def compare_pngs(actual, expected):
    """ Compare two images using RMS approach.
    
    Actual and expected are paths to PNG files.
    
    Returns True for mismatch, False otherwise.
    """

    # open the image files and remove the alpha channel (if it exists)
    expectedImage = _png.read_png_int(expected)
    actualImage = _png.read_png_int(actual)
    expectedImage = expectedImage[:, :, :3]
    actualImage = actualImage[:, :, :3]

    # convert to signed integers, so that the images can be subtracted without
    # overflow
    expectedImage = expectedImage.astype(np.int16)
    actualImage = actualImage.astype(np.int16)

    num_values = np.prod(expectedImage.shape)
    abs_diff_image = abs(expectedImage - actualImage)

    histogram = np.bincount(abs_diff_image.ravel(), minlength=256)

    sum_of_squares = np.sum(histogram * np.arange(len(histogram)) ** 2)
    rms = np.sqrt(float(sum_of_squares) / num_values)
    
    return rms

def test_imread_png_uint16():
    from matplotlib import _png
    img = _png.read_png_int(os.path.join(os.path.dirname(__file__),
                                         'baseline_images/test_png/uint16.png'))

    assert (img.dtype == np.uint16)
    assert np.sum(img.flatten()) == 134184960

def compare_images(expected, actual, tol, in_decorator=False):
    """
    Compare two "image" files checking differences within a tolerance.

    The two given filenames may point to files which are convertible to
    PNG via the `.converter` dictionary. The underlying RMS is calculated
    with the `.calculate_rms` function.

    Parameters
    ----------
    expected : str
        The filename of the expected image.
    actual :str
        The filename of the actual image.
    tol : float
        The tolerance (a color value difference, where 255 is the
        maximal difference).  The test fails if the average pixel
        difference is greater than this value.
    in_decorator : bool
        If called from image_comparison decorator, this should be
        True. (default=False)

    Example
    -------
    img1 = "./baseline/plot.png"
    img2 = "./output/plot.png"
    compare_images( img1, img2, 0.001 ):

    """
    if not os.path.exists(actual):
        msg = "Output image %s does not exist." % actual
        raise Exception(msg)

    if os.stat(actual).st_size == 0:
        msg = "Output image file %s is empty." % actual
        raise Exception(msg)

    verify(actual)

    # Convert the image to png
    extension = expected.split('.')[-1]

    if not os.path.exists(expected):
        raise IOError('Baseline image %r does not exist.' % expected)

    if extension != 'png':
        actual = convert(actual, False)
        expected = convert(expected, True)

    # open the image files and remove the alpha channel (if it exists)
    expectedImage = _png.read_png_int(expected)
    actualImage = _png.read_png_int(actual)
    expectedImage = expectedImage[:, :, :3]
    actualImage = actualImage[:, :, :3]

    actualImage, expectedImage = crop_to_same(
        actual, actualImage, expected, expectedImage)

    # convert to signed integers, so that the images can be subtracted without
    # overflow
    expectedImage = expectedImage.astype(np.int16)
    actualImage = actualImage.astype(np.int16)

    rms = calculate_rms(expectedImage, actualImage)

    diff_image = make_test_filename(actual, 'failed-diff')

    if rms <= tol:
        if os.path.exists(diff_image):
            os.unlink(diff_image)
        return None

    save_diff_image(expected, actual, diff_image)

    results = dict(rms=rms, expected=str(expected),
                   actual=str(actual), diff=str(diff_image))

    if not in_decorator:
        # Then the results should be a string suitable for stdout.
        template = ['Error: Image files did not match.',
                    'RMS Value: {rms}',
                    'Expected:  \n    {expected}',
                    'Actual:    \n    {actual}',
                    'Difference:\n    {diff}',
                    'Tolerance: \n    {tol}', ]
        results = '\n  '.join([line.format(**results) for line in template])
    return results

def compare_images( expected, actual, tol, in_decorator=False ):
   '''Compare two image files - not the greatest, but fast and good enough.

