# -*- coding: utf-8 -*-
from __future__ import absolute_import, print_function
import warnings
import numpy as np
import scipy.ndimage as ndi
from niftynet.layer.base_layer import RandomisedLayer
warnings.simplefilter("ignore", UserWarning)
warnings.simplefilter("ignore", RuntimeWarning)
[docs]class RandomSpatialScalingLayer(RandomisedLayer):
"""
generate randomised scaling along each dim for data augmentation
"""
def __init__(self,
min_percentage=-10.0,
max_percentage=10.0,
antialiasing=True,
isotropic=False,
name='random_spatial_scaling'):
super(RandomSpatialScalingLayer, self).__init__(name=name)
assert min_percentage <= max_percentage
self._min_percentage = max(min_percentage, -99.9)
self._max_percentage = max_percentage
self.antialiasing = antialiasing
self.isotropic = isotropic
self._rand_zoom = None
[docs] def randomise(self, spatial_rank=3):
spatial_rank = int(np.floor(spatial_rank))
if self.isotropic:
one_rand_zoom = np.random.uniform(low=self._min_percentage,
high=self._max_percentage)
rand_zoom = np.repeat(one_rand_zoom, spatial_rank)
else:
rand_zoom = np.random.uniform(low=self._min_percentage,
high=self._max_percentage,
size=(spatial_rank,))
self._rand_zoom = (rand_zoom + 100.0) / 100.0
def _get_sigma(self, zoom):
"""
Compute optimal standard deviation for Gaussian kernel.
Cardoso et al., "Scale factor point spread function matching:
beyond aliasing in image resampling", MICCAI 2015
"""
k = 1 / zoom
variance = (k ** 2 - 1 ** 2) * (2 * np.sqrt(2 * np.log(2))) ** (-2)
sigma = np.sqrt(variance)
return sigma
def _apply_transformation(self, image, interp_order=3):
if interp_order < 0:
return image
assert self._rand_zoom is not None
full_zoom = np.array(self._rand_zoom)
while len(full_zoom) < image.ndim:
full_zoom = np.hstack((full_zoom, [1.0]))
is_undersampling = all(full_zoom[:3] < 1)
run_antialiasing_filter = self.antialiasing and is_undersampling
if run_antialiasing_filter:
sigma = self._get_sigma(full_zoom[:3])
if image.ndim == 4:
output = []
for mod in range(image.shape[-1]):
to_scale = ndi.gaussian_filter(image[..., mod], sigma) if \
run_antialiasing_filter else image[..., mod]
scaled = ndi.zoom(to_scale, full_zoom[:3], order=interp_order)
output.append(scaled[..., np.newaxis])
return np.concatenate(output, axis=-1)
elif image.ndim == 3:
to_scale = ndi.gaussian_filter(image, sigma) \
if run_antialiasing_filter else image
scaled = ndi.zoom(
to_scale, full_zoom[:3], order=interp_order)
return scaled[..., np.newaxis]
else:
raise NotImplementedError('not implemented random scaling')
[docs] def layer_op(self, inputs, interp_orders, *args, **kwargs):
if inputs is None:
return inputs
if isinstance(inputs, dict) and isinstance(interp_orders, dict):
for (field, image) in inputs.items():
transformed_data = []
interp_order = interp_orders[field][0]
for mod_i in range(image.shape[-1]):
scaled_data = self._apply_transformation(
image[..., mod_i], interp_order)
transformed_data.append(scaled_data[..., np.newaxis])
inputs[field] = np.concatenate(transformed_data, axis=-1)
# shapes = []
# for (field, image) in inputs.items():
# shapes.append(image.shape)
# assert(len(shapes) == 2 and shapes[0][0:4] == shapes[1][0:4]), shapes
else:
raise NotImplementedError("unknown input format")
return inputs
