2D Rotation convenience constructor, Image.rotate_ccw_about_centre

menpo/image/base.py

@@ -9,7 +9,7 @@
 from menpo.base import Vectorizable
 from menpo.landmark import LandmarkableViewable
 from menpo.transform import (Translation, NonUniformScale,
-                             AlignmentUniformScale, Affine)
+                             AlignmentUniformScale, Affine, Rotation)
 from menpo.visualize.base import ImageViewer
 from .interpolation import scipy_interpolation, cython_interpolation
 from .extract_patches import extract_patches_cython
@@ -1238,6 +1238,30 @@ def resize(self, shape, order=1):
         # floating point inaccuracy.
         return self.rescale(scales, round='round', order=order)
 
+    def rotate_ccw_about_centre(self, theta, degrees=True, cval=0):
+        r"""
+        Return a rotation of this image clockwise about it's centre.
+
+        Parameters
+        ----------
+        theta : ``float``
+            The angle of rotation about the origin
+        degrees : ``bool``, optional
+            If true theta is interpreted as a degree. If False, theta is
+            interpreted as radians.
+        cval : ``float``, optional
+            The value to be set outside the rotated image boundaries
+        """
+        if self.n_dims != 2:
+            raise ValueError('Image rotation is presently only supported on '
+                             '2D images')
+        # create a translation that moves the centre of the image to the origin
+        t = Translation(self.centre)
+        r = Rotation.from_2d_ccw_angle(theta, degrees=degrees)
+        r_about_centre = t.pseudoinverse().compose_before(r).compose_before(t)
+        return self.warp_to_shape(self.shape, r_about_centre.pseudoinverse(),
+                                  warp_landmarks=True, cval=cval)
+
     def pyramid(self, n_levels=3, downscale=2):
         image = self
         yield image

menpo/transform/homogeneous/rotation.py

@@ -51,6 +51,30 @@ def __init__(self, rotation_matrix, skip_checks=False):
         Similarity.__init__(self, h_matrix, copy=False, skip_checks=True)
         self.set_rotation_matrix(rotation_matrix, skip_checks=skip_checks)
 
+    @classmethod
+    def from_2d_ccw_angle(cls, theta, degrees=True):
+        r"""
+        Convenience constructor for 2D CCW rotations about the origin
+
+        Parameters
+        ----------
+        theta : float
+            The angle of rotation about the origin
+        degrees : bool, optional
+            If true theta is interpreted as a degree. If False, theta is
+            interpreted as radians.
+
+        Returns
+        -------
+        rotation : :map:`Rotation`
+            A 2D rotation transform.
+        """
+        if degrees:
+            # convert to radians
+            theta = theta * np.pi / 180.0
+        return Rotation(np.array([[np.cos(theta), -np.sin(theta)],
+                                  [np.sin(theta),  np.cos(theta)]]))
+
     @classmethod
     def identity(cls, n_dims):
         return Rotation(np.eye(n_dims))