--- a
+++ b/helpers.py
@@ -0,0 +1,75 @@
+import numpy as np
+import matplotlib
+from matplotlib import pyplot as plt
+import cv2
+from PIL import Image, ImageDraw
+
+
+def pop_and_add(l, val, max_length):
+    if len(l) == max_length:
+        l.pop(0)
+    l.append(val)
+
+
+def last_ip(ips):
+    for i, ip in enumerate(reversed(ips)):
+        if ip is not None:
+            return ip, len(ips) - i
+
+def last_valid_hist(ips):
+    for i,ip in enumerate(reversed(ips)):
+        if valid_candidate_hist(ip):
+            return ip
+
+def dist(ip1, ip2):
+    ip1 = ip1["keypoints"]
+    ip2 = ip2["keypoints"]
+    return np.sqrt(np.sum((ip1['N']-ip2['N'])**2 + (ip1['B']-ip2['B'])**2))
+
+
+def move_figure(f, x, y):
+    """Move figure's upper left corner to pixel (x, y)"""
+    backend = matplotlib.get_backend()
+    if backend == 'TkAgg':
+        f.canvas.manager.window.wm_geometry("+%d+%d" % (x, y))
+    elif backend == 'WXAgg':
+        f.canvas.manager.window.SetPosition((x, y))
+    else:
+        # This works for QT and GTK
+        # You can also use window.setGeometry
+        f.canvas.manager.window.move(x, y)
+
+def valid_candidate_hist(ip):
+    if ip is not None:
+        return ip["up_hist"] is not None
+    else:
+        return False
+
+def dist_hist(ips1,ips2):
+
+    ip1 = last_valid_hist(ips1)
+    ip2 = last_valid_hist(ips2)
+
+    uhist1 = ip1["up_hist"]
+    uhist2 = ip2["up_hist"]
+
+    assert uhist1 is not None
+    assert uhist2 is not None
+
+    assert type(uhist1) == np.ndarray
+
+    return np.sum(np.absolute(uhist1-uhist2))
+
+def get_hist(img, bbox, nbins=3):
+
+    if not np.any(bbox):
+        return None
+
+    mask = Image.new('L', (img.shape[1], img.shape[0]), 0)
+    ImageDraw.Draw(mask).polygon(list(bbox.flatten()), outline=1, fill=1)
+    mask = np.array(mask)
+    hist = cv2.calcHist([img], [0, 1], mask, [nbins, 2*nbins], [0, 180, 0, 256])
+    cv2.normalize(hist, hist, alpha=1, norm_type=cv2.NORM_L1)
+
+
+    return hist