/usr/lib/python2.7/dist-packages/dipy/align/imaffine.py is in python-dipy 0.10.1-1.
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AffineMap: encapsulates the necessary information to perform affine
transforms between two domains, defined by a `static` and a `moving`
image. The `domain` of the transform is the set of points in the
`static` image's grid, and the `codomain` is the set of points in
the `moving` image. When we call the `transform` method, `AffineMap`
maps each point `x` of the domain (`static` grid) to the codomain
(`moving` grid) and interpolates the `moving` image at that point
to obtain the intensity value to be placed at `x` in the resulting
grid. The `transform_inverse` method performs the opposite operation
mapping points in the codomain to points in the domain.
ParzenJointHistogram: computes the marginal and joint distributions of
intensities of a pair of images, using Parzen windows [Parzen62]
with a cubic spline kernel, as proposed by Mattes et al. [Mattes03].
It also computes the gradient of the joint histogram w.r.t. the
parameters of a given transform.
MutualInformationMetric: computes the value and gradient of the mutual
information metric the way `Optimizer` needs them. That is, given
a set of transform parameters, it will use `ParzenJointHistogram`
to compute the value and gradient of the joint intensity histogram
evaluated at the given parameters, and evaluate the the value and
gradient of the histogram's mutual information.
AffineRegistration: it runs the multi-resolution registration, putting
all the pieces together. It needs to create the scale space of the
images and run the multi-resolution registration by using the Metric
and the Optimizer at each level of the Gaussian pyramid. At each
level, it will setup the metric to compute value and gradient of the
metric with the input images with different levels of smoothing.
References
----------
[Parzen62] E. Parzen. On the estimation of a probability density
function and the mode. Annals of Mathematical Statistics,
33(3), 1065-1076, 1962.
[Mattes03] Mattes, D., Haynor, D. R., Vesselle, H., Lewellen, T. K.,
& Eubank, W. PET-CT image registration in the chest using
free-form deformations. IEEE Transactions on Medical
Imaging, 22(1), 120-8, 2003.
"""
import numpy as np
import numpy.linalg as npl
import scipy.ndimage as ndimage
from ..core.optimize import Optimizer
from ..core.optimize import SCIPY_LESS_0_12
from . import vector_fields as vf
from . import VerbosityLevels
from .parzenhist import (ParzenJointHistogram,
sample_domain_regular,
compute_parzen_mi)
from .imwarp import (get_direction_and_spacings, ScaleSpace)
from .scalespace import IsotropicScaleSpace
from warnings import warn
_interp_options = ['nearest', 'linear']
_transform_method = {}
_transform_method[(2, 'nearest')] = vf.transform_2d_affine_nn
_transform_method[(3, 'nearest')] = vf.transform_3d_affine_nn
_transform_method[(2, 'linear')] = vf.transform_2d_affine
_transform_method[(3, 'linear')] = vf.transform_3d_affine
class AffineInversionError(Exception):
pass
class AffineMap(object):
def __init__(self, affine, domain_grid_shape=None, domain_grid2world=None,
codomain_grid_shape=None, codomain_grid2world=None):
""" AffineMap
Implements an affine transformation whose domain is given by
`domain_grid` and `domain_grid2world`, and whose co-domain is
given by `codomain_grid` and `codomain_grid2world`.
The actual transform is represented by the `affine` matrix, which
operate in world coordinates. Therefore, to transform a moving image
towards a static image, we first map each voxel (i,j,k) of the static
image to world coordinates (x,y,z) by applying `domain_grid2world`.
Then we apply the `affine` transform to (x,y,z) obtaining (x', y', z')
in moving image's world coordinates. Finally, (x', y', z') is mapped
to voxel coordinates (i', j', k') in the moving image by multiplying
(x', y', z') by the inverse of `codomain_grid2world`. The
`codomain_grid_shape` is used analogously to transform the static
image towards the moving image when calling `transform_inverse`.
If the domain/co-domain information is not provided (None) then the
sampling information needs to be specified each time the `transform`
or `transform_inverse` is called to transform images. Note that such
sampling information is not necessary to transform points defined in
physical space, such as stream lines.
Parameters
----------
affine : array, shape (dim + 1, dim + 1)
the matrix defining the affine transform, where `dim` is the
dimension of the space this map operates in (2 for 2D images,
3 for 3D images). If None, then `self` represents the identity
transformation.
domain_grid_shape : sequence, shape (dim,), optional
the shape of the default domain sampling grid. When `transform`
is called to transform an image, the resulting image will have
this shape, unless a different sampling information is provided.
If None, then the sampling grid shape must be specified each time
the `transform` method is called.
domain_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with the domain grid.
