added texture_flow.py sample

samples/python2/texture_flow.py

+'''
+Texture flow direction estimation.
+
+Sample shows how cv2.cornerEigenValsAndVecs function can be used 
+to estimate image texture flow direction.
+
+Usage:
+    texture_flow.py [<image>]
+'''
+
+import numpy as np
+import cv2
+
+if __name__ == '__main__':
+    import sys
+    try: fn = sys.argv[1]
+    except: fn = 'data/starry_night.jpg'
+
+    img = cv2.imread(fn)
+    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
+    h, w = img.shape[:2]
+
+    eigen = cv2.cornerEigenValsAndVecs(gray, 15, 3)
+    eigen = eigen.reshape(h, w, 3, 2)  # [[e1, e2], v1, v2]
+    flow = eigen[:,:,2]
+
+    vis = img.copy()
+    vis[:] = (192 + np.uint32(vis)) / 2
+    d = 12
+    points =  np.dstack( np.mgrid[d/2:w:d, d/2:h:d] ).reshape(-1, 2)
+    for x, y in points:
+       vx, vy = np.int32(flow[y, x]*d)
+       cv2.line(vis, (x-vx, y-vy), (x+vx, y+vy), (0, 0, 0), 1, cv2.CV_AA)
+    cv2.imshow('input', img)
+    cv2.imshow('flow', vis)
+    cv2.waitKey()