kornia.geometry.transform#

The functions in this section perform various geometrical transformations of 2D images.

Warp operators#

kornia.geometry.transform.warp_perspective(src, M, dsize, mode='bilinear', padding_mode='zeros', align_corners=True, fill_value=zeros(3))[source]#

Apply a perspective transformation to an image.

https://kornia-tutorials.readthedocs.io/en/latest/_images/warp_perspective_10_1.png

The function warp_perspective transforms the source image using the specified matrix:

\[\text{dst} (x, y) = \text{src} \left( \frac{M^{-1}_{11} x + M^{-1}_{12} y + M^{-1}_{13}}{M^{-1}_{31} x + M^{-1}_{32} y + M^{-1}_{33}} , \frac{M^{-1}_{21} x + M^{-1}_{22} y + M^{-1}_{23}}{M^{-1}_{31} x + M^{-1}_{32} y + M^{-1}_{33}} \right )\]

Parameters

src (Tensor) – input image with shape \((B, C, H, W)\).
M (Tensor) – transformation matrix with shape \((B, 3, 3)\).
dsize (Tuple[int, int]) – size of the output image (height, width).
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection' | 'fill'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True
fill_value (Tensor, optional) – tensor of shape \((3)\) that fills the padding area. Only supported for RGB. Default: zeros(3)

Return type

Tensor

Returns

the warped input image \((B, C, H, W)\).

Example

>>> img = torch.rand(1, 4, 5, 6)
>>> H = torch.eye(3)[None]
>>> out = warp_perspective(img, H, (4, 2), align_corners=True)
>>> print(out.shape)
torch.Size([1, 4, 4, 2])

Note

This function is often used in conjunction with get_perspective_transform().

Note

See a working example here.

kornia.geometry.transform.warp_perspective3d(src, M, dsize, flags='bilinear', border_mode='zeros', align_corners=False)[source]#

Apply a perspective transformation to an image.

The function warp_perspective transforms the source image using the specified matrix:

\[\text{dst} (x, y) = \text{src} \left( \frac{M_{11} x + M_{12} y + M_{13}}{M_{31} x + M_{32} y + M_{33}} , \frac{M_{21} x + M_{22} y + M_{23}}{M_{31} x + M_{32} y + M_{33}} \right )\]

Parameters

src (Tensor) – input image with shape \((B, C, D, H, W)\).
M (Tensor) – transformation matrix with shape \((B, 4, 4)\).
dsize (Tuple[int, int, int]) – size of the output image (height, width).
flags (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
border_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: False

Return type

Tensor

Returns

the warped input image \((B, C, D, H, W)\).

Note

This function is often used in conjunction with get_perspective_transform3d().

kornia.geometry.transform.warp_affine(src, M, dsize, mode='bilinear', padding_mode='zeros', align_corners=True, fill_value=zeros(3))[source]#

Apply an affine transformation to a tensor.

The function warp_affine transforms the source tensor using the specified matrix:

\[\text{dst}(x, y) = \text{src} \left( M_{11} x + M_{12} y + M_{13} , M_{21} x + M_{22} y + M_{23} \right )\]

Parameters

src (Tensor) – input tensor of shape \((B, C, H, W)\).
M (Tensor) – affine transformation of shape \((B, 2, 3)\).
dsize (Tuple[int, int]) – size of the output image (height, width).
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection' | 'fill'. Default: 'zeros'
align_corners (bool, optional) – mode for grid_generation. Default: True
fill_value (Tensor, optional) – tensor of shape \((3)\) that fills the padding area. Only supported for RGB. Default: zeros(3)

Return type

Tensor

Returns

the warped tensor with shape \((B, C, H, W)\).

Note

This function is often used in conjunction with get_rotation_matrix2d(), get_shear_matrix2d(), get_affine_matrix2d(), invert_affine_transform().

Note

See a working example here.

Example

>>> img = torch.rand(1, 4, 5, 6)
>>> A = torch.eye(2, 3)[None]
>>> out = warp_affine(img, A, (4, 2), align_corners=True)
>>> print(out.shape)
torch.Size([1, 4, 4, 2])

kornia.geometry.transform.warp_affine3d(src, M, dsize, flags='bilinear', padding_mode='zeros', align_corners=True)[source]#

Apply a projective transformation a to 3d tensor.

Warning

This API signature it is experimental and might suffer some changes in the future.

Parameters

src (Tensor) – input tensor of shape \((B, C, D, H, W)\).
M (Tensor) – projective transformation matrix of shape \((B, 3, 4)\).
dsize (Tuple[int, int, int]) – size of the output image (depth, height, width).
mode – interpolation mode to calculate output values 'bilinear' | 'nearest'.
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – mode for grid_generation. Default: True

Returns

the warped 3d tensor with shape \((B, C, D, H, W)\).

Return type

Tensor

Note

This function is often used in conjunction with get_perspective_transform3d().

kornia.geometry.transform.warp_image_tps(image, kernel_centers, kernel_weights, affine_weights, align_corners=False)[source]#

Warp an image tensor according to the thin plate spline transform defined by kernel centers, kernel weights, and affine weights.

The transform is applied to each pixel coordinate in the output image to obtain a point in the input image for interpolation of the output pixel. So the TPS parameters should correspond to a warp from output space to input space.

The input image is a \((B, C, H, W)\) tensor. The kernel centers, kernel weight and affine weights are the same as in warp_points_tps.

Parameters

image (Tensor) – input image tensor \((B, C, H, W)\).
kernel_centers (Tensor) – kernel center points \((B, K, 2)\).
kernel_weights (Tensor) – tensor of kernl weights \((B, K, 2)\).
affine_weights (Tensor) – tensor of affine weights \((B, 3, 2)\).
align_corners (bool, optional) – interpolation flag used by grid_sample. Default: False

Return type

Tensor

Returns

warped image tensor \((B, C, H, W)\).

Example

>>> points_src = torch.rand(1, 5, 2)
>>> points_dst = torch.rand(1, 5, 2)
>>> image = torch.rand(1, 3, 32, 32)
>>> # note that we are getting the reverse transform: dst -> src
>>> kernel_weights, affine_weights = get_tps_transform(points_dst, points_src)
>>> warped_image = warp_image_tps(image, points_src, kernel_weights, affine_weights)

Note

This function is often used in conjunction with get_tps_transform().

kornia.geometry.transform.warp_points_tps(points_src, kernel_centers, kernel_weights, affine_weights)[source]#

Warp a tensor of coordinate points using the thin plate spline defined by kernel points, kernel weights, and affine weights.