If None (the default), then the grid-to-world transform is assumed
to be the identity.
codomain_grid_shape : sequence of integers, shape (dim,)
the shape of the default co-domain sampling grid. When
`transform_inverse` is called to transform an image, the resulting
image will have this shape, unless a different sampling
information is provided. If None (the default), then the sampling
grid shape must be specified each time the `transform_inverse`
method is called.
codomain_grid2world : array, shape (dim + 1, dim + 1)
the grid-to-world transform associated with the co-domain grid.
If None (the default), then the grid-to-world transform is assumed
to be the identity.
"""
self.set_affine(affine)
self.domain_shape = domain_grid_shape
self.domain_grid2world = domain_grid2world
self.codomain_shape = codomain_grid_shape
self.codomain_grid2world = codomain_grid2world
def set_affine(self, affine):
""" Sets the affine transform (operating in physical space)
Also sets `self.affine_inv` - the inverse of `affine`, or None if
there is no inverse.
Parameters
----------
affine : array, shape (dim + 1, dim + 1)
the matrix representing the affine transform operating in
physical space. The domain and co-domain information
remains unchanged. If None, then `self` represents the identity
transformation.
"""
self.affine = affine
self.affine_inv = None
if self.affine is None:
return
if not np.all(np.isfinite(affine)):
raise AffineInversionError('Affine contains invalid elements')
try:
self.affine_inv = npl.inv(affine)
except npl.LinAlgError:
raise AffineInversionError('Affine cannot be inverted')
def _apply_transform(self, image, interp='linear', image_grid2world=None,
sampling_grid_shape=None, sampling_grid2world=None,
resample_only=False, apply_inverse=False):
""" Transforms the input image applying this affine transform
This is a generic function to transform images using either this
(direct) transform or its inverse.
If applying the direct transform (`apply_inverse=False`):
by default, the transformed image is sampled at a grid defined by
`self.domain_shape` and `self.domain_grid2world`.
If applying the inverse transform (`apply_inverse=True`):
by default, the transformed image is sampled at a grid defined by
`self.codomain_shape` and `self.codomain_grid2world`.
If the sampling information was not provided at initialization of this
transform then `sampling_grid_shape` is mandatory.
Parameters
----------
image : array, shape (X, Y) or (X, Y, Z)
the image to be transformed
interp : string, either 'linear' or 'nearest'
the type of interpolation to be used, either 'linear'
(for k-linear interpolation) or 'nearest' for nearest neighbor
image_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with `image`.
If None (the default), then the grid-to-world transform is assumed
to be the identity.
sampling_grid_shape : sequence, shape (dim,), optional
the shape of the grid where the transformed image must be sampled.
If None (the default), then `self.domain_shape` is used instead
(which must have been set at initialization, otherwise an exception
will be raised).
sampling_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with the sampling grid
(specified by `sampling_grid_shape`, or by default
`self.domain_shape`). If None (the default), then the
grid-to-world transform is assumed to be the identity.
resample_only : Boolean, optional
If False (the default) the affine transform is applied normally.
If True, then the affine transform is not applied, and the input
image is just re-sampled on the domain grid of this transform.
apply_inverse : Boolean, optional
If False (the default) the image is transformed from the codomain
of this transform to its domain using the (direct) affine
transform. Otherwise, the image is transformed from the domain
of this transform to its codomain using the (inverse) affine
transform.
Returns
-------
transformed : array, shape `sampling_grid_shape` or `self.domain_shape`
the transformed image, sampled at the requested grid
"""
# Verify valid interpolation requested
if interp not in _interp_options:
raise ValueError('Unknown interpolation method: %s' % (interp,))
# Obtain sampling grid
if sampling_grid_shape is None:
if apply_inverse:
sampling_grid_shape = self.codomain_shape
else:
sampling_grid_shape = self.domain_shape
if sampling_grid_shape is None:
msg = 'Unknown sampling info. Provide a valid sampling_grid_shape'
raise ValueError(msg)
dim = len(sampling_grid_shape)
shape = np.array(sampling_grid_shape, dtype=np.int32)
# Verify valid image dimension
img_dim = len(image.shape)
if img_dim < 2 or img_dim > 3:
raise ValueError('Undefined transform for dim: %d' % (img_dim,))
# Obtain grid-to-world transform for sampling grid
if sampling_grid2world is None:
if apply_inverse:
sampling_grid2world = self.codomain_grid2world
else:
sampling_grid2world = self.domain_grid2world
if sampling_grid2world is None:
sampling_grid2world = np.eye(dim + 1)
# Obtain world-to-grid transform for input image
if image_grid2world is None:
if apply_inverse:
image_grid2world = self.domain_grid2world
else:
image_grid2world = self.codomain_grid2world
if image_grid2world is None:
image_grid2world = np.eye(dim + 1)
image_world2grid = npl.inv(image_grid2world)
# Compute the transform from sampling grid to input image grid
if apply_inverse:
aff = self.affine_inv
else:
aff = self.affine
if (aff is None) or resample_only:
comp = image_world2grid.dot(sampling_grid2world)
else:
comp = image_world2grid.dot(aff.dot(sampling_grid2world))
# Transform the input image
if interp == 'linear':
image = image.astype(np.float64)
transformed = _transform_method[(dim, interp)](image, shape, comp)
return transformed
def transform(self, image, interp='linear', image_grid2world=None,
sampling_grid_shape=None, sampling_grid2world=None,
resample_only=False):
""" Transforms the input image from co-domain to domain space
By default, the transformed image is sampled at a grid defined by
`self.domain_shape` and `self.domain_grid2world`. If such
information was not provided then `sampling_grid_shape` is mandatory.
