Source code for pysteg.features.ale

##  $Id$
## -*- coding: utf-8 -*-

"""
:Module:    pysteg.features.ale
:Date:      $Date$
:Revision:  $Revision$
:Author:    © 2012: Hans Georg Schaathun <georg@schaathun.net>
"""

from .cm import cooccurrence
import numpy as np

__all__ = [ "ale1d", "ale2d" ]

# 1D ALE features
# ===============

def alepts(h,S):
   """
   Return a list of local extrema on the histogram h
   restricted to the set S.
   """
   return [ x for x in S if (h[x] - h[x-1])*(h[x] - h[x+1]) > 0 ]
def alef1(h,E):
   "Calculate the ALE feature based on the list E of local extrema."
   return sum( [ abs(2*h[x] - h[x-1] - h[x+1]) for x in E ] )
def ale1d(I):
   """Return the first-order ALE features f_1 and f_2."""
   if I == None:
      return [ "ALE1D-f1", "ALE1D-f2", ]
   h = np.histogram(I.flatten(),bins=list(xrange(257)))[0]
   E1 = alepts(h,xrange(3,253))
   f1 = alef1(h,E1)
   E2 = alepts(h,[1,2,253,254])
   f2 = alef1(h,E2)
   return [f1,f2]
def ale0(I):
   """Return the original ALE feature f_0."""
   h = np.histogram(I.flatten(),bins=list(xrange(257)))[0]
   E0 = alepts(h,xrange(1,255))
   f0 = alef1(h,E0)
   return f0

# 2D ALE features
# ===============

def andf(x,y):
   return x&y

def ale2d(I,dir=None):
   """Return the second-order ALE features for the given direction dir."""
   if dir == None:
      L = [ ale2d(I,d) for d in [ "h", "v", "d", "m" ] ]
      return reduce( list.__add__, L )
   if I == None:
      return [ "ALE2D-%s-A" % (dir,), "ALE2D-%s-d" % (dir,), ]
   h = cooccurrence(I,dir)[0]
   A = h[1:-1,1:-1]
   AT = [h[:-2,1:-1],h[2:,1:-1],h[1:-1,:-2],h[1:-1,2:]]
   T  = reduce( andf, [ ( A < x ) for x in AT ] )
   T |= reduce( andf, [ ( A > x ) for x in AT ] )
   T &= T.transpose()
   X = sum( np.abs(4*A[T] - sum( [ x[T] for x in AT ] )) )
   (M,N) = h.shape
   assert M == N
   d = sum( [ h[k,k] for k in xrange(M) ] )
   return [X,d]