diff --git a/skimage/transform/__init__.py b/skimage/transform/__init__.py index 0907544b..317d8e3d 100644 --- a/skimage/transform/__init__.py +++ b/skimage/transform/__init__.py @@ -4,5 +4,6 @@ from .finite_radon_transform import * from .integral import * from ._geometric import (warp, warp_coords, estimate_transform, SimilarityTransform, AffineTransform, - ProjectiveTransform, PolynomialTransform) -from ._warps import resize, rotate, swirl, homography + ProjectiveTransform, PolynomialTransform, + PiecewiseAffineTransform) +from ._warps import swirl, homography diff --git a/skimage/transform/_geometric.py b/skimage/transform/_geometric.py index 0f76b50e..0aa3d26f 100644 --- a/skimage/transform/_geometric.py +++ b/skimage/transform/_geometric.py @@ -1,6 +1,6 @@ import math import numpy as np -from scipy import ndimage +from scipy import ndimage, spatial from skimage.util import img_as_float from ._warps_cy import _warp_fast @@ -580,6 +580,76 @@ class PolynomialTransform(GeometricTransform): 'parameters by exchanging source and destination coordinates,' 'then apply the forward transformation.') +class PiecewiseAffineTransform(ProjectiveTransform): + + """2D piecewise affine transformation. + + Parameters + ---------- + TODO + + """ + + def __init__(self): + pass + + def estimate(self, src, dst): + + #Convert input to correct types + dstPoints = np.array(dst) + srcPoints = np.array(src) + + #Split input shape into mesh + self.tess = spatial.Delaunay(srcPoints) + + #Calculate ROI in source control points + xmin, xmax = srcPoints[:,0].min(), srcPoints[:,0].max() + ymin, ymax = srcPoints[:,1].min(), srcPoints[:,1].max() + + #Find affine mapping from input positions to mean shape + self.triAffines = [] + for tri in self.tess.vertices: + srcTri = np.hstack((srcPoints[tri,:], np.ones((3,1)))).transpose() + dstTri = np.hstack((dstPoints[tri,:], np.ones((3,1)))).transpose() + + affine = AffineTransform() + affine.estimate(srcTri, dstTri) + self.triAffines.append(affine) + + def __call__(self, coords): + """Apply forward transformation. + + Parameters + ---------- + coords : (N, 2) array + source coordinates + + Returns + ------- + coords : (N, 2) array + Transformed coordinates. + + """ + + out = np.ones((coords.shape[0], 2)) * -1 + + for ptNum, pt in enumerate(coords): + #Determine which triangle contains the point + simplexIndex = self.tess.find_simplex(pt) + + if simplexIndex == -1: + #This point is outside the hull of the control points + out[ptNum,0] = 0 + out[ptNum,1] = 0 + continue + + #Calculate position in the input image + affine = self.triAffines[simplexIndex] + destPos = affine(pt) + out[ptNum,0] = destPos[0][0] + out[ptNum,1] = destPos[0][1] + + return out TRANSFORMS = { 'similarity': SimilarityTransform, @@ -593,7 +663,6 @@ HOMOGRAPHY_TRANSFORMS = ( ProjectiveTransform ) - def estimate_transform(ttype, src, dst, **kwargs): """Estimate 2D geometric transformation parameters.