message: Added a statement that the arguments `img1` and `img2` accept only positive values.
  Fixes
diff: @@ -4285,9 +4285,9 @@ def ssim(img1,
  Args:
  img1: First image batch. 4-D Tensor of shape `[batch, height, width,
  - channels]`.
  + channels]` with only Positive Pixel Values.
  img2: Second image batch. 4-D Tensor of shape `[batch, height, width,
  - channels]`.
  + channels]` with only Positive Pixel Values.
  max_val: The dynamic range of the images (i.e., the difference between the
  maximum the and minimum allowed values).
  filter_size: Default value 11 (size of gaussian filter).
  @@ -4350,8 +4350,9 @@ def ssim_multiscale(img1,
  Computers, 2004.
  Args:
  - img1: First image batch.
  - img2: Second image batch. Must have the same rank as img1.
  + img1: First image batch with only Positive Pixel Values.
  + img2: Second image batch with only Positive Pixel Values. Must have the
  + same rank as img1.
  max_val: The dynamic range of the images (i.e., the difference between the
  maximum the and minimum allowed values).
  power_factors: Iterable of weights for each of the scales. The number of
  