   = EXAMPLE

   # img1 = "./baseline/plot.png"
   # img2 = "./output/plot.png"
   #
   # compare_images( img1, img2, 0.001 ):

   = INPUT VARIABLES
   - expected  The filename of the expected image.
   - actual    The filename of the actual image.
   - tol       The tolerance (a color value difference, where 255 is the
               maximal difference).  The test fails if the average pixel
               difference is greater than this value.
   - in_decorator If called from image_comparison decorator, this should be
               True. (default=False)
   '''

   verify(actual)

   # Convert the image to png
   extension = expected.split('.')[-1]

   if not os.path.exists(expected):
       raise IOError('Baseline image %r does not exist.' % expected)

   if extension != 'png':
      actual = convert(actual, False)
      expected = convert(expected, True)

   # open the image files and remove the alpha channel (if it exists)
   expectedImage = _png.read_png_int( expected )
   actualImage = _png.read_png_int( actual )
   expectedImage = expectedImage[:, :, :3]
   actualImage = actualImage[:, :, :3]

   actualImage, expectedImage = crop_to_same(actual, actualImage, expected, expectedImage)

   # convert to signed integers, so that the images can be subtracted without
   # overflow
   expectedImage = expectedImage.astype(np.int16)
   actualImage = actualImage.astype(np.int16)

   rms = calculate_rms(expectedImage, actualImage)

   diff_image = make_test_filename(actual, 'failed-diff')

   if rms <= tol:
      if os.path.exists(diff_image):
         os.unlink(diff_image)
      return None

   save_diff_image( expected, actual, diff_image )

   if in_decorator:
      results = dict(
         rms = rms,
         expected = str(expected),
         actual = str(actual),
         diff = str(diff_image),
         )
      return results
   else:
      # old-style call from mplTest directory
      msg = "  Error: Image files did not match.\n"       \
            "  RMS Value: " + str( rms ) + "\n" \
            "  Expected:\n    " + str( expected ) + "\n"  \
            "  Actual:\n    " + str( actual ) + "\n"      \
            "  Difference:\n    " + str( diff_image ) + "\n"      \
            "  Tolerance: " + str( tol ) + "\n"
      return msg

def compare_images( expected, actual, tol, in_decorator=False ):
   '''Compare two image files - not the greatest, but fast and good enough.

   = EXAMPLE

   # img1 = "./baseline/plot.png"
   # img2 = "./output/plot.png"
   #
   # compare_images( img1, img2, 0.001 ):

   = INPUT VARIABLES
   - expected  The filename of the expected image.
   - actual    The filename of the actual image.
   - tol       The tolerance (a color value difference, where 255 is the
               maximal difference).  The test fails if the average pixel
               difference is greater than this value.
   - in_decorator If called from image_comparison decorator, this should be
               True. (default=False)
   '''

   verify(actual)

   # Convert the image to png
   extension = expected.split('.')[-1]

   if not os.path.exists(expected):
       raise IOError('Baseline image %r does not exist.' % expected)

   if extension != 'png':
      actual = convert(actual, False)
      expected = convert(expected, True)

   # open the image files and remove the alpha channel (if it exists)
   expectedImage = _png.read_png_int( expected )
   actualImage = _png.read_png_int( actual )
   expectedImage = expectedImage[:, :, :3]
   actualImage = actualImage[:, :, :3]

   actualImage, expectedImage = crop_to_same(actual, actualImage, expected, expectedImage)

   # convert to signed integers, so that the images can be subtracted without
   # overflow
   expectedImage = expectedImage.astype(np.int16)
   actualImage = actualImage.astype(np.int16)

   # compare the resulting image histogram functions
   expected_version = version.LooseVersion("1.6")
   found_version = version.LooseVersion(np.__version__)

   # On Numpy 1.6, we can use bincount with minlength, which is much faster than
   # using histogram
   if found_version >= expected_version:
      rms = 0

      for i in xrange(0, 3):
         h1p = expectedImage[:,:,i]
         h2p = actualImage[:,:,i]

         h1h = np.bincount(h1p.ravel(), minlength=256)
         h2h = np.bincount(h2p.ravel(), minlength=256)

         rms += np.sum(np.power((h1h-h2h), 2))
   else:
      rms = 0
      ns = np.arange(257)

      for i in xrange(0, 3):
         h1p = expectedImage[:,:,i]
         h2p = actualImage[:,:,i]

         h1h = np.histogram(h1p, bins=ns)[0]
         h2h = np.histogram(h2p, bins=ns)[0]

         rms += np.sum(np.power((h1h-h2h), 2))

   rms = calculate_rms(expectedImage, actualImage)

   diff_image = make_test_filename(actual, 'failed-diff')

   if rms <= tol:
      if os.path.exists(diff_image):
         os.unlink(diff_image)
      return None

   save_diff_image( expected, actual, diff_image )

   if in_decorator:
      results = dict(
         rms = rms,
         expected = str(expected),
         actual = str(actual),
         diff = str(diff_image),
         )
      return results
   else:
      # old-style call from mplTest directory
      msg = "  Error: Image files did not match.\n"       \
            "  RMS Value: " + str( rms ) + "\n" \
            "  Expected:\n    " + str( expected ) + "\n"  \
            "  Actual:\n    " + str( actual ) + "\n"      \
#.........这里部分代码省略.........

def compare_images( expected, actual, tol, in_decorator=False ):
   '''Compare two image files - not the greatest, but fast and good enough.