Parameters
----------
image : array, shape (X, Y) or (X, Y, Z)
the image to be transformed
interp : string, either 'linear' or 'nearest'
the type of interpolation to be used, either 'linear'
(for k-linear interpolation) or 'nearest' for nearest neighbor
image_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with `image`.
If None (the default), then the grid-to-world transform is assumed
to be the identity.
sampling_grid_shape : sequence, shape (dim,), optional
the shape of the grid where the transformed image must be sampled.
If None (the default), then `self.codomain_shape` is used instead
(which must have been set at initialization, otherwise an exception
will be raised).
sampling_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with the sampling grid
(specified by `sampling_grid_shape`, or by default
`self.codomain_shape`). If None (the default), then the
grid-to-world transform is assumed to be the identity.
resample_only : Boolean, optional
If False (the default) the affine transform is applied normally.
If True, then the affine transform is not applied, and the input
image is just re-sampled on the domain grid of this transform.
Returns
-------
transformed : array, shape `sampling_grid_shape` or
`self.codomain_shape`
the transformed image, sampled at the requested grid
"""
transformed = self._apply_transform(image, interp, image_grid2world,
sampling_grid_shape,
sampling_grid2world,
resample_only,
apply_inverse=False)
return np.array(transformed)
def transform_inverse(self, image, interp='linear', image_grid2world=None,
sampling_grid_shape=None, sampling_grid2world=None,
resample_only=False):
""" Transforms the input image from domain to co-domain space
By default, the transformed image is sampled at a grid defined by
`self.codomain_shape` and `self.codomain_grid2world`. If such
information was not provided then `sampling_grid_shape` is mandatory.
Parameters
----------
image : array, shape (X, Y) or (X, Y, Z)
the image to be transformed
interp : string, either 'linear' or 'nearest'
the type of interpolation to be used, either 'linear'
(for k-linear interpolation) or 'nearest' for nearest neighbor
image_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with `image`.
If None (the default), then the grid-to-world transform is assumed
to be the identity.
sampling_grid_shape : sequence, shape (dim,), optional
the shape of the grid where the transformed image must be sampled.
If None (the default), then `self.codomain_shape` is used instead
(which must have been set at initialization, otherwise an exception
will be raised).
sampling_grid2world : array, shape (dim + 1, dim + 1), optional
the grid-to-world transform associated with the sampling grid
(specified by `sampling_grid_shape`, or by default
`self.codomain_shape`). If None (the default), then the
grid-to-world transform is assumed to be the identity.
resample_only : Boolean, optional
If False (the default) the affine transform is applied normally.
If True, then the affine transform is not applied, and the input
image is just re-sampled on the domain grid of this transform.
Returns
-------
transformed : array, shape `sampling_grid_shape` or
`self.codomain_shape`
the transformed image, sampled at the requested grid
"""
transformed = self._apply_transform(image, interp, image_grid2world,
sampling_grid_shape,
sampling_grid2world,
resample_only,
apply_inverse=True)
return np.array(transformed)
class MutualInformationMetric(object):
def __init__(self, nbins=32, sampling_proportion=None):
r""" Initializes an instance of the Mutual Information metric
This class implements the methods required by Optimizer to drive the
registration process.
Parameters
----------
nbins : int, optional
the number of bins to be used for computing the intensity
histograms. The default is 32.
sampling_proportion : None or float in interval (0, 1], optional
There are two types of sampling: dense and sparse. Dense sampling
uses all voxels for estimating the (joint and marginal) intensity
histograms, while sparse sampling uses a subset of them. If
`sampling_proportion` is None, then dense sampling is
used. If `sampling_proportion` is a floating point value in (0,1]
then sparse sampling is used, where `sampling_proportion`
specifies the proportion of voxels to be used. The default is
None.
Notes
-----
Since we use linear interpolation, images are not, in general,
differentiable at exact voxel coordinates, but they are differentiable
between voxel coordinates. When using sparse sampling, selected voxels
are slightly moved by adding a small random displacement within one
voxel to prevent sampling points from being located exactly at voxel
coordinates. When using dense sampling, this random displacement is
not applied.