The source points should be a \((B, N, 2)\) tensor of \((x, y)\) coordinates. The kernel centers are a \((B, K, 2)\) tensor of \((x, y)\) coordinates. The kernel weights are a \((B, K, 2)\) tensor, and the affine weights are a \((B, 3, 2)\) tensor. For the weight tensors, tensor[…, 0] contains the weights for the x-transform and tensor[…, 1] the weights for the y-transform.

Parameters

points_src (Tensor) – tensor of source points \((B, N, 2)\).
kernel_centers (Tensor) – tensor of kernel center points \((B, K, 2)\).
kernel_weights (Tensor) – tensor of kernl weights \((B, K, 2)\).
affine_weights (Tensor) – tensor of affine weights \((B, 3, 2)\).

Return type

Tensor

Returns

The \((B, N, 2)\) tensor of warped source points, from applying the TPS transform.

Example

>>> points_src = torch.rand(1, 5, 2)
>>> points_dst = torch.rand(1, 5, 2)
>>> kernel_weights, affine_weights = get_tps_transform(points_src, points_dst)
>>> warped = warp_points_tps(points_src, points_dst, kernel_weights, affine_weights)
>>> warped_correct = torch.allclose(warped, points_dst)

Note

This function is often used in conjunction with get_tps_transform().

kornia.geometry.transform.remap(image, map_x, map_y, mode='bilinear', padding_mode='zeros', align_corners=None, normalized_coordinates=False)[source]#

Apply a generic geometrical transformation to an image tensor.

The function remap transforms the source tensor using the specified map:

\[\text{dst}(x, y) = \text{src}(map_x(x, y), map_y(x, y))\]

Parameters

image (Tensor) – the tensor to remap with shape (B, C, H, W). Where C is the number of channels.
map_x (Tensor) – the flow in the x-direction in pixel coordinates. The tensor must be in the shape of (B, H, W).
map_y (Tensor) – the flow in the y-direction in pixel coordinates. The tensor must be in the shape of (B, H, W).
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (Optional[bool], optional) – mode for grid_generation. Default: None
normalized_coordinates (bool, optional) – whether the input coordinates are normalized in the range of [-1, 1]. Default: False

Return type

Tensor

Returns

the warped tensor with same shape as the input grid maps.

Example

>>> import torch
>>> from kornia.utils import create_meshgrid
>>> grid = create_meshgrid(2, 2, False)  # 1x2x2x2
>>> grid += 1  # apply offset in both directions
>>> input = torch.ones(1, 1, 2, 2)
>>> remap(input, grid[..., 0], grid[..., 1], align_corners=True)   # 1x1x2x2
tensor([[[[1., 0.],
          [0., 0.]]]])

Note

This function is often used in conjunction with kornia.utils.create_meshgrid().

Image 2d transforms#

kornia.geometry.transform.affine(tensor, matrix, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Apply an affine transformation to the image.

Parameters

tensor (Tensor) – The image tensor to be warped in shapes of \((H, W)\), \((D, H, W)\) and \((B, C, H, W)\).
matrix (Tensor) – The 2x3 affine transformation matrix.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Return type

Tensor

Returns

The warped image with the same shape as the input.

Example

>>> img = torch.rand(1, 2, 3, 5)
>>> aff = torch.eye(2, 3)[None]
>>> out = affine(img, aff)
>>> print(out.shape)
torch.Size([1, 2, 3, 5])

kornia.geometry.transform.rotate(tensor, angle, center=None, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Rotate the tensor anti-clockwise about the center.

Parameters

tensor (Tensor) – The image tensor to be warped in shapes of \((B, C, H, W)\).
angle (Tensor) – The angle through which to rotate. The tensor must have a shape of (B), where B is batch size.
center (Optional[Tensor], optional) – The center through which to rotate. The tensor must have a shape of (B, 2), where B is batch size and last dimension contains cx and cy. Default: None
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Return type

Tensor

Returns

The rotated tensor with shape as input.

Note

See a working example here.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> angle = torch.tensor([90.])
>>> out = rotate(img, angle)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

kornia.geometry.transform.translate(tensor, translation, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Translate the tensor in pixel units.

Parameters

tensor (Tensor) – The image tensor to be warped in shapes of \((B, C, H, W)\).
translation (Tensor) – tensor containing the amount of pixels to translate in the x and y direction. The tensor must have a shape of (B, 2), where B is batch size, last dimension contains dx dy.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Return type

Tensor

Returns

The translated tensor with shape as input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> translation = torch.tensor([[1., 0.]])
>>> out = translate(img, translation)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

kornia.geometry.transform.scale(tensor, scale_factor, center=None, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Scale the tensor by a factor.

Parameters

tensor (Tensor) – The image tensor to be warped in shapes of \((B, C, H, W)\).
scale_factor (Tensor) – The scale factor apply. The tensor must have a shape of (B) or (B, 2), where B is batch size. If (B), isotropic scaling will perform. If (B, 2), x-y-direction specific scaling will perform.
center (Optional[Tensor], optional) – The center through which to scale. The tensor must have a shape of (B, 2), where B is batch size and last dimension contains cx and cy. Default: None
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Return type

Tensor

Returns

The scaled tensor with the same shape as the input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> scale_factor = torch.tensor([[2., 2.]])
>>> out = scale(img, scale_factor)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

kornia.geometry.transform.shear(tensor, shear, mode='bilinear', padding_mode='zeros', align_corners=False)[source]#

Shear the tensor.

Parameters

tensor (Tensor) – The image tensor to be skewed with shape of \((B, C, H, W)\).
shear (Tensor) – tensor containing the angle to shear in the x and y direction. The tensor must have a shape of (B, 2), where B is batch size, last dimension contains shx shy.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: False

Return type

Tensor

Returns

The skewed tensor with shape same as the input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> shear_factor = torch.tensor([[0.5, 0.0]])
>>> out = shear(img, shear_factor)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

kornia.geometry.transform.hflip(input)[source]#

Horizontally flip a tensor image or a batch of tensor images.

Input must be a tensor of shape (C, H, W) or a batch of tensors \((*, C, H, W)\).

