ENH Add zernike_moments

This adds a default to the degree and makes radius the first parameter.

Deprecated zernike

ChangeLog

@@ -4,6 +4,7 @@ Version 0.7.2+
 	* Use imread module (if available)
 	* Add output argument to erode() & dilate()
 	* Add 14th Haralick feature (patch by MattyG)
+	* Improved zernike interface (zernike_moments)
 
 Version 0.7.2 2012-02-13 by luispedro
 	* Fix type bug in 32 bit machines (Bug report by Lech Wiktor Piotrowski)

mahotas/features.py

@@ -1,6 +1,6 @@
 from .texture import haralick
 from .tas import tas, pftas
-from .zernike import zernike
+from .zernike import zernike, zernike_moments
 from .lbp import lbp
 
 __all__ = [
@@ -9,4 +9,5 @@
     'pftas',
     'tas',
     'zernike',
+    'zernike_moments',
     ]

mahotas/tests/test_zernike.py

@@ -1,5 +1,5 @@
 import numpy as np
-from mahotas import zernike
+from mahotas.features import zernike_moments
 from mahotas.center_of_mass import center_of_mass
 from math import atan2
 from numpy import cos, sin, conjugate, pi, sqrt
@@ -25,7 +25,7 @@ def _factorial(n):
     v *= (n+1)/pi
     return v 
 
-def _slow_zernike(img, D, radius):
+def _slow_zernike(img, radius, D):
     zvalues = []
 
     Y,X = np.where(img > 0)
@@ -49,7 +49,7 @@ def _slow_zernike(img, D, radius):
 
 def test_zernike():
     A = (np.arange(256) % 14).reshape((16, 16))
-    slow = _slow_zernike(A, 12, 8.)
-    fast = zernike.zernike(A, 12, 8.)
+    slow = _slow_zernike(A, 8., 12)
+    fast = zernike_moments(A, 8., 12)
     delta = np.array(slow) - fast
     assert np.abs(delta).max() < 0.001

mahotas/zernike.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Copyright (C) 2006-2011, Luis Pedro Coelho <luis@luispedro.org>
+# Copyright (C) 2006-2012, Luis Pedro Coelho <luis@luispedro.org>
 # vim: set ts=4 sts=4 sw=4 expandtab smartindent:
 #
 # This program is free software; you can redistribute it and/or modify
@@ -27,25 +27,33 @@
 from center_of_mass import center_of_mass
 import _zernike
 
-__all__ = ['zernike']
+__all__ = ['zernike', 'zernike_moments']
 
-def zernike(img, degree, radius, cm=None):
+def zernike(im, degree, radius, cm=None):
     """
-    zvalues = zernike(img, degree, radius, cm={center_of_mass(img)})
+    zvalues = zernike(im, degree, radius, cm={center_of_mass(im)})
+    """
+    import warnings
+    warnings.warn('mahotas.zernike.zernike: This interface is deprecated. Switch your arguments and use ``zernike_moments``', DeprecationWarning)
+    return zernike_moments(im, radius, degree, cm)
+
+def zernike_moments(im, radius, degree=8, cm=None):
+    """
+    zvalues = zernike_moments(im, radius, degree=8, cm={center_of_mass(im)})
 
     Zernike moments through ``degree``
 
     Returns a vector of absolute Zernike moments through ``degree`` for the
-    image ``img``.
+    image ``im``.
 
     Parameters
     ----------
-    img : 2-ndarray
+    im : 2-ndarray
         input image
-    degree : integer
-        Maximum degree to use
     radius : integer
         the maximum radius for the Zernike polynomials, in pixels
+    degree : integer, optional
+        Maximum degree to use (default: 8)
     cm : pair of floats, optional
         the centre of mass to use. By default, uses the image's centre of mass.
 
@@ -61,12 +69,12 @@ def zernike(img, degree, radius, cm=None):
     """
     zvalues = []
     if cm is None:
-        c0,c1 = center_of_mass(img)
+        c0,c1 = center_of_mass(im)
     else:
         c0,c1 = cm
 
-    Y,X = np.mgrid[:img.shape[0],:img.shape[1]]
-    P = img.ravel()
+    Y,X = np.mgrid[:im.shape[0],:im.shape[1]]
+    P = im.ravel()
 
     def rescale(C, centre):
         Cn = C.astype(np.double)