   = EXAMPLE

   # img1 = "./baseline/plot.png"
   # img2 = "./output/plot.png"
   #
   # compare_images( img1, img2, 0.001 ):

   = INPUT VARIABLES
   - expected  The filename of the expected image.
   - actual    The filename of the actual image.
   - tol       The tolerance (a unitless float).  This is used to
               determine the 'fuzziness' to use when comparing images.
   - in_decorator If called from image_comparison decorator, this should be
               True. (default=False)
   '''

   verify(actual)

   # Convert the image to png
   extension = expected.split('.')[-1]
   if extension != 'png':
      actual = convert(actual, False)
      expected = convert(expected, True)

   # open the image files and remove the alpha channel (if it exists)
   expectedImage = _png.read_png_int( expected )
   actualImage = _png.read_png_int( actual )

   actualImage, expectedImage = crop_to_same(actual, actualImage, expected, expectedImage)

   # compare the resulting image histogram functions
   expected_version = version.LooseVersion("1.6")
   found_version = version.LooseVersion(np.__version__)

   # On Numpy 1.6, we can use bincount with minlength, which is much faster than
   # using histogram
   if found_version >= expected_version:
      rms = 0

      for i in xrange(0, 3):
         h1p = expectedImage[:,:,i]
         h2p = actualImage[:,:,i]

         h1h = np.bincount(h1p.ravel(), minlength=256)
         h2h = np.bincount(h2p.ravel(), minlength=256)

         rms += np.sum(np.power((h1h-h2h), 2))
   else:
      rms = 0
      bins = np.arange(257)

      for i in xrange(0, 3):
         h1p = expectedImage[:,:,i]
         h2p = actualImage[:,:,i]

         h1h = np.histogram(h1p, bins=bins)[0]
         h2h = np.histogram(h2p, bins=bins)[0]

         rms += np.sum(np.power((h1h-h2h), 2))

   rms = np.sqrt(rms / (256 * 3))

   diff_image = make_test_filename(actual, 'failed-diff')

   if ( (rms / 10000.0) <= tol ):
      if os.path.exists(diff_image):
         os.unlink(diff_image)
      return None

   save_diff_image( expected, actual, diff_image )

   if in_decorator:
      results = dict(
         rms = rms,
         expected = str(expected),
         actual = str(actual),
         diff = str(diff_image),
         )
      return results
   else:
      # old-style call from mplTest directory
      msg = "  Error: Image files did not match.\n"       \
            "  RMS Value: " + str( rms / 10000.0 ) + "\n" \
            "  Expected:\n    " + str( expected ) + "\n"  \
            "  Actual:\n    " + str( actual ) + "\n"      \
            "  Difference:\n    " + str( diff_image ) + "\n"      \
            "  Tolerance: " + str( tol ) + "\n"
      return msg

def compare_images(expected, actual, tol, in_decorator=False):
    """
    Compare two "image" files checking differences within a tolerance.

    The two given filenames may point to files which are convertible to
    PNG via the `.converter` dictionary. The underlying RMS is calculated
    with the `.calculate_rms` function.

    Parameters
    ----------
    expected : str
        The filename of the expected image.
    actual : str
        The filename of the actual image.
    tol : float
        The tolerance (a color value difference, where 255 is the
        maximal difference).  The test fails if the average pixel
        difference is greater than this value.
    in_decorator : bool
        Determines the output format. If called from image_comparison
        decorator, this should be True. (default=False)

    Returns
    -------
    comparison_result : None or dict or str
        Return *None* if the images are equal within the given tolerance.

        If the images differ, the return value depends on  *in_decorator*.
        If *in_decorator* is true, a dict with the following entries is
        returned:

        - *rms*: The RMS of the image difference.
        - *expected*: The filename of the expected image.
        - *actual*: The filename of the actual image.
        - *diff_image*: The filename of the difference image.
        - *tol*: The comparison tolerance.

