Added GIL-release code into python wrappers

Added gabor_threads.py sample

samples/python2/gabor_threads.py

@@ -0,0 +1,67 @@
+'''
+gabor_threads.py
+=========
+
+Sample demonstrates:
+- use of multiple Gabor filter convolutions to get Fractalius-like image effect (http://www.redfieldplugins.com/filterFractalius.htm)
+- use of python threading to accelerate the computation
+
+Usage
+-----
+gabor_threads.py [image filename]
+
+'''
+
+import numpy as np
+import cv2
+from threading import Lock
+from multiprocessing.pool import ThreadPool
+            
+
+def build_filters():
+    filters = []
+    ksize = 31
+    for theta in np.arange(0, np.pi, np.pi / 16):
+        kern = cv2.getGaborKernel((ksize, ksize), 4.0, theta, 10.0, 0.5, 0, ktype=cv2.CV_32F)
+        kern /= 1.5*kern.sum()
+        filters.append(kern)
+    return filters
+
+def process(img, filters):
+    accum = np.zeros_like(img)
+    for kern in filters:
+        fimg = cv2.filter2D(img, cv2.CV_8UC3, kern)
+        np.maximum(accum, fimg, accum)
+    return accum
+
+def process_threaded(img, filters, threadn = 8):
+    accum = np.zeros_like(img)
+    accum_lock = Lock()
+    def f(kern):
+        fimg = cv2.filter2D(img, cv2.CV_8UC3, kern)
+        with accum_lock:
+            np.maximum(accum, fimg, accum)
+    pool = ThreadPool(processes=threadn)
+    pool.map(f, filters)
+    return accum
+
+if __name__ == '__main__':
+    import sys
+    from common import Timer
+    
+    print __doc__
+    try: img_fn = sys.argv[1]
+    except: img_fn = '../cpp/baboon.jpg'
+
+    img = cv2.imread(img_fn)
+    filters = build_filters() 
+
+    with Timer('running single-threaded'):
+        res1 = process(img, filters)
+    with Timer('running multi-threaded'):
+        res2 = process_threaded(img, filters)
+    
+    print 'res1 == res2: ', (res1 == res2).all()
+    cv2.imshow('img', img)
+    cv2.imshow('result', res2)
+    cv2.waitKey()