Parameters: input (Tensor) – input tensor.
Return type: Tensor
Returns: The horizontally flipped image tensor.

kornia.geometry.transform.vflip(input)[source]#

Vertically flip a tensor image or a batch of tensor images.

Input must be a tensor of shape (C, H, W) or a batch of tensors \((*, C, H, W)\).

Parameters: input (Tensor) – input tensor.
Return type: Tensor
Returns: The vertically flipped image tensor.

kornia.geometry.transform.rot180(input)[source]#

Rotate a tensor image or a batch of tensor images 180 degrees.

Input must be a tensor of shape (C, H, W) or a batch of tensors \((*, C, H, W)\).

Parameters: input (Tensor) – input tensor.
Return type: Tensor
Returns: The rotated image tensor.

kornia.geometry.transform.resize(input, size, interpolation='bilinear', align_corners=None, side='short', antialias=False)[source]#

Resize the input torch.Tensor to the given size.

Parameters

tensor – The image tensor to be skewed with shape of \((..., H, W)\). … means there can be any number of dimensions.
size (Union[int, Tuple[int, int]]) – Desired output size. If size is a sequence like (h, w), output size will be matched to this. If size is an int, smaller edge of the image will be matched to this number. i.e, if height > width, then image will be rescaled to (size * height / width, size)
interpolation (str, optional) – algorithm used for upsampling: 'nearest' | 'linear' | 'bilinear' | ‘bicubic’ | ‘trilinear’ | ‘area’. Default: 'bilinear'
align_corners (Optional[bool], optional) – interpolation flag. Default: None
side (str, optional) – Corresponding side if size is an integer. Can be one of 'short', 'long', 'vert', or 'horz'. Default: 'short'
antialias (bool, optional) – if True, then image will be filtered with Gaussian before downscaling. No effect for upscaling. Default: False

Return type

Tensor

Returns

The resized tensor with the shape as the specified size.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> out = resize(img, (6, 8))
>>> print(out.shape)
torch.Size([1, 3, 6, 8])

kornia.geometry.transform.rescale(input, factor, interpolation='bilinear', align_corners=None, antialias=False)[source]#

Rescale the input torch.Tensor with the given factor.

Parameters

input (Tensor) – The image tensor to be scale with shape of \((B, C, H, W)\).
factor (Union[float, Tuple[float, float]]) – Desired scaling factor in each direction. If scalar, the value is used for both the x- and y-direction.
interpolation (str, optional) – algorithm used for upsampling: 'nearest' | 'linear' | 'bilinear' | 'bicubic' | 'trilinear' | 'area'. Default: 'bilinear'
align_corners (Optional[bool], optional) – interpolation flag. Default: None
side – Corresponding side if size is an integer. Can be one of 'short', 'long', 'vert', or 'horz'.
antialias (bool, optional) – if True, then image will be filtered with Gaussian before downscaling. No effect for upscaling. Default: False

Return type

Tensor

Returns

The rescaled tensor with the shape as the specified size.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> out = rescale(img, (2, 3))
>>> print(out.shape)
torch.Size([1, 3, 8, 12])

kornia.geometry.transform.elastic_transform2d(image, noise, kernel_size=(63, 63), sigma=(32.0, 32.0), alpha=(1.0, 1.0), align_corners=False, mode='bilinear', padding_mode='zeros')[source]#

Apply elastic transform of images as described in [SSP03].

Parameters

image (Tensor) – Input image to be transformed with shape \((B, C, H, W)\).
noise (Tensor) – Noise image used to spatially transform the input image. Same resolution as the input image with shape \((B, 2, H, W)\). The coordinates order it is expected to be in x-y.
kernel_size (Tuple[int, int], optional) – the size of the Gaussian kernel. Default: (63, 63)
sigma (Tuple[float, float], optional) – The standard deviation of the Gaussian in the y and x directions, respectively. Larger sigma results in smaller pixel displacements. Default: (32.0, 32.0)
alpha (Tuple[float, float], optional) – The scaling factor that controls the intensity of the deformation in the y and x directions, respectively. Default: (1.0, 1.0)
align_corners (bool, optional) – Interpolation flag used by `grid_sample`. Default: False
mode (str, optional) – Interpolation mode used by `grid_sample`. Either 'bilinear' or 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – The padding used by `grid_sample`. Either 'zeros', 'border' or 'refection'. Default: 'zeros'

Return type: Tensor
Returns: the elastically transformed input image with shape \((B,C,H,W)\).

Example

>>> image = torch.rand(1, 3, 5, 5)
>>> noise = torch.rand(1, 2, 5, 5, requires_grad=True)
>>> image_hat = elastic_transform2d(image, noise, (3, 3))
>>> image_hat.mean().backward()

>>> image = torch.rand(1, 3, 5, 5)
>>> noise = torch.rand(1, 2, 5, 5)
>>> sigma = torch.tensor([4., 4.], requires_grad=True)
>>> image_hat = elastic_transform2d(image, noise, (3, 3), sigma)
>>> image_hat.mean().backward()

>>> image = torch.rand(1, 3, 5, 5)
>>> noise = torch.rand(1, 2, 5, 5)
>>> alpha = torch.tensor([16., 32.], requires_grad=True)
>>> image_hat = elastic_transform2d(image, noise, (3, 3), alpha=alpha)
>>> image_hat.mean().backward()

kornia.geometry.transform.pyrdown(input, border_type='reflect', align_corners=False, factor=2.0)[source]#

Blur a tensor and downsamples it.

Parameters

input (Tensor) – the tensor to be downsampled.
border_type (str, optional) – the padding mode to be applied before convolving. The expected modes are: 'constant', 'reflect', 'replicate' or 'circular'. Default: 'reflect'
align_corners (bool, optional) – interpolation flag. Default: False
factor (float, optional) – the downsampling factor Default: 2.0

Return type

Tensor

Returns

the downsampled tensor.

Examples

>>> input = torch.arange(16, dtype=torch.float32).reshape(1, 1, 4, 4)
>>> pyrdown(input, align_corners=True)
tensor([[[[ 3.7500,  5.2500],
          [ 9.7500, 11.2500]]]])

kornia.geometry.transform.pyrup(input, border_type='reflect', align_corners=False)[source]#

Upsample a tensor and then blurs it.

Parameters

input (Tensor) – the tensor to be downsampled.
border_type (str, optional) – the padding mode to be applied before convolving. The expected modes are: 'constant', 'reflect', 'replicate' or 'circular'. Default: 'reflect'
align_corners (bool, optional) – interpolation flag. Default: False

Return type

Tensor

Returns

the downsampled tensor.