"""
self.histogram = ParzenJointHistogram(nbins)
self.sampling_proportion = sampling_proportion
self.metric_val = None
self.metric_grad = None
def setup(self, transform, static, moving, static_grid2world=None,
moving_grid2world=None, starting_affine=None):
r""" Prepares the metric to compute intensity densities and gradients
The histograms will be setup to compute probability densities of
intensities within the minimum and maximum values of `static` and
`moving`
Parameters
----------
transform: instance of Transform
the transformation with respect to whose parameters the gradient
must be computed
static : array, shape (S, R, C) or (R, C)
static image
moving : array, shape (S', R', C') or (R', C')
moving image. The dimensions of the static (S, R, C) and moving
(S', R', C') images do not need to be the same.
static_grid2world : array (dim+1, dim+1), optional
the grid-to-space transform of the static image. The default is
None, implying the transform is the identity.
moving_grid2world : array (dim+1, dim+1)
the grid-to-space transform of the moving image. The default is
None, implying the spacing along all axes is 1.
starting_affine : array, shape (dim+1, dim+1), optional
the pre-aligning matrix (an affine transform) that roughly aligns
the moving image towards the static image. If None, no
pre-alignment is performed. If a pre-alignment matrix is available,
it is recommended to provide this matrix as `starting_affine`
instead of manually transforming the moving image to reduce
interpolation artifacts. The default is None, implying no
pre-alignment is performed.
"""
n = transform.get_number_of_parameters()
self.metric_grad = np.zeros(n, dtype=np.float64)
self.dim = len(static.shape)
if moving_grid2world is None:
moving_grid2world = np.eye(self.dim + 1)
if static_grid2world is None:
static_grid2world = np.eye(self.dim + 1)
self.transform = transform
self.static = np.array(static).astype(np.float64)
self.moving = np.array(moving).astype(np.float64)
self.static_grid2world = static_grid2world
self.static_world2grid = npl.inv(static_grid2world)
self.moving_grid2world = moving_grid2world
self.moving_world2grid = npl.inv(moving_grid2world)
self.static_direction, self.static_spacing = \
get_direction_and_spacings(static_grid2world, self.dim)
self.moving_direction, self.moving_spacing = \
get_direction_and_spacings(moving_grid2world, self.dim)
self.starting_affine = starting_affine
P = np.eye(self.dim + 1)
if self.starting_affine is not None:
P = self.starting_affine
self.affine_map = AffineMap(P, static.shape, static_grid2world,
moving.shape, moving_grid2world)
if self.dim == 2:
self.interp_method = vf.interpolate_scalar_2d
else:
self.interp_method = vf.interpolate_scalar_3d
if self.sampling_proportion is None:
self.samples = None
self.ns = 0
else:
k = int(np.ceil(1.0 / self.sampling_proportion))
shape = np.array(static.shape, dtype=np.int32)
self.samples = sample_domain_regular(k, shape, static_grid2world)
self.samples = np.array(self.samples)
self.ns = self.samples.shape[0]
# Add a column of ones (homogeneous coordinates)
self.samples = np.hstack((self.samples, np.ones(self.ns)[:, None]))
if self.starting_affine is None:
self.samples_prealigned = self.samples
else:
self.samples_prealigned =\
self.starting_affine.dot(self.samples.T).T
# Sample the static image
static_p = self.static_world2grid.dot(self.samples.T).T
static_p = static_p[..., :self.dim]
self.static_vals, inside = self.interp_method(static, static_p)
self.static_vals = np.array(self.static_vals, dtype=np.float64)
self.histogram.setup(self.static, self.moving)
def _update_histogram(self):
r""" Updates the histogram according to the current affine transform
The current affine transform is given by `self.affine_map`, which
must be set before calling this method.
Returns
-------
static_values: array, shape(n,) if sparse sampling is being used,
array, shape(S, R, C) or (R, C) if dense sampling
the intensity values corresponding to the static image used to
update the histogram. If sparse sampling is being used, then
it is simply a sequence of scalars, obtained by sampling the static
image at the `n` sampling points. If dense sampling is being used,
then the intensities are given directly by the static image,
whose shape is (S, R, C) in the 3D case or (R, C) in the 2D case.
moving_values: array, shape(n,) if sparse sampling is being used,
array, shape(S, R, C) or (R, C) if dense sampling
the intensity values corresponding to the moving image used to
update the histogram. If sparse sampling is being used, then
it is simply a sequence of scalars, obtained by sampling the moving
image at the `n` sampling points (mapped to the moving space by the
current affine transform). If dense sampling is being used,
then the intensities are given by the moving imaged linearly
transformed towards the static image by the current affine, which
results in an image of the same shape as the static image.