        Otherwise, a human-readable multi-line string representation of this
        information is returned.

    Examples
    --------
    ::

        img1 = "./baseline/plot.png"
        img2 = "./output/plot.png"
        compare_images(img1, img2, 0.001)

    """
    from matplotlib import _png

    if not os.path.exists(actual):
        raise Exception("Output image %s does not exist." % actual)

    if os.stat(actual).st_size == 0:
        raise Exception("Output image file %s is empty." % actual)

    # Convert the image to png
    extension = expected.split('.')[-1]

    if not os.path.exists(expected):
        raise IOError('Baseline image %r does not exist.' % expected)

    if extension != 'png':
        actual = convert(actual, False)
        expected = convert(expected, True)

    # open the image files and remove the alpha channel (if it exists)
    expected_image = _png.read_png_int(expected)
    actual_image = _png.read_png_int(actual)
    expected_image = expected_image[:, :, :3]
    actual_image = actual_image[:, :, :3]

    actual_image, expected_image = crop_to_same(
        actual, actual_image, expected, expected_image)

    diff_image = make_test_filename(actual, 'failed-diff')

    if tol <= 0:
        if np.array_equal(expected_image, actual_image):
            return None

    # convert to signed integers, so that the images can be subtracted without
    # overflow
    expected_image = expected_image.astype(np.int16)
    actual_image = actual_image.astype(np.int16)

    rms = calculate_rms(expected_image, actual_image)

    if rms <= tol:
        return None

    save_diff_image(expected, actual, diff_image)

    results = dict(rms=rms, expected=str(expected),
                   actual=str(actual), diff=str(diff_image), tol=tol)

    if not in_decorator:
        # Then the results should be a string suitable for stdout.
        template = ['Error: Image files did not match.',
#.........这里部分代码省略.........

def compare_images( expected, actual, tol, in_decorator=False ):
   '''Compare two image files - not the greatest, but fast and good enough.

   = EXAMPLE

   # img1 = "./baseline/plot.png"
   # img2 = "./output/plot.png"
   #
   # compare_images( img1, img2, 0.001 ):

   = INPUT VARIABLES
   - expected  The filename of the expected image.
   - actual    The filename of the actual image.
   - tol       The tolerance (a unitless float).  This is used to
               determine the 'fuzziness' to use when comparing images.
   - in_decorator If called from image_comparison decorator, this should be
               True. (default=False)
   '''

   verify(actual)

   # Convert the image to png
   extension = expected.split('.')[-1]
   if extension != 'png':
      actual = convert(actual, False)
      expected = convert(expected, True)

   # open the image files and remove the alpha channel (if it exists)
   expectedImage = _png.read_png_int( expected )
   actualImage = _png.read_png_int( actual )

   actualImage, expectedImage = crop_to_same(actual, actualImage, expected, expectedImage)

   # compare the resulting image histogram functions
   expected_version = version.LooseVersion("1.6")
   found_version = version.LooseVersion(np.__version__)

   rms = calculate_rms(expectedImage, actualImage)

   diff_image = make_test_filename(actual, 'failed-diff')

   if ( (rms / 10000.0) <= tol ):
      if os.path.exists(diff_image):
         os.unlink(diff_image)
      return None

   # For Agg-rendered images, we can retry by ignoring pixels with
   # differences of only 1
   if extension == 'png':
       # Remove differences of only 1
       diffImage = np.abs(np.asarray(actualImage, dtype=np.int) -
                          np.asarray(expectedImage, dtype=np.int))
       actualImage = np.where(diffImage <= 1, expectedImage, actualImage)

       rms = calculate_rms(expectedImage, actualImage)

       if ( (rms / 10000.0) <= tol ):
           if os.path.exists(diff_image):
               os.unlink(diff_image)
           return None

   save_diff_image( expected, actual, diff_image )

   if in_decorator:
      results = dict(
         rms = rms,
         expected = str(expected),
         actual = str(actual),
         diff = str(diff_image),
         )
      return results
   else:
      # old-style call from mplTest directory
      msg = "  Error: Image files did not match.\n"       \
            "  RMS Value: " + str( rms / 10000.0 ) + "\n" \
            "  Expected:\n    " + str( expected ) + "\n"  \
            "  Actual:\n    " + str( actual ) + "\n"      \
            "  Difference:\n    " + str( diff_image ) + "\n"      \
            "  Tolerance: " + str( tol ) + "\n"
      return msg