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# 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.
"""Color Histograms and implementations of functions operating on them."""
from __future__ import division
import collections
from telemetry.internal.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=no-init
# pylint: disable=super-on-old-class
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
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