Structural Similarity Index Measure (SSIM)

Module Interface

class torchmetrics.StructuralSimilarityIndexMeasure(gaussian_kernel=True, sigma=1.5, kernel_size=11, reduction='elementwise_mean', data_range=None, k1=0.01, k2=0.03, return_full_image=False, return_contrast_sensitivity=False, **kwargs)

Computes Structual Similarity Index Measure (SSIM).

As input to forward and update the metric accepts the following input

• preds (Tensor): Predictions from model

• target (Tensor): Ground truth values

As output of forward and compute the metric returns the following output

• ssim (Tensor): if reduction!='none' returns float scalar tensor with average SSIM value over sample else returns tensor of shape (N,) with SSIM values per sample

Parameters

• preds – estimated image

• target – ground truth image

• gaussian_kernel (bool) – If True (default), a gaussian kernel is used, if False a uniform kernel is used

• sigma (Union[float, Sequence[float]]) – Standard deviation of the gaussian kernel, anisotropic kernels are possible. Ignored if a uniform kernel is used

• kernel_size (Union[int, Sequence[int]]) – the size of the uniform kernel, anisotropic kernels are possible. Ignored if a Gaussian kernel is used

• reduction (Literal[‘elementwise_mean’, ‘sum’, ‘none’, None]) –

  a method to reduce metric score over individual batch scores

  • 'elementwise_mean': takes the mean

  • 'sum': takes the sum

  • 'none' or None: no reduction will be applied

• data_range (Optional[float]) – Range of the image. If None, it is determined from the image (max - min)

• k1 (float) – Parameter of SSIM.

• k2 (float) – Parameter of SSIM.

• return_full_image (bool) – If true, the full ssim image is returned as a second argument. Mutually exclusive with return_contrast_sensitivity

• return_contrast_sensitivity (bool) – If true, the constant term is returned as a second argument. The luminance term can be obtained with luminance=ssim/contrast Mutually exclusive with return_full_image

• kwargs (Any) – Additional keyword arguments, see Advanced metric settings for more info.

Example

>>> from torchmetrics import StructuralSimilarityIndexMeasure
>>> import torch
>>> preds = torch.rand([3, 3, 256, 256])
>>> target = preds * 0.75
>>> ssim = StructuralSimilarityIndexMeasure(data_range=1.0)
>>> ssim(preds, target)
tensor(0.9219)

Initializes internal Module state, shared by both nn.Module and ScriptModule.

Functional Interface

torchmetrics.functional.structural_similarity_index_measure(preds, target, gaussian_kernel=True, sigma=1.5, kernel_size=11, reduction='elementwise_mean', data_range=None, k1=0.01, k2=0.03, return_full_image=False, return_contrast_sensitivity=False)

Computes Structual Similarity Index Measure.

Parameters

• preds (Tensor) – estimated image

• target (Tensor) – ground truth image

• gaussian_kernel (bool) – If true (default), a gaussian kernel is used, if false a uniform kernel is used

• sigma (Union[float, Sequence[float]]) – Standard deviation of the gaussian kernel, anisotropic kernels are possible. Ignored if a uniform kernel is used

• kernel_size (Union[int, Sequence[int]]) – the size of the uniform kernel, anisotropic kernels are possible. Ignored if a Gaussian kernel is used

• reduction (Literal[‘elementwise_mean’, ‘sum’, ‘none’, None]) –

  a method to reduce metric score over labels.

  • 'elementwise_mean': takes the mean

  • 'sum': takes the sum

  • 'none' or None: no reduction will be applied

• data_range (Optional[float]) – Range of the image. If None, it is determined from the image (max - min)

• k1 (float) – Parameter of SSIM.

• k2 (float) – Parameter of SSIM.

• return_full_image (bool) – If true, the full ssim image is returned as a second argument. Mutually exclusive with return_contrast_sensitivity

• return_contrast_sensitivity (bool) – If true, the constant term is returned as a second argument. The luminance term can be obtained with luminance=ssim/contrast Mutually exclusive with return_full_image

Return type

Union[Tensor, Tuple[Tensor, Tensor]]

Returns

Tensor with SSIM score

Raises

• TypeError – If preds and target don’t have the same data type.

• ValueError – If preds and target don’t have BxCxHxW shape.

• ValueError – If the length of kernel_size or sigma is not 2.

• ValueError – If one of the elements of kernel_size is not an odd positive number.

• ValueError – If one of the elements of sigma is not a positive number.

Example

>>> from torchmetrics.functional import structural_similarity_index_measure
>>> preds = torch.rand([3, 3, 256, 256])
>>> target = preds * 0.75
>>> structural_similarity_index_measure(preds, target)
tensor(0.9219)