Examples

>>> input = torch.arange(4, dtype=torch.float32).reshape(1, 1, 2, 2)
>>> pyrup(input, align_corners=True)
tensor([[[[0.7500, 0.8750, 1.1250, 1.2500],
          [1.0000, 1.1250, 1.3750, 1.5000],
          [1.5000, 1.6250, 1.8750, 2.0000],
          [1.7500, 1.8750, 2.1250, 2.2500]]]])

kornia.geometry.transform.build_pyramid(input, max_level, border_type='reflect', align_corners=False)[source]#

Construct the Gaussian pyramid for a tensor image.

The function constructs a vector of images and builds the Gaussian pyramid by recursively applying pyrDown to the previously built pyramid layers.

Parameters

input (Tensor) – the tensor to be used to construct the pyramid.
max_level (int) – 0-based index of the last (the smallest) pyramid layer. It must be non-negative.
border_type (str, optional) – the padding mode to be applied before convolving. The expected modes are: 'constant', 'reflect', 'replicate' or 'circular'. Default: 'reflect'
align_corners (bool, optional) – interpolation flag. Default: False

Return type

List[Tensor]

Shape:

Input: \((B, C, H, W)\)
Output \([(B, C, H, W), (B, C, H/2, W/2), ...]\)

kornia.geometry.transform.build_laplacian_pyramid(input, max_level, border_type='reflect', align_corners=False)[source]#

Construct the Laplacian pyramid for a tensor image.

The function constructs a vector of images and builds the Laplacian pyramid by recursively computing the difference after applying pyrUp to the adjacent layer in it’s Gaussian pyramid.

See [BA87] for more details.

Parameters

input (Tensor) – the tensor to be used to construct the pyramid with shape \((B, C, H, W)\).
max_level (int) – 0-based index of the last (the smallest) pyramid layer. It must be non-negative.
border_type (str, optional) – the padding mode to be applied before convolving. The expected modes are: 'constant', 'reflect', 'replicate' or 'circular'. Default: 'reflect'
align_corners (bool, optional) – interpolation flag. Default: False

Returns

\([(B, C, H, W), (B, C, H/2, W/2), ...]\)

Return type

Output

kornia.geometry.transform.upscale_double(x)[source]#

Upscale image by the factor of 2, even indices maps to original indices.

Odd indices are linearly interpolated from the even ones.

Parameters: x (Tensor) – input image.
Return type: Tensor

Shape:

Input: \((*, H, W)\)
Output \((*, H, W)\)

Matrix transformations#

kornia.geometry.transform.get_perspective_transform(points_src, points_dst)[source]#

Calculate a perspective transform from four pairs of the corresponding points.

The algorithm is a vanilla implementation of the Direct Linear transform (DLT). See more: https://www.cs.cmu.edu/~16385/s17/Slides/10.2_2D_Alignment__DLT.pdf

The function calculates the matrix of a perspective transform that maps from the source to destination points:

\[\begin{split}\begin{bmatrix} x^{'} \\ y^{'} \\ 1 \\ \end{bmatrix} = \begin{bmatrix} h_1 & h_2 & h_3 \\ h_4 & h_5 & h_6 \\ h_7 & h_8 & h_9 \\ \end{bmatrix} \cdot \begin{bmatrix} x \\ y \\ 1 \\ \end{bmatrix}\end{split}\]

Parameters

points_src (Tensor) – coordinates of quadrangle vertices in the source image with shape \((B, 4, 2)\).
points_dst (Tensor) – coordinates of the corresponding quadrangle vertices in the destination image with shape \((B, 4, 2)\).

Return type

Tensor

Returns

the perspective transformation with shape \((B, 3, 3)\).

Note

This function is often used in conjunction with warp_perspective().

Example

>>> x1 = torch.tensor([[[0., 0.], [1., 0.], [1., 1.], [0., 1.]]])
>>> x2 = torch.tensor([[[1., 0.], [0., 0.], [0., 1.], [1., 1.]]])
>>> x2_trans_x1 = get_perspective_transform(x1, x2)

kornia.geometry.transform.get_perspective_transform3d(src, dst)[source]#

Calculate a 3d perspective transform from four pairs of the corresponding points.

The function calculates the matrix of a perspective transform so that:

\[\begin{split}\begin{bmatrix} t_{i}x_{i}^{'} \\ t_{i}y_{i}^{'} \\ t_{i}z_{i}^{'} \\ t_{i} \\ \end{bmatrix} = \textbf{map_matrix} \cdot \begin{bmatrix} x_{i} \\ y_{i} \\ z_{i} \\ 1 \\ \end{bmatrix}\end{split}\]

where

\[dst(i) = (x_{i}^{'},y_{i}^{'},z_{i}^{'}), src(i) = (x_{i}, y_{i}, z_{i}), i = 0,1,2,5,7\]

Concrete math is as below:

\[\[ u_i =\frac{c_{00} * x_i + c_{01} * y_i + c_{02} * z_i + c_{03}} {c_{30} * x_i + c_{31} * y_i + c_{32} * z_i + c_{33}} \] \[ v_i =\frac{c_{10} * x_i + c_{11} * y_i + c_{12} * z_i + c_{13}} {c_{30} * x_i + c_{31} * y_i + c_{32} * z_i + c_{33}} \] \[ w_i =\frac{c_{20} * x_i + c_{21} * y_i + c_{22} * z_i + c_{23}} {c_{30} * x_i + c_{31} * y_i + c_{32} * z_i + c_{33}} \]\]

