Source code for viqa.fr_metrics.msssim

"""Module for calculating the multiscale structural similarity index (MS-SSIM) between
two images.

Examples
--------
    .. doctest-skip::

        >>> import numpy as np
        >>> from viqa import MSSSIM
        >>> img_r = np.random.rand(256, 256)
        >>> img_m = np.random.rand(256, 256)
        >>> msssim = MSSSIM()
        >>> msssim.score(img_r, img_m, data_range=1)

"""

# Authors
# -------
# Author: Lukas Behammer
# Research Center Wels
# University of Applied Sciences Upper Austria, 2023
# CT Research Group
#
# Modifications
# -------------
# Original code, 2024, Lukas Behammer
#
# License
# -------
# BSD-3-Clause License

from warnings import warn

import numpy as np
from piq import multi_scale_ssim
from torch import tensor

from viqa._metrics import FullReferenceMetricsInterface
from viqa.utils import _check_chromatic


[docs] class MSSSIM(FullReferenceMetricsInterface): """Calculate the multiscale structural similarity index (MS-SSIM) between two images. Attributes ---------- score_val : float MS-SSIM score value of the last calculation. parameters : dict Dictionary containing the parameters for MS-SSIM calculation. Parameters ---------- data_range : {1, 255, 65535}, default=255 Data range of the returned data in data loading. Is used for image loading when ``normalize`` is True and for the MS-SSIM calculation. Passed to :py:func:`viqa.utils.load_data` and :py:meth:`score`. normalize : bool, default=False If True, the input images are normalized to the ``data_range`` argument. **kwargs : optional Additional parameters for data loading. The keyword arguments are passed to :py:func:`.viqa.utils.load_data`. Other Parameters ---------------- chromatic : bool, default False If True, the input images are expected to be RGB images. .. note:: Color images can be used, but it is unclear how the called implementation :py:func:`piq.multi_scale_ssim` handles the color channels. Raises ------ ValueError If ``data_range`` is not set. Warnings -------- This metric is not yet tested. The metric should be only used for experimental purposes. .. todo:: test Notes ----- For more information on the MS-SSIM metric, see [1]_. See Also -------- viqa.fr_metrics.uqi.UQI : Universal quality index (UQI) between two images. viqa.fr_metrics.ssim.SSIM : Structural similarity index (SSIM) between two images. References ---------- .. [1] Wang, Z., Simoncelli, E. P., & Bovik, A. C. (2003). Multi-scale structural similarity for image quality assessment. The Thirty-Seventh Asilomar Conference on Signals, Systems & Computers, 1298–1402. https://doi.org/10.1109/ACSSC.2003.1292216 """ def __init__(self, data_range=255, normalize=False, **kwargs): """Construct method.""" if data_range is None: raise ValueError("Parameter data_range must be set.") super().__init__(data_range=data_range, normalize=normalize, **kwargs) self._name = "MS-SSIM"
[docs] def score(self, img_r, img_m, dim=None, im_slice=None, **kwargs): """ Calculate the multiscale structural similarity index (MS-SSIM) between two images. Parameters ---------- img_r : np.ndarray or Tensor or str or os.PathLike Reference image to calculate score against. img_m : np.ndarray or Tensor or str or os.PathLike Distorted image to calculate score of. dim : {0, 1, 2}, optional MS-SSIM for 3D images is calculated as mean over all slices of the given dimension. im_slice : int, optional If given, MS-SSIM is calculated only for the given slice of the 3D image. **kwargs : optional Additional parameters for MS-SSIM calculation. The keyword arguments are passed to :py:func:`piq.multi_scale_ssim`. See the documentation under [2]_. Other Parameters ---------------- kernel_size : int, default=11 The side-length of the sliding window used in comparison. Must be an odd value. kernel_sigma : float, default=1.5 Sigma of normal distribution. reduction : str, default='mean' Specifies the reduction type: 'none', 'mean' or 'sum'. scale_weights : list, default=[0.0448, 0.2856, 0.3001, 0.2363, 0.1333] Weights for different scales. k1 : float, default=0.01 Algorithm parameter, K1 (small constant, see [3]_). k2 : float, default=0.03 Algorithm parameter, K2 (small constant, see [3]_). Try a larger K2 constant (e.g. 0.4) if you get a negative or NaN results. .. seealso:: See :py:func:`.viqa.fr_metrics.ssim.structural_similarity` for more information Returns ------- score_val : float MS-SSIM score value. Raises ------ ValueError If invalid dimension given in ``dim``. \n If images are neither 2D nor 3D. \n If images are 3D, but dim is not given. \n If ``im_slice`` is given, but not an integer. Warns ----- RuntimeWarning If ``dim`` or ``im_slice`` is given for 2D images. \n If ``im_slice`` is not given, but ``dim`` is given for 3D images, MS-SSIM is calculated for the full volume. Notes ----- For 3D images if ``dim`` is given, but ``im_slice`` is not, the MS-SSIM is calculated for the full volume of the 3D image. This is implemented as `mean` of the MS-SSIM values of all slices of the given dimension. If ``dim`` is given and ``im_slice`` is given, the MS-SSIM is calculated for the given slice of the given dimension (represents a 2D metric of the given slice). References ---------- .. [2] https://piq.readthedocs.io/en/latest/functions.html#piq.multi_scale_ssim .. [3] Wang, Z., Simoncelli, E. P., & Bovik, A. C. (2003). Multi-scale structural similarity for image quality assessment. The Thirty-Seventh Asilomar Conference on Signals, Systems & Computers, 1298–1402. https://doi.org/10.1109/ACSSC.2003.1292216 """ img_r, img_m = self.load_images(img_r, img_m) if "scale_weights" in kwargs and type(kwargs["scale_weights"]) is list: kwargs["scale_weights"] = tensor(kwargs["scale_weights"]) if img_r.ndim == 3 and img_r.shape[-1] != 3: if ( dim is not None and type(im_slice) is int ): # if dim and im_slice are given # Calculate MS-SSIM for given slice of given dimension match dim: case 0: img_r_tensor, img_m_tensor = _check_chromatic( img_r[im_slice, :, :], img_m[im_slice, :, :], self.parameters["chromatic"], ) score_val = multi_scale_ssim( img_r_tensor, img_m_tensor, data_range=self.parameters["data_range"], **kwargs, ) case 1: img_r_tensor, img_m_tensor = _check_chromatic( img_r[:, im_slice, :], img_m[:, im_slice, :], self.parameters["chromatic"], ) score_val = multi_scale_ssim( img_r_tensor, img_m_tensor, data_range=self.parameters["data_range"], **kwargs, ) case 2: img_r_tensor, img_m_tensor = _check_chromatic( img_r[:, :, im_slice], img_m[:, :, im_slice], self.parameters["chromatic"], ) score_val = multi_scale_ssim( img_r_tensor, img_m_tensor, data_range=self.parameters["data_range"], **kwargs, ) case _: raise ValueError( "Invalid dim value. Must be integer of 0, 1 or 2." ) elif ( dim is not None and im_slice is None ): # if dim is given, but im_slice is not, calculate MS-SSIM for full # volume warn( "im_slice is not given. Calculating MS-SSIM for full volume.", RuntimeWarning, ) img_r_tensor, img_m_tensor = _check_chromatic( img_r, img_m, self.parameters["chromatic"], ) score_val = multi_scale_ssim( img_r_tensor, img_m_tensor, data_range=self.parameters["data_range"], **kwargs, ) else: if type(im_slice) is not int or None: raise ValueError("im_slice must be an integer.") raise ValueError( "If images are 3D, dim and im_slice (optional) must be given." ) elif img_r.ndim == 2 or (img_r.ndim == 3 and img_r.shape[-1] == 3): if dim or im_slice: warn("dim and im_slice are ignored for 2D images.", RuntimeWarning) # Calculate MS-SSIM for 2D images img_r_tensor, img_m_tensor = _check_chromatic( img_r, img_m, self.parameters["chromatic"], ) score_val = multi_scale_ssim( img_r_tensor, img_m_tensor, data_range=self.parameters["data_range"], **kwargs, ) else: raise ValueError("Images must be 2D or 3D.") self.score_val = float(score_val) return score_val
[docs] def print_score(self, decimals=2): """Print the MSSSIM score value of the last calculation. Parameters ---------- decimals : int, default=2 Number of decimal places to print the score value. Warns ----- RuntimeWarning If :py:attr:`score_val` is not available. """ if self.score_val is not None: print("MS-SSIM: {}".format(np.round(self.score_val, decimals))) else: print("No score value for MS-SSIM. Run score() first.")