msssim.py 文件源码

def MultiScaleSSIM(img1, img2, max_val=255, filter_size=11, filter_sigma=1.5,
                   k1=0.01, k2=0.03, weights=None):
  """Return the MS-SSIM score between `img1` and `img2`.
  This function implements Multi-Scale Structural Similarity (MS-SSIM) Image
  Quality Assessment according to Zhou Wang's paper, "Multi-scale structural
  similarity for image quality assessment" (2003).
  Link: https://ece.uwaterloo.ca/~z70wang/publications/msssim.pdf
  Author's MATLAB implementation:
  http://www.cns.nyu.edu/~lcv/ssim/msssim.zip
  Arguments:
    img1: Numpy array holding the first RGB image batch.
    img2: Numpy array holding the second RGB image batch.
    max_val: the dynamic range of the images (i.e., the difference between the
      maximum the and minimum allowed values).
    filter_size: Size of blur kernel to use (will be reduced for small images).
    filter_sigma: Standard deviation for Gaussian blur kernel (will be reduced
      for small images).
    k1: Constant used to maintain stability in the SSIM calculation (0.01 in
      the original paper).
    k2: Constant used to maintain stability in the SSIM calculation (0.03 in
      the original paper).
    weights: List of weights for each level; if none, use five levels and the
      weights from the original paper.
  Returns:
    MS-SSIM score between `img1` and `img2`.
  Raises:
    RuntimeError: If input images don't have the same shape or don't have four
      dimensions: [batch_size, height, width, depth].
  """
  if img1.shape != img2.shape:
    raise RuntimeError('Input images must have the same shape (%s vs. %s).',
                       img1.shape, img2.shape)
  if img1.ndim != 4:
    raise RuntimeError('Input images must have four dimensions, not %d',
                       img1.ndim)

  # Note: default weights don't sum to 1.0 but do match the paper / matlab code.
  weights = np.array(weights if weights else
                     [0.0448, 0.2856, 0.3001, 0.2363, 0.1333])
  levels = weights.size
  downsample_filter = np.ones((1, 2, 2, 1)) / 4.0
  im1, im2 = [x.astype(np.float64) for x in [img1, img2]]
  mssim = np.array([])
  mcs = np.array([])
  for _ in range(levels):
    ssim, cs = _SSIMForMultiScale(
        im1, im2, max_val=max_val, filter_size=filter_size,
        filter_sigma=filter_sigma, k1=k1, k2=k2)
    mssim = np.append(mssim, ssim)
    mcs = np.append(mcs, cs)
    filtered = [convolve(im, downsample_filter, mode='reflect')
                for im in [im1, im2]]
    im1, im2 = [x[:, ::2, ::2, :] for x in filtered]
  return (np.prod(mcs[0:levels-1] ** weights[0:levels-1]) *
          (mssim[levels-1] ** weights[levels-1]))