108-resize (#125)

* Add Resize transform (spatial scaling).

* Adding tests.

monai/transforms/transforms.py

@@ -15,6 +15,7 @@
 
 import numpy as np
 import torch
+from skimage.transform import resize
 import scipy.ndimage
 
 import monai
@@ -81,6 +82,47 @@ def __call__(self, img):
         return np.flip(img, self.axis)
 
 
+@export
+class Resize:
+    """
+    Resize the input image to given resolution. Uses skimage.transform.resize underneath.
+    For additional details, see https://scikit-image.org/docs/dev/api/skimage.transform.html#skimage.transform.resize.
+
+    Args:
+        order (int): Order of spline interpolation. Default=1.
+        mode (str): Points outside boundaries are filled according to given mode. 
+            Options are 'constant', 'edge', 'symmetric', 'reflect', 'wrap'.
+        cval (float): Used with mode 'constant', the value outside image boundaries.
+        clip (bool): Wheter to clip range of output values after interpolation. Default: True.
+        preserve_range (bool): Whether to keep original range of values. Default is True.
+            If False, input is converted according to conventions of img_as_float. See 
+            https://scikit-image.org/docs/dev/user_guide/data_types.html.
+        anti_aliasing (bool): Whether to apply a gaussian filter to image before down-scaling.
+            Default is True.
+        anti_aliasing_sigma (float, tuple of floats): Standard deviation for gaussian filtering.
+    """
+
+    def __init__(self, output_shape, order=1, mode='reflect', cval=0,
+                 clip=True, preserve_range=True, 
+                 anti_aliasing=True, anti_aliasing_sigma=None):
+        assert isinstance(order, int), "order must be integer."
+        self.output_shape = output_shape
+        self.order = order
+        self.mode = mode
+        self.cval = cval
+        self.clip = clip
+        self.preserve_range = preserve_range
+        self.anti_aliasing = anti_aliasing
+        self.anti_aliasing_sigma = anti_aliasing_sigma
+
+    def __call__(self, img):
+        return resize(img, self.output_shape, order=self.order,
+                      mode=self.mode, cval=self.cval,
+                      clip=self.clip, preserve_range=self.preserve_range,
+                      anti_aliasing=self.anti_aliasing, 
+                      anti_aliasing_sigma=self.anti_aliasing_sigma)
+
+
 @export
 class Rotate:
     """

tests/test_resize.py

@@ -0,0 +1,53 @@
+# Copyright 2020 MONAI Consortium
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#     http://www.apache.org/licenses/LICENSE-2.0
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+
+import numpy as np
+import skimage
+from parameterized import parameterized
+
+from monai.transforms import Resize
+from tests.utils import NumpyImageTestCase2D
+
+
+class ResizeTest(NumpyImageTestCase2D):
+
+    @parameterized.expand([
+        ("invalid_order", "order", AssertionError)
+    ])
+    def test_invalid_inputs(self, _, order, raises):
+        with self.assertRaises(raises):
+            resize = Resize(output_shape=(128, 128, 3), order=order)
+            resize(self.imt)
+
+    @parameterized.expand([
+        ((1, 1, 64, 64), 1, 'reflect', 0, True, True, True, None),
+        ((1, 1, 32, 32), 2, 'constant', 3, False, False, False, None),
+        ((1, 1, 256, 256), 3, 'constant', 3, False, False, False, None),
+    ])
+    def test_correct_results(self, output_shape, order, mode, 
+                             cval, clip, preserve_range, 
+                             anti_aliasing, anti_aliasing_sigma):
+        resize = Resize(output_shape, order, mode, cval, clip, 
+                        preserve_range, anti_aliasing, 
+                        anti_aliasing_sigma)
+        expected = skimage.transform.resize(self.imt, output_shape, 
+                                            order=order, mode=mode, 
+                                            cval=cval, clip=clip, 
+                                            preserve_range=preserve_range, 
+                                            anti_aliasing=anti_aliasing, 
+                                            anti_aliasing_sigma=anti_aliasing_sigma)
+        self.assertTrue(np.allclose(resize(self.imt), expected))
+
+
+if __name__ == '__main__':
+    unittest.main()