"""
static_values = None
moving_values = None
if self.sampling_proportion is None: # Dense case
static_values = self.static
moving_values = self.affine_map.transform(self.moving)
self.histogram.update_pdfs_dense(static_values, moving_values)
else: # Sparse case
sp_to_moving = self.moving_world2grid.dot(self.affine_map.affine)
pts = sp_to_moving.dot(self.samples.T).T # Points on moving grid
pts = pts[..., :self.dim]
self.moving_vals, inside = self.interp_method(self.moving, pts)
self.moving_vals = np.array(self.moving_vals)
static_values = self.static_vals
moving_values = self.moving_vals
self.histogram.update_pdfs_sparse(static_values, moving_values)
return static_values, moving_values
def _update_mutual_information(self, params, update_gradient=True):
r""" Updates marginal and joint distributions and the joint gradient
The distributions are updated according to the static and transformed
images. The transformed image is precisely the moving image after
transforming it by the transform defined by the `params` parameters.
The gradient of the joint PDF is computed only if update_gradient
is True.
Parameters
----------
params : array, shape (n,)
the parameter vector of the transform currently used by the metric
(the transform name is provided when self.setup is called), n is
the number of parameters of the transform
update_gradient : Boolean, optional
if True, the gradient of the joint PDF will also be computed,
otherwise, only the marginal and joint PDFs will be computed.
The default is True.
"""
# Get the matrix associated with the `params` parameter vector
current_affine = self.transform.param_to_matrix(params)
# Get the static-to-prealigned matrix (only needed for the MI gradient)
static2prealigned = self.static_grid2world
if self.starting_affine is not None:
current_affine = current_affine.dot(self.starting_affine)
static2prealigned = self.starting_affine.dot(static2prealigned)
self.affine_map.set_affine(current_affine)
# Update the histogram with the current joint intensities
static_values, moving_values = self._update_histogram()
H = self.histogram # Shortcut to `self.histogram`
grad = None # Buffer to write the MI gradient into (if needed)
if update_gradient:
grad = self.metric_grad
# Compute the gradient of the joint PDF w.r.t. parameters
if self.sampling_proportion is None: # Dense case
# Compute the gradient of moving img. at physical points
# associated with the >>static image's grid<< cells
# The image gradient must be eval. at current moved points
grid_to_world = current_affine.dot(self.static_grid2world)
mgrad, inside = vf.gradient(self.moving,
self.moving_world2grid,
self.moving_spacing,
self.static.shape,
grid_to_world)
# The Jacobian must be evaluated at the pre-aligned points
H.update_gradient_dense(params, self.transform, static_values,
moving_values, static2prealigned, mgrad)
else: # Sparse case
# Compute the gradient of moving at the sampling points
# which are already given in physical space coordinates
pts = current_affine.dot(self.samples.T).T # Moved points
mgrad, inside = vf.sparse_gradient(self.moving,
self.moving_world2grid,
self.moving_spacing,
pts)
# The Jacobian must be evaluated at the pre-aligned points
pts = self.samples_prealigned[..., :self.dim]
H.update_gradient_sparse(params, self.transform, static_values,
moving_values, pts, mgrad)
# Call the cythonized MI computation with self.histogram fields
self.metric_val = compute_parzen_mi(H.joint, H.joint_grad,
H.smarginal, H.mmarginal,
grad)
def distance(self, params):
r""" Numeric value of the negative Mutual Information
We need to change the sign so we can use standard minimization
algorithms.
Parameters
----------
params : array, shape (n,)
the parameter vector of the transform currently used by the metric
(the transform name is provided when self.setup is called), n is
the number of parameters of the transform
Returns
-------
neg_mi : float
the negative mutual information of the input images after
transforming the moving image by the currently set transform
with `params` parameters
"""
try:
self._update_mutual_information(params, False)
except AffineInversionError:
return np.inf
return -1 * self.metric_val
def gradient(self, params):
r""" Numeric value of the metric's gradient at the given parameters
Parameters
----------
params : array, shape (n,)
the parameter vector of the transform currently used by the metric
(the transform name is provided when self.setup is called), n is
the number of parameters of the transform
Returns
-------
grad : array, shape (n,)
the gradient of the negative Mutual Information
"""
try:
self._update_mutual_information(params, True)
except AffineInversionError:
return 0 * self.metric_grad
return -1 * self.metric_grad
def distance_and_gradient(self, params):
r""" Numeric value of the metric and its gradient at given parameters
Parameters
----------
params : array, shape (n,)
the parameter vector of the transform currently used by the metric
(the transform name is provided when self.setup is called), n is
the number of parameters of the transform
Returns
-------
neg_mi : float
the negative mutual information of the input images after
transforming the moving image by the currently set transform
with `params` parameters
neg_mi_grad : array, shape (n,)
the gradient of the negative Mutual Information
"""
try:
self._update_mutual_information(params, True)
except AffineInversionError:
return np.inf, 0 * self.metric_grad
return -1 * self.metric_val, -1 * self.metric_grad
class AffineRegistration(object):
def __init__(self,
metric=None,
level_iters=None,
sigmas=None,
factors=None,
method='L-BFGS-B',
ss_sigma_factor=None,
options=None):
r""" Initializes an instance of the AffineRegistration class
Parameters
----------
metric : None or object, optional
an instance of a metric. The default is None, implying
the Mutual Information metric with default settings.
level_iters : sequence, optional
the number of iterations at each scale of the scale space.
