[Telemetry] Migrate bitmap.py from bitmaptools.cc to numpy

tools/telemetry/telemetry/image_processing/histogram.py

Index: tools/telemetry/telemetry/image_processing/histogram.py
diff --git a/tools/telemetry/telemetry/image_processing/histogram.py b/tools/telemetry/telemetry/image_processing/histogram.py
new file mode 100644
index 0000000000000000000000000000000000000000..0fe1029a9ef400ea0c967f431d07117792456cc6
--- /dev/null
+++ b/tools/telemetry/telemetry/image_processing/histogram.py
@@ -0,0 +1,67 @@
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Provides implementations of functions that operate on histograms."""
+
+from __future__ import division
+
+import collections
+
+from telemetry.util import external_modules
+
+np = external_modules.ImportOptionalModule('numpy')
+
+
+def HistogramDistance(hist1, hist2, default_color=None):
+  """Earth mover's distance.
+  http://en.wikipedia.org/wiki/Earth_mover's_distance"""
+  if len(hist1) != len(hist2):
+    raise ValueError('Trying to compare histograms '
+                     'of different sizes, %s != %s' % (len(hist1), len(hist2)))
+  if len(hist1) == 0:
+    return 0
+
+  sum_func = np.sum if np is not None else sum
+
+  n1 = sum_func(hist1)
+  n2 = sum_func(hist2)
+  if (n1 == 0 or n2 == 0) and default_color is None:
+    raise ValueError('Histogram has no data and no default color.')
+  if n1 == 0:
+    hist1[default_color] = 1
+    n1 = 1
+  if n2 == 0:
+    hist2[default_color] = 1
+    n2 = 1
+
+  if np is not None:
+    remainder = np.multiply(hist1, n2) - np.multiply(hist2, n1)
+    cumsum = np.cumsum(remainder)
+    total = np.sum(np.abs(cumsum))
+  else:
+    total = 0
+    remainder = 0
+    for value1, value2 in zip(hist1, hist2):
+      remainder += value1 * n2 - value2 * n1
+      total += abs(remainder)
+    assert remainder == 0, (
+        '%s pixel(s) left over after computing histogram distance.'
+        % abs(remainder))
+  return abs(float(total) / n1 / n2)
+
+
+class ColorHistogram(
+    collections.namedtuple('ColorHistogram', ['r', 'g', 'b', 'default_color'])):
+  # pylint: disable=W0232
+  # pylint: disable=E1002
+
+  def __new__(cls, r, g, b, default_color=None):
+    return super(ColorHistogram, cls).__new__(cls, r, g, b, default_color)
+
+  def Distance(self, other):
+    total = 0
+    for i in xrange(3):
+      default_color = self[3][i] if self[3] is not None else None
+      total += HistogramDistance(self[i], other[i], default_color)
+    return total