Improve moments code and use typed memoryviews

skimage/measure/_moments.pyx

@@ -7,50 +7,52 @@ import numpy as np
 cimport numpy as cnp
 
 
-def central_moments(cnp.ndarray[cnp.double_t, ndim=2] array, double cr,
-                    double cc, int order):
+def moments(double[:, :] image, Py_ssize_t order=3):
+    return central_moments(image, 0, 0, order)
+
+
+def central_moments(double[:, :] image, double cr, double cc,
+                    Py_ssize_t order=3):
     cdef Py_ssize_t p, q, r, c
-    cdef cnp.ndarray[cnp.double_t, ndim=2] mu
-    mu = np.zeros((order + 1, order + 1), 'double')
+    cdef double[:, ::1] mu = np.zeros((order + 1, order + 1), dtype=np.double)
     for p in range(order + 1):
         for q in range(order + 1):
-            for r in range(array.shape[0]):
-                for c in range(array.shape[1]):
-                    mu[p,q] += array[r,c] * (r - cr) ** q * (c - cc) ** p
-    return mu
+            for r in range(image.shape[0]):
+                for c in range(image.shape[1]):
+                    mu[p, q] += image[r, c] * (r - cr) ** q * (c - cc) ** p
+    return np.asarray(mu)
 
 
-def normalized_moments(cnp.ndarray[cnp.double_t, ndim=2] mu, int order):
+def normalized_moments(double[:, :] mu, Py_ssize_t order=3):
     cdef Py_ssize_t p, q
-    cdef cnp.ndarray[cnp.double_t, ndim=2] nu
-    nu = np.zeros((order + 1, order + 1), 'double')
+    cdef double[:, ::1] nu = np.zeros((order + 1, order + 1), dtype=np.double)
     for p in range(order + 1):
         for q in range(order + 1):
             if p + q >= 2:
-                nu[p,q] = mu[p,q] / mu[0,0]**(<double>(p + q) / 2 + 1)
+                nu[p,q] = mu[p, q] / mu[0, 0] ** (<double>(p + q) / 2 + 1)
             else:
                 nu[p,q] = np.nan
-    return nu
+    return np.asarray(nu)
 
 
-def hu_moments(cnp.ndarray[cnp.double_t, ndim=2] nu):
-    cdef cnp.ndarray[cnp.double_t, ndim=1] hu = np.zeros((7,), 'double')
-    cdef double t0 = nu[3,0] + nu[1,2]
-    cdef double t1 = nu[2,1] + nu[0,3]
+def hu_moments(double[:, :] nu):
+    cdef double[::1] hu = np.zeros((7, ), dtype=np.double)
+    cdef double t0 = nu[3, 0] + nu[1, 2]
+    cdef double t1 = nu[2, 1] + nu[0, 3]
     cdef double q0 = t0 * t0
     cdef double q1 = t1 * t1
-    cdef double n4 = 4 * nu[1,1]
-    cdef double s = nu[2,0] + nu[0,2]
-    cdef double d = nu[2,0] - nu[0,2]
+    cdef double n4 = 4 * nu[1, 1]
+    cdef double s = nu[2, 0] + nu[0, 2]
+    cdef double d = nu[2, 0] - nu[0, 2]
     hu[0] = s
-    hu[1] = d * d + n4 * nu[1,1]
+    hu[1] = d * d + n4 * nu[1, 1]
     hu[3] = q0 + q1
     hu[5] = d * (q0 - q1) + n4 * t0 * t1
     t0 *= q0 - 3 * q1
     t1 *= 3 * q0 - q1
-    q0 = nu[3,0]- 3 * nu[1,2]
-    q1 = 3 * nu[2,1] - nu[0,3]
+    q0 = nu[3, 0]- 3 * nu[1, 2]
+    q1 = 3 * nu[2, 1] - nu[0, 3]
     hu[2] = q0 * q0 + q1 * q1
     hu[4] = q0 * t0 + q1 * t1
     hu[6] = q1 * t0 - q0 * t1
-    return hu
+    return np.asarray(hu)

skimage/measure/_regionprops.py

@@ -216,7 +216,7 @@ class _RegionProperties(object):
 
     @_cached_property
     def moments(self):
-        return _moments.central_moments(self._image_double, 0, 0, 3)
+        return _moments.moments(self._image_double, 3)
 
     @_cached_property
     def local_centroid(self):