`level_iters[0]` corresponds to the coarsest scale,
`level_iters[-1]` the finest, where n is the length of the
sequence. By default, a 3-level scale space with iterations
sequence equal to [10000, 1000, 100] will be used.
sigmas : sequence of floats, optional
custom smoothing parameter to build the scale space (one parameter
for each scale). By default, the sequence of sigmas will be
[3, 1, 0].
factors : sequence of floats, optional
custom scale factors to build the scale space (one factor for each
scale). By default, the sequence of factors will be [4, 2, 1].
method : string, optional
optimization method to be used. If Scipy version < 0.12, then
only L-BFGS-B is available. Otherwise, `method` can be any
gradient-based method available in `dipy.core.Optimize`: CG, BFGS,
Newton-CG, dogleg or trust-ncg.
The default is 'L-BFGS-B'.
ss_sigma_factor : float, optional
If None, this parameter is not used and an isotropic scale
space with the given `factors` and `sigmas` will be built.
If not None, an anisotropic scale space will be used by
automatically selecting the smoothing sigmas along each axis
according to the voxel dimensions of the given image.
The `ss_sigma_factor` is used to scale the automatically computed
sigmas. For example, in the isotropic case, the sigma of the
kernel will be $factor * (2 ^ i)$ where
$i = 1, 2, ..., n_scales - 1$ is the scale (the finest resolution
image $i=0$ is never smoothed). The default is None.
options : dict, optional
extra optimization options. The default is None, implying
no extra options are passed to the optimizer.
"""
self.metric = metric
if self.metric is None:
self.metric = MutualInformationMetric()
if level_iters is None:
level_iters = [10000, 1000, 100]
self.level_iters = level_iters
self.levels = len(level_iters)
if self.levels == 0:
raise ValueError('The iterations sequence cannot be empty')
self.options = options
self.method = method
if ss_sigma_factor is not None:
self.use_isotropic = False
self.ss_sigma_factor = ss_sigma_factor
else:
self.use_isotropic = True
if factors is None:
factors = [4, 2, 1]
if sigmas is None:
sigmas = [3, 1, 0]
self.factors = factors
self.sigmas = sigmas
self.verbosity = VerbosityLevels.STATUS
def _init_optimizer(self, static, moving, transform, params0,
static_grid2world, moving_grid2world,
starting_affine):
r"""Initializes the registration optimizer
Initializes the optimizer by computing the scale space of the input
images
Parameters
----------
static : array, shape (S, R, C) or (R, C)
the image to be used as reference during optimization.
moving : array, shape (S', R', C') or (R', C')
the image to be used as "moving" during optimization. The
dimensions of the static (S, R, C) and moving (S', R', C') images
do not need to be the same.
transform : instance of Transform
the transformation with respect to whose parameters the gradient
must be computed
params0 : array, shape (n,)
parameters from which to start the optimization. If None, the
optimization will start at the identity transform. n is the
number of parameters of the specified transformation.
