (bool) – if True the input X will be pre-filtered with a spline filter

  • axis (None, int, a list of ints, or a list of lists of ints) – the axes to deform over

    axis indicates the axes on which the deformation should be applied. The default (None) is to apply a deformation to all dimensions of the input. Giving a single axis (int) or a tuple of axes will apply the deformation only to those axes. The shape of the displacement must match this number of axes. If multiple inputs are given, axis should be None or a list of tuples with the axes for each input.

  • affine (None, numpy array of shape (ndim, ndim + 1)) – affine transformation to apply to the output

    The affine transformation is applied to the output during interpolation.

  • rotate (float or None) – angle in degrees to rotate the output

    This only works for 2D images and rotates the image around the center of the output.

  • zoom (float or None) – scale factor to zoom the output

    This only works for 2D images and scales the image around the center of the output.
Returns:

The deformed image, or a list of deformed images if a list of inputs is given.
Return type:

numpy array or list of arrays

Notes

See the SciPy documentation for scipy.ndimage.interpolation.map_coordinates for more details on some of the parameters.

The elastic deformation approach is found in

Based on a Python implementation by Florian Calvet.

Gradient

elasticdeform.deform_grid_gradient(dY, displacement, order=3, mode='constant', cval=0.0, crop=None, prefilter=True, axis=None, X_shape=None, affine=None, rotate=None, zoom=None)[source]

Gradient for deform_grid.

This method performs the backward operation that returns the gradient of deform_grid with respect to the input. This is similar to performing an inverse deformation on the gradient, but not exactly the same: this function gives an exact gradient that also takes the interpolation into account.

The X_shape parameter specifices the shape of the original inputs, and is only necessary if the crop parameter is used. Otherwise, the input shape is the same as the shape of the gradient dY.

See the documentation for deform_grid.

Parameters:
  • dY (numpy array) – the input gradient, or list of gradients of the same size
  • displacement (numpy array) – displacement vectors for each control point
  • order ({0, 1, 2, 3, 4}) – interpolation order
  • mode (({nearest, wrap, reflect, mirror, constant})) – border mode
  • cval (float) – constant value to be used if mode == ‘constant’
  • crop (None or list) – None, or a list of slice() objects to crop the output
  • prefilter (bool) – if True the input X will be pre-filtered with a spline filter
  • axis (None, int, a list of ints, or a list of lists of ints) – the axes to deform over
  • X_shape (tuple with the shape of the input, or a list of tuples)
  • affine (None, numpy array of shape (ndim, ndim + 1)) – affine transformation to apply to the output
  • rotate (float or None) – angle in degrees to rotate the output
  • zoom (float or None) – scale factor to zoom the output
Returns:

Returns the gradient with respect to X.
Return type:

numpy array