text: #!/usr/bin/env python
  
  '''
  Coherence-enhancing filtering example
  =====================================
  
  inspired by
    Joachim Weickert "Coherence-Enhancing Shock Filters"
    http://www.mia.uni-saarland.de/Publications/weickert-dagm03.pdf
  '''
  
  import numpy as np
  import cv2
  
  def coherence_filter(img, sigma = 11, str_sigma = 11, blend = 0.5, iter_n = 4):
      h, w = img.shape[:2]
  
      for i in xrange(iter_n):
          print i,
  
          gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
          eigen = cv2.cornerEigenValsAndVecs(gray, str_sigma, 3)
          eigen = eigen.reshape(h, w, 3, 2)  # [[e1, e2], v1, v2]
          x, y = eigen[:,:,1,0], eigen[:,:,1,1]
  
          gxx = cv2.Sobel(gray, cv2.CV_32F, 2, 0, ksize=sigma)
          gxy = cv2.Sobel(gray, cv2.CV_32F, 1, 1, ksize=sigma)
          gyy = cv2.Sobel(gray, cv2.CV_32F, 0, 2, ksize=sigma)
          gvv = x*x*gxx + 2*x*y*gxy + y*y*gyy
          m = gvv < 0
  
          ero = cv2.erode(img, None)
          dil = cv2.dilate(img, None)
          img1 = ero
          img1[m] = dil[m]
          img = np.uint8(img*(1.0 - blend) + img1*blend)
      print 'done'
      return img
  
  
  if __name__ == '__main__':
      import sys
      try: fn = sys.argv[1]
      except: fn = '../cpp/baboon.jpg'
  
      src = cv2.imread(fn)
  
      def nothing(*argv):
          pass
  
      def update():
          sigma = cv2.getTrackbarPos('sigma', 'control')*2+1
          str_sigma = cv2.getTrackbarPos('str_sigma', 'control')*2+1
          blend = cv2.getTrackbarPos('blend', 'control') / 10.0
          print 'sigma: %d  str_sigma: %d  blend_coef: %f' % (sigma, str_sigma, blend)
          dst = coherence_filter(src, sigma=sigma, str_sigma = str_sigma, blend = blend)
          cv2.imshow('dst', dst)
  
      cv2.namedWindow('control', 0)
      cv2.createTrackbar('sigma', 'control', 9, 15, nothing)
      cv2.createTrackbar('blend', 'control', 7, 10, nothing)
      cv2.createTrackbar('str_sigma', 'control', 9, 15, nothing)
  
  
      print 'Press SPACE to update the image\n'
  
      cv2.imshow('src', src)
      update()
      while True:
          ch = 0xFF & cv2.waitKey()
          if ch == ord(' '):
              update()
          if ch == 27:
              break
      cv2.destroyAllWindows()
  