static_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation associated with the static image
moving_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation associated with the moving image
starting_affine : string, or matrix, or None
If string:
'mass': align centers of gravity
'voxel-origin': align physical coordinates of voxel (0,0,0)
'centers': align physical coordinates of central voxels
If matrix:
array, shape (dim+1, dim+1)
If None:
Start from identity
"""
self.dim = len(static.shape)
self.transform = transform
n = transform.get_number_of_parameters()
self.nparams = n
if params0 is None:
params0 = self.transform.get_identity_parameters()
self.params0 = params0
if starting_affine is None:
self.starting_affine = np.eye(self.dim + 1)
elif isinstance(starting_affine, str):
if starting_affine == 'mass':
affine_map = transform_centers_of_mass(static,
static_grid2world,
moving,
moving_grid2world)
self.starting_affine = affine_map.affine
elif starting_affine == 'voxel-origin':
affine_map = transform_origins(static, static_grid2world,
moving, moving_grid2world)
self.starting_affine = affine_map.affine
elif starting_affine == 'centers':
affine_map = transform_geometric_centers(static,
static_grid2world,
moving,
moving_grid2world)
self.starting_affine = affine_map.affine
else:
raise ValueError('Invalid starting_affine strategy')
elif (isinstance(starting_affine, np.ndarray) and
starting_affine.shape >= (self.dim, self.dim + 1)):
self.starting_affine = starting_affine
else:
raise ValueError('Invalid starting_affine matrix')
# Extract information from affine matrices to create the scale space
static_direction, static_spacing = \
get_direction_and_spacings(static_grid2world, self.dim)
moving_direction, moving_spacing = \
get_direction_and_spacings(moving_grid2world, self.dim)
static = ((static.astype(np.float64) - static.min()) /
(static.max() - static.min()))
moving = ((moving.astype(np.float64) - moving.min()) /
(moving.max() - moving.min()))
# Build the scale space of the input images
if self.use_isotropic:
self.moving_ss = IsotropicScaleSpace(moving, self.factors,
self.sigmas,
moving_grid2world,
moving_spacing, False)
self.static_ss = IsotropicScaleSpace(static, self.factors,
self.sigmas,
static_grid2world,
static_spacing, False)
else:
self.moving_ss = ScaleSpace(moving, self.levels, moving_grid2world,
moving_spacing, self.ss_sigma_factor,
False)
self.static_ss = ScaleSpace(static, self.levels, static_grid2world,
static_spacing, self.ss_sigma_factor,
False)
def optimize(self, static, moving, transform, params0,
static_grid2world=None, moving_grid2world=None,
starting_affine=None):
r''' Starts the optimization process
Parameters
----------
static : array, shape (S, R, C) or (R, C)
the image to be used as reference during optimization.
moving : array, shape (S', R', C') or (R', C')
the image to be used as "moving" during optimization. It is
necessary to pre-align the moving image to ensure its domain
lies inside the domain of the deformation fields. This is assumed
to be accomplished by "pre-aligning" the moving image towards the
static using an affine transformation given by the
'starting_affine' matrix
transform : instance of Transform
the transformation with respect to whose parameters the gradient
must be computed
params0 : array, shape (n,)
parameters from which to start the optimization. If None, the
optimization will start at the identity transform. n is the
number of parameters of the specified transformation.
static_grid2world : array, shape (dim+1, dim+1), optional
the voxel-to-space transformation associated with the static
image. The default is None, implying the transform is the
identity.
moving_grid2world : array, shape (dim+1, dim+1), optional
the voxel-to-space transformation associated with the moving
image. The default is None, implying the transform is the
identity.
starting_affine : string, or matrix, or None, optional
If string:
'mass': align centers of gravity
'voxel-origin': align physical coordinates of voxel (0,0,0)
'centers': align physical coordinates of central voxels
If matrix:
array, shape (dim+1, dim+1).
If None:
Start from identity.
The default is None.
Returns
-------
affine_map : instance of AffineMap
the affine resulting affine transformation
'''
self._init_optimizer(static, moving, transform, params0,
static_grid2world, moving_grid2world,
starting_affine)
del starting_affine # Now we must refer to self.starting_affine
# Multi-resolution iterations
original_static_shape = self.static_ss.get_image(0).shape
original_static_grid2world = self.static_ss.get_affine(0)
original_moving_shape = self.moving_ss.get_image(0).shape
original_moving_grid2world = self.moving_ss.get_affine(0)
affine_map = AffineMap(None,
original_static_shape,
original_static_grid2world,
original_moving_shape,
original_moving_grid2world)
for level in range(self.levels - 1, -1, -1):
self.current_level = level
max_iter = self.level_iters[-1 - level]
if self.verbosity >= VerbosityLevels.STATUS:
print('Optimizing level %d [max iter: %d]' % (level, max_iter))
# Resample the smooth static image to the shape of this level
smooth_static = self.static_ss.get_image(level)
current_static_shape = self.static_ss.get_domain_shape(level)
current_static_grid2world = self.static_ss.get_affine(level)
current_affine_map = AffineMap(None,
current_static_shape,
current_static_grid2world,
original_static_shape,
original_static_grid2world)
current_static = current_affine_map.transform(smooth_static)
# The moving image is full resolution
current_moving_grid2world = original_moving_grid2world
current_moving = self.moving_ss.get_image(level)
# Prepare the metric for iterations at this resolution
self.metric.setup(transform, current_static, current_moving,
current_static_grid2world,
current_moving_grid2world, self.starting_affine)
# Optimize this level
if self.options is None:
self.options = {'gtol': 1e-4,
'disp': False}
if self.method == 'L-BFGS-B':
self.options['maxfun'] = max_iter
else:
self.options['maxiter'] = max_iter
if SCIPY_LESS_0_12:
# Older versions don't expect value and gradient from
# the same function
opt = Optimizer(self.metric.distance, self.params0,
method=self.method, jac=self.metric.gradient,
options=self.options)
else:
opt = Optimizer(self.metric.distance_and_gradient, self.params0,
method=self.method, jac=True,
options=self.options)
params = opt.xopt
# Update starting_affine matrix with optimal parameters
T = self.transform.param_to_matrix(params)
self.starting_affine = T.dot(self.starting_affine)
# Start next iteration at identity
self.params0 = self.transform.get_identity_parameters()
affine_map.set_affine(self.starting_affine)
return affine_map
def align_centers_of_mass(static, static_grid2world,
moving, moving_grid2world):
msg = "This function is deprecated please use"
msg += " dipy.align.imaffine.transform_centers_of_mass instead."