\[\begin{split}\begin{pmatrix} x_0 & y_0 & z_0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & -x_0*u_0 & -y_0*u_0 & -z_0 * u_0 \\ x_1 & y_1 & z_1 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & -x_1*u_1 & -y_1*u_1 & -z_1 * u_1 \\ x_2 & y_2 & z_2 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & -x_2*u_2 & -y_2*u_2 & -z_2 * u_2 \\ x_5 & y_5 & z_5 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & -x_5*u_5 & -y_5*u_5 & -z_5 * u_5 \\ x_7 & y_7 & z_7 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & -x_7*u_7 & -y_7*u_7 & -z_7 * u_7 \\ 0 & 0 & 0 & 0 & x_0 & y_0 & z_0 & 1 & 0 & 0 & 0 & 0 & -x_0*v_0 & -y_0*v_0 & -z_0 * v_0 \\ 0 & 0 & 0 & 0 & x_1 & y_1 & z_1 & 1 & 0 & 0 & 0 & 0 & -x_1*v_1 & -y_1*v_1 & -z_1 * v_1 \\ 0 & 0 & 0 & 0 & x_2 & y_2 & z_2 & 1 & 0 & 0 & 0 & 0 & -x_2*v_2 & -y_2*v_2 & -z_2 * v_2 \\ 0 & 0 & 0 & 0 & x_5 & y_5 & z_5 & 1 & 0 & 0 & 0 & 0 & -x_5*v_5 & -y_5*v_5 & -z_5 * v_5 \\ 0 & 0 & 0 & 0 & x_7 & y_7 & z_7 & 1 & 0 & 0 & 0 & 0 & -x_7*v_7 & -y_7*v_7 & -z_7 * v_7 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & x_0 & y_0 & z_0 & 1 & -x_0*w_0 & -y_0*w_0 & -z_0 * w_0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & x_1 & y_1 & z_1 & 1 & -x_1*w_1 & -y_1*w_1 & -z_1 * w_1 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & x_2 & y_2 & z_2 & 1 & -x_2*w_2 & -y_2*w_2 & -z_2 * w_2 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & x_5 & y_5 & z_5 & 1 & -x_5*w_5 & -y_5*w_5 & -z_5 * w_5 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & x_7 & y_7 & z_7 & 1 & -x_7*w_7 & -y_7*w_7 & -z_7 * w_7 \\ \end{pmatrix}\end{split}\]

Parameters

src (Tensor) – coordinates of quadrangle vertices in the source image with shape \((B, 8, 3)\).
dst (Tensor) – coordinates of the corresponding quadrangle vertices in the destination image with shape \((B, 8, 3)\).

Return type

Tensor

Returns

the perspective transformation with shape \((B, 4, 4)\).

Note

This function is often used in conjunction with warp_perspective3d().

kornia.geometry.transform.get_projective_transform(center, angles, scales)[source]#

Calculate the projection matrix for a 3D rotation.

Warning

This API signature it is experimental and might suffer some changes in the future.

The function computes the projection matrix given the center and angles per axis.

Parameters

center (Tensor) – center of the rotation (x,y,z) in the source with shape \((B, 3)\).
angles (Tensor) – angle axis vector containing the rotation angles in degrees in the form of (rx, ry, rz) with shape \((B, 3)\). Internally it calls Rodrigues to compute the rotation matrix from axis-angle.
scales (Tensor) – scale factor for x-y-z-directions with shape \((B, 3)\).

Return type

Tensor

Returns

the projection matrix of 3D rotation with shape \((B, 3, 4)\).

Note

This function is often used in conjunction with warp_affine3d().

kornia.geometry.transform.get_rotation_matrix2d(center, angle, scale)[source]#

Calculate an affine matrix of 2D rotation.

The function calculates the following matrix:

\[\begin{split}\begin{bmatrix} \alpha & \beta & (1 - \alpha) \cdot \text{x} - \beta \cdot \text{y} \\ -\beta & \alpha & \beta \cdot \text{x} + (1 - \alpha) \cdot \text{y} \end{bmatrix}\end{split}\]

where

\[\begin{split}\alpha = \text{scale} \cdot cos(\text{angle}) \\ \beta = \text{scale} \cdot sin(\text{angle})\end{split}\]

The transformation maps the rotation center to itself If this is not the target, adjust the shift.

Parameters

center (Tensor) – center of the rotation in the source image with shape \((B, 2)\).
angle (Tensor) – rotation angle in degrees. Positive values mean counter-clockwise rotation (the coordinate origin is assumed to be the top-left corner) with shape \((B)\).
scale (Tensor) – scale factor for x, y scaling with shape \((B, 2)\).

Return type

Tensor

Returns

the affine matrix of 2D rotation with shape \((B, 2, 3)\).

Example

>>> center = zeros(1, 2)
>>> scale = torch.ones((1, 2))
>>> angle = 45. * torch.ones(1)
>>> get_rotation_matrix2d(center, angle, scale)
tensor([[[ 0.7071,  0.7071,  0.0000],
         [-0.7071,  0.7071,  0.0000]]])

Note

This function is often used in conjunction with warp_affine().

kornia.geometry.transform.get_shear_matrix2d(center, sx=None, sy=None)[source]#

Compose shear matrix Bx4x4 from the components.

Note: Ordered shearing, shear x-axis then y-axis.

\[\begin{split}\begin{bmatrix} 1 & b \\ a & ab + 1 \\ \end{bmatrix}\end{split}\]

Parameters

center (Tensor) – shearing center coordinates of (x, y).
sx (Optional[Tensor], optional) – shearing degree along x axis. Default: None
sy (Optional[Tensor], optional) – shearing degree along y axis. Default: None

Returns

params to be passed to the affine transformation with shape \((B, 3, 3)\).

Examples

>>> rng = torch.manual_seed(0)
>>> sx = torch.randn(1)
>>> sx
tensor([1.5410])
>>> center = torch.tensor([[0., 0.]])  # Bx2
>>> get_shear_matrix2d(center, sx=sx)
tensor([[[  1.0000, -33.5468,   0.0000],
         [ -0.0000,   1.0000,   0.0000],
         [  0.0000,   0.0000,   1.0000]]])

Note

This function is often used in conjunction with warp_affine(), warp_perspective().

kornia.geometry.transform.get_shear_matrix3d(center, sxy=None, sxz=None, syx=None, syz=None, szx=None, szy=None)[source]#

Compose shear matrix Bx4x4 from the components. Note: Ordered shearing, shear x-axis then y-axis then z-axis.

\[\begin{split}\begin{bmatrix} 1 & o & r & oy + rz \\ m & p & s & mx + py + sz -y \\ n & q & t & nx + qy + tz -z \\ 0 & 0 & 0 & 1 \\ \end{bmatrix} Where: m = S_{xy} n = S_{xz} o = S_{yx} p = S_{xy}S_{yx} + 1 q = S_{xz}S_{yx} + S_{yz} r = S_{zx} + S_{yx}S_{zy} s = S_{xy}S_{zx} + (S_{xy}S_{yx} + 1)S_{zy} t = S_{xz}S_{zx} + (S_{xz}S_{yx} + S_{yz})S_{zy} + 1\end{split}\]

Params:: center: shearing center coordinates of (x, y, z). sxy: shearing degree along x axis, towards y plane. sxz: shearing degree along x axis, towards z plane. syx: shearing degree along y axis, towards x plane. syz: shearing degree along y axis, towards z plane. szx: shearing degree along z axis, towards x plane. szy: shearing degree along z axis, towards y plane.