warn(msg)
return transform_centers_of_mass(static, static_grid2world,
moving, moving_grid2world)
def align_geometric_centers(static, static_grid2world,
moving, moving_grid2world):
msg = "This function is deprecated please use"
msg += " dipy.align.imaffine.transform_geometric_centers instead."
warn(msg)
return transform_geometric_centers(static, static_grid2world,
moving, moving_grid2world)
def align_origins(static, static_grid2world,
moving, moving_grid2world):
msg = "This function is deprecated please use"
msg += " dipy.align.imaffine.transform_origins instead."
warn(msg)
return transform_origins(static, static_grid2world,
moving, moving_grid2world)
def transform_centers_of_mass(static, static_grid2world,
moving, moving_grid2world):
r""" Transformation to align the center of mass of the input images
Parameters
----------
static : array, shape (S, R, C)
static image
static_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation of the static image
moving : array, shape (S, R, C)
moving image
moving_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation of the moving image
Returns
-------
affine_map : instance of AffineMap
the affine transformation (translation only, in this case) aligning
the center of mass of the moving image towards the one of the static
image
"""
dim = len(static.shape)
if static_grid2world is None:
static_grid2world = np.eye(dim + 1)
if moving_grid2world is None:
moving_grid2world = np.eye(dim + 1)
c_static = ndimage.measurements.center_of_mass(np.array(static))
c_static = static_grid2world.dot(c_static+(1,))
c_moving = ndimage.measurements.center_of_mass(np.array(moving))
c_moving = moving_grid2world.dot(c_moving+(1,))
transform = np.eye(dim + 1)
transform[:dim, dim] = (c_moving - c_static)[:dim]
affine_map = AffineMap(transform,
static.shape, static_grid2world,
moving.shape, moving_grid2world)
return affine_map
def transform_geometric_centers(static, static_grid2world,
moving, moving_grid2world):
r""" Transformation to align the geometric center of the input images
With "geometric center" of a volume we mean the physical coordinates of
its central voxel
Parameters
----------
static : array, shape (S, R, C)
static image
static_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation of the static image
moving : array, shape (S, R, C)
moving image
moving_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation of the moving image
Returns
-------
affine_map : instance of AffineMap
the affine transformation (translation only, in this case) aligning
the geometric center of the moving image towards the one of the static
image
"""
dim = len(static.shape)
if static_grid2world is None:
static_grid2world = np.eye(dim + 1)
if moving_grid2world is None:
moving_grid2world = np.eye(dim + 1)
c_static = tuple((np.array(static.shape, dtype=np.float64)) * 0.5)
c_static = static_grid2world.dot(c_static+(1,))
c_moving = tuple((np.array(moving.shape, dtype=np.float64)) * 0.5)
c_moving = moving_grid2world.dot(c_moving+(1,))
transform = np.eye(dim + 1)
transform[:dim, dim] = (c_moving - c_static)[:dim]
affine_map = AffineMap(transform,
static.shape, static_grid2world,
moving.shape, moving_grid2world)
return affine_map
def transform_origins(static, static_grid2world,
moving, moving_grid2world):
r""" Transformation to align the origins of the input images
With "origin" of a volume we mean the physical coordinates of
voxel (0,0,0)
Parameters
----------
static : array, shape (S, R, C)
static image
static_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation of the static image
moving : array, shape (S, R, C)
moving image
moving_grid2world : array, shape (dim+1, dim+1)
the voxel-to-space transformation of the moving image
Returns
-------
affine_map : instance of AffineMap
the affine transformation (translation only, in this case) aligning
the origin of the moving image towards the one of the static
image
"""
dim = len(static.shape)
if static_grid2world is None:
static_grid2world = np.eye(dim + 1)
if moving_grid2world is None:
moving_grid2world = np.eye(dim + 1)
c_static = static_grid2world[:dim, dim]
c_moving = moving_grid2world[:dim, dim]
transform = np.eye(dim + 1)
transform[:dim, dim] = (c_moving - c_static)[:dim]
affine_map = AffineMap(transform,
static.shape, static_grid2world,
moving.shape, moving_grid2world)
return affine_map
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