Returns: params to be passed to the affine transformation.

Examples

>>> rng = torch.manual_seed(0)
>>> sxy, sxz, syx, syz = torch.randn(4, 1)
>>> sxy, sxz, syx, syz
(tensor([1.5410]), tensor([-0.2934]), tensor([-2.1788]), tensor([0.5684]))
>>> center = torch.tensor([[0., 0., 0.]])  # Bx3
>>> get_shear_matrix3d(center, sxy=sxy, sxz=sxz, syx=syx, syz=syz)
tensor([[[  1.0000,  -1.4369,   0.0000,   0.0000],
         [-33.5468,  49.2039,   0.0000,   0.0000],
         [  0.3022,  -1.0729,   1.0000,   0.0000],
         [  0.0000,   0.0000,   0.0000,   1.0000]]])

Note

This function is often used in conjunction with warp_perspective3d().

kornia.geometry.transform.get_affine_matrix2d(translations, center, scale, angle, sx=None, sy=None)[source]#

Compose affine matrix from the components.

Parameters

translations (Tensor) – tensor containing the translation vector with shape \((B, 2)\).
center (Tensor) – tensor containing the center vector with shape \((B, 2)\).
scale (Tensor) – tensor containing the scale factor with shape \((B, 2)\).
angle (Tensor) – tensor of angles in degrees \((B)\).
sx (Optional[Tensor], optional) – tensor containing the shear factor in the x-direction with shape \((B)\). Default: None
sy (Optional[Tensor], optional) – tensor containing the shear factor in the y-direction with shape \((B)\). Default: None

Return type

Tensor

Returns

the affine transformation matrix \((B, 3, 3)\).

Note

This function is often used in conjunction with warp_affine(), warp_perspective().

kornia.geometry.transform.get_affine_matrix3d(translations, center, scale, angles, sxy=None, sxz=None, syx=None, syz=None, szx=None, szy=None)[source]#

Compose 3d affine matrix from the components.

Parameters

translations (Tensor) – tensor containing the translation vector (dx,dy,dz) with shape \((B, 3)\).
center (Tensor) – tensor containing the center vector (x,y,z) with shape \((B, 3)\).
scale (Tensor) – tensor containing the scale factor with shape \((B)\).
angle – angle axis vector containing the rotation angles in degrees in the form of (rx, ry, rz) with shape \((B, 3)\). Internally it calls Rodrigues to compute the rotation matrix from axis-angle.
sxy (Optional[Tensor], optional) – tensor containing the shear factor in the xy-direction with shape \((B)\). Default: None
sxz (Optional[Tensor], optional) – tensor containing the shear factor in the xz-direction with shape \((B)\). Default: None
syx (Optional[Tensor], optional) – tensor containing the shear factor in the yx-direction with shape \((B)\). Default: None
syz (Optional[Tensor], optional) – tensor containing the shear factor in the yz-direction with shape \((B)\). Default: None
szx (Optional[Tensor], optional) – tensor containing the shear factor in the zx-direction with shape \((B)\). Default: None
szy (Optional[Tensor], optional) – tensor containing the shear factor in the zy-direction with shape \((B)\). Default: None

Return type

Tensor

Returns

the 3d affine transformation matrix \((B, 3, 3)\).

Note

This function is often used in conjunction with warp_perspective().

kornia.geometry.transform.invert_affine_transform(matrix)[source]#

Invert an affine transformation.

The function computes an inverse affine transformation represented by 2×3 matrix:

\[\begin{split}\begin{bmatrix} a_{11} & a_{12} & b_{1} \\ a_{21} & a_{22} & b_{2} \\ \end{bmatrix}\end{split}\]

The result is also a 2×3 matrix of the same type as M.

Parameters: matrix (Tensor) – original affine transform. The tensor must be in the shape of \((B, 2, 3)\).
Return type: Tensor
Returns: the reverse affine transform with shape \((B, 2, 3)\).

Note

This function is often used in conjunction with warp_affine().

kornia.geometry.transform.projection_from_Rt(rmat, tvec)[source]#

Compute the projection matrix from Rotation and translation.

Warning

This API signature it is experimental and might suffer some changes in the future.

Concatenates the batch of rotations and translations such that \(P = [R | t]\).

Parameters

rmat (Tensor) – the rotation matrix with shape \((*, 3, 3)\).
tvec (Tensor) – the translation vector with shape \((*, 3, 1)\).

Return type

Tensor

Returns

the projection matrix with shape \((*, 3, 4)\).

kornia.geometry.transform.get_tps_transform(points_src, points_dst)[source]#

Compute the TPS transform parameters that warp source points to target points.

The input to this function is a tensor of \((x, y)\) source points \((B, N, 2)\) and a corresponding tensor of target \((x, y)\) points \((B, N, 2)\).

Parameters

points_src (Tensor) – batch of source points \((B, N, 2)\) as \((x, y)\) coordinate vectors.
points_dst (Tensor) – batch of target points \((B, N, 2)\) as \((x, y)\) coordinate vectors.

Return type

Tuple[Tensor, Tensor]

Returns

\((B, N, 2)\) tensor of kernel weights and \((B, 3, 2)\): tensor of affine weights. The last dimension contains the x-transform and y-transform weights as separate columns.

Example

>>> points_src = torch.rand(1, 5, 2)
>>> points_dst = torch.rand(1, 5, 2)
>>> kernel_weights, affine_weights = get_tps_transform(points_src, points_dst)

Note

This function is often used in conjunction with warp_points_tps(), warp_image_tps().

Crop operators#

kornia.geometry.transform.crop_by_indices(input_tensor, src_box, size=None, interpolation='bilinear', align_corners=None, antialias=False, shape_compensation='resize')[source]#

Crop tensors with naive indices.

Parameters

input – the 2D image tensor with shape (B, C, H, W).
src_box (Tensor) – a tensor with shape (B, 4, 2) containing the coordinates of the bounding boxes to be extracted. The tensor must have the shape of Bx4x2, where each box is defined in the clockwise order: top-left, top-right, bottom-right and bottom-left. The coordinates must be in x, y order.
size (Optional[Tuple[int, int]], optional) – output size. An auto resize or pad will be performed according to shape_compensation if the cropped slice sizes are not exactly align size. If None, will auto-infer from src_box. Default: None
interpolation (str, optional) – algorithm used for upsampling: 'nearest' | 'linear' | 'bilinear' | ‘bicubic’ | ‘trilinear’ | ‘area’. Default: 'bilinear'
align_corners (Optional[bool], optional) – interpolation flag. Default: None
antialias (bool, optional) – if True, then image will be filtered with Gaussian before downscaling. No effect for upscaling. Default: False
shape_compensation (str, optional) – if the cropped slice sizes are not exactly align size, the image can either be padded or resized. Default: 'resize'

Return type

Tensor

kornia.geometry.transform.crop_by_boxes(input_tensor, src_box, dst_box, mode='bilinear', padding_mode='zeros', align_corners=True, validate_boxes=True)[source]#

Perform crop transform on 2D images (4D tensor) given two bounding boxes.

Given an input tensor, this function selected the interested areas by the provided bounding boxes (src_box). Then the selected areas would be fitted into the targeted bounding boxes (dst_box) by a perspective transformation. So far, the ragged tensor is not supported by PyTorch right now. This function hereby requires the bounding boxes in a batch must be rectangles with same width and height.

Parameters

input_tensor (Tensor) – the 2D image tensor with shape (B, C, H, W).
src_box (Tensor) – a tensor with shape (B, 4, 2) containing the coordinates of the bounding boxes to be extracted. The tensor must have the shape of Bx4x2, where each box is defined in the clockwise order: top-left, top-right, bottom-right and bottom-left. The coordinates must be in x, y order.
dst_box (Tensor) – a tensor with shape (B, 4, 2) containing the coordinates of the bounding boxes to be placed. The tensor must have the shape of Bx4x2, where each box is defined in the clockwise order: top-left, top-right, bottom-right and bottom-left. The coordinates must be in x, y order.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – mode for grid_generation. Default: True
validate_boxes (bool, optional) – flag to perform validation on boxes. Default: True

Returns

the output tensor with patches.

Return type

Tensor

Examples

>>> input = torch.arange(16, dtype=torch.float32).reshape((1, 1, 4, 4))
>>> src_box = torch.tensor([[
...     [1., 1.],
...     [2., 1.],
...     [2., 2.],
...     [1., 2.],
... ]])  # 1x4x2
>>> dst_box = torch.tensor([[
...     [0., 0.],
...     [1., 0.],
...     [1., 1.],
...     [0., 1.],
... ]])  # 1x4x2
>>> crop_by_boxes(input, src_box, dst_box, align_corners=True)
tensor([[[[ 5.0000,  6.0000],
          [ 9.0000, 10.0000]]]])

Note

If the src_box is smaller than dst_box, the following error will be thrown. RuntimeError: solve_cpu: For batch 0: U(2,2) is zero, singular U.

kornia.geometry.transform.center_crop(input_tensor, size, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Crop the 2D images (4D tensor) from the center.

Parameters

input_tensor (Tensor) – the 2D image tensor with shape (B, C, H, W).
size (Tuple[int, int]) – a tuple with the expected height and width of the output patch.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – mode for grid_generation. Default: True

Return type

Tensor

Returns

the output tensor with patches.

Examples

>>> input = torch.tensor([[[
...     [1., 2., 3., 4.],
...     [5., 6., 7., 8.],
...     [9., 10., 11., 12.],
...     [13., 14., 15., 16.],
...  ]]])
>>> center_crop(input, (2, 4), mode='nearest', align_corners=True)
tensor([[[[ 5.,  6.,  7.,  8.],
          [ 9., 10., 11., 12.]]]])

kornia.geometry.transform.crop_and_resize(input_tensor, boxes, size, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Extract crops from 2D images (4D tensor) and resize given a bounding box.

Parameters

input_tensor (Tensor) – the 2D image tensor with shape (B, C, H, W).
boxes (Tensor) – a tensor containing the coordinates of the bounding boxes to be extracted. The tensor must have the shape of Bx4x2, where each box is defined in the following (clockwise) order: top-left, top-right, bottom-right and bottom-left. The coordinates must be in the x, y order. The coordinates would compose a rectangle with a shape of (N1, N2).
size (Tuple[int, int]) – a tuple with the height and width that will be used to resize the extracted patches.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | ‘reflection’. Default: 'zeros'
align_corners (bool, optional) – mode for grid_generation. Default: True

Returns

tensor containing the patches with shape BxCxN1xN2.

Return type

Tensor

Example

>>> input = torch.tensor([[[
...     [1., 2., 3., 4.],
...     [5., 6., 7., 8.],
...     [9., 10., 11., 12.],
...     [13., 14., 15., 16.],
... ]]])
>>> boxes = torch.tensor([[
...     [1., 1.],
...     [2., 1.],
...     [2., 2.],
...     [1., 2.],
... ]])  # 1x4x2
>>> crop_and_resize(input, boxes, (2, 2), mode='nearest', align_corners=True)
tensor([[[[ 6.,  7.],
          [10., 11.]]]])

Module#

class kornia.geometry.transform.Rotate(angle, center=None, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Rotate the tensor anti-clockwise about the centre.

Parameters

angle (Tensor) – The angle through which to rotate. The tensor must have a shape of (B), where B is batch size.
center (Optional[Tensor], optional) – The center through which to rotate. The tensor must have a shape of (B, 2), where B is batch size and last dimension contains cx and cy. Default: None
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Returns

The rotated tensor with the same shape as the input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> angle = torch.tensor([90.])
>>> out = Rotate(angle)(img)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

class kornia.geometry.transform.Translate(translation, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Translate the tensor in pixel units.

Parameters

translation (Tensor) – tensor containing the amount of pixels to translate in the x and y direction. The tensor must have a shape of (B, 2), where B is batch size, last dimension contains dx dy.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Returns

The translated tensor with the same shape as the input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> translation = torch.tensor([[1., 0.]])
>>> out = Translate(translation)(img)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

class kornia.geometry.transform.Scale(scale_factor, center=None, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Scale the tensor by a factor.

Parameters

scale_factor (Tensor) – The scale factor apply. The tensor must have a shape of (B) or (B, 2), where B is batch size. If (B), isotropic scaling will perform. If (B, 2), x-y-direction specific scaling will perform.
center (Optional[Tensor], optional) – The center through which to scale. The tensor must have a shape of (B, 2), where B is batch size and last dimension contains cx and cy. Default: None
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Returns

The scaled tensor with the same shape as the input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> scale_factor = torch.tensor([[2., 2.]])
>>> out = Scale(scale_factor)(img)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

class kornia.geometry.transform.Shear(shear, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Shear the tensor.

Parameters

shear (Tensor) – tensor containing the angle to shear in the x and y direction. The tensor must have a shape of (B, 2), where B is batch size, last dimension contains shx shy.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Returns

The skewed tensor with the same shape as the input.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> shear_factor = torch.tensor([[0.5, 0.0]])
>>> out = Shear(shear_factor)(img)
>>> print(out.shape)
torch.Size([1, 3, 4, 4])

class kornia.geometry.transform.PyrDown(border_type='reflect', align_corners=False, factor=2.0)[source]#

Blur a tensor and downsamples it.

Parameters

border_type (str, optional) – the padding mode to be applied before convolving. The expected modes are: 'constant', 'reflect', 'replicate' or 'circular'. Default: 'reflect'
align_corners (bool, optional) – interpolation flag. Default: False
factor (float, optional) – the downsampling factor Default: 2.0

Returns

the downsampled tensor.

Shape:

Input: \((B, C, H, W)\)
Output: \((B, C, H / 2, W / 2)\)

Examples

>>> input = torch.rand(1, 2, 4, 4)
>>> output = PyrDown()(input)  # 1x2x2x2

class kornia.geometry.transform.PyrUp(border_type='reflect', align_corners=False)[source]#

Upsample a tensor and then blurs it.

Parameters

borde_type – the padding mode to be applied before convolving. The expected modes are: 'constant', 'reflect', 'replicate' or 'circular'.
align_corners (bool, optional) – interpolation flag. Default: False

Returns

the upsampled tensor.

Shape:

Input: \((B, C, H, W)\)
Output: \((B, C, H * 2, W * 2)\)

Examples

>>> input = torch.rand(1, 2, 4, 4)
>>> output = PyrUp()(input)  # 1x2x8x8

class kornia.geometry.transform.ScalePyramid(n_levels=3, init_sigma=1.6, min_size=15, double_image=False)[source]#

Create an scale pyramid of image, usually used for local feature detection.

Images are consequently smoothed with Gaussian blur and downscaled.

Parameters

n_levels (int, optional) – number of the levels in octave. Default: 3
init_sigma (float, optional) – initial blur level. Default: 1.6
min_size (int, optional) – the minimum size of the octave in pixels. Default: 15
double_image (bool, optional) – add 2x upscaled image as 1st level of pyramid. OpenCV SIFT does this. Default: False

Returns

images 2nd output: sigmas (coefficients for scale conversion) 3rd output: pixelDists (coefficients for coordinate conversion)

Return type

1st output

Shape:

Input: \((B, C, H, W)\)
Output 1st: \([(B, C, NL, H, W), (B, C, NL, H/2, W/2), ...]\)
Output 2nd: \([(B, NL), (B, NL), (B, NL), ...]\)
Output 3rd: \([(B, NL), (B, NL), (B, NL), ...]\)

Examples

>>> input = torch.rand(2, 4, 100, 100)
>>> sp, sigmas, pds = ScalePyramid(3, 15)(input)

class kornia.geometry.transform.Hflip[source]#

Horizontally flip a tensor image or a batch of tensor images.

Input must be a tensor of shape (C, H, W) or a batch of tensors \((*, C, H, W)\).

Parameters: input – input tensor.
Returns: The horizontally flipped image tensor.

Examples

>>> hflip = Hflip()
>>> input = torch.tensor([[[
...    [0., 0., 0.],
...    [0., 0., 0.],
...    [0., 1., 1.]
... ]]])
>>> hflip(input)
tensor([[[[0., 0., 0.],
          [0., 0., 0.],
          [1., 1., 0.]]]])

class kornia.geometry.transform.Vflip[source]#

Vertically flip a tensor image or a batch of tensor images.

Input must be a tensor of shape (C, H, W) or a batch of tensors \((*, C, H, W)\).

Parameters: input – input tensor.
Returns: The vertically flipped image tensor.

Examples

>>> vflip = Vflip()
>>> input = torch.tensor([[[
...    [0., 0., 0.],
...    [0., 0., 0.],
...    [0., 1., 1.]
... ]]])
>>> vflip(input)
tensor([[[[0., 1., 1.],
          [0., 0., 0.],
          [0., 0., 0.]]]])

class kornia.geometry.transform.Rot180[source]#

Rotate a tensor image or a batch of tensor images 180 degrees.

Input must be a tensor of shape (C, H, W) or a batch of tensors \((*, C, H, W)\).

Parameters: input – input tensor.

Examples

>>> rot180 = Rot180()
>>> input = torch.tensor([[[
...    [0., 0., 0.],
...    [0., 0., 0.],
...    [0., 1., 1.]
... ]]])
>>> rot180(input)
tensor([[[[1., 1., 0.],
          [0., 0., 0.],
          [0., 0., 0.]]]])

class kornia.geometry.transform.Resize(size, interpolation='bilinear', align_corners=None, side='short', antialias=False)[source]#

Resize the input torch.Tensor to the given size.

Parameters

size (Union[int, Tuple[int, int]]) – Desired output size. If size is a sequence like (h, w), output size will be matched to this. If size is an int, smaller edge of the image will be matched to this number. i.e, if height > width, then image will be rescaled to (size * height / width, size)
interpolation (str, optional) – algorithm used for upsampling: 'nearest' | 'linear' | 'bilinear' | ‘bicubic’ | ‘trilinear’ | ‘area’. Default: 'bilinear'
align_corners (Optional[bool], optional) – interpolation flag. Default: None
side (str, optional) – Corresponding side if size is an integer. Can be one of 'short', 'long', 'vert', or 'horz'. Default: 'short'
antialias (bool, optional) – if True, then image will be filtered with Gaussian before downscaling. No effect for upscaling. Default: False

Returns

The resized tensor with the shape of the given size.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> out = Resize((6, 8))(img)
>>> print(out.shape)
torch.Size([1, 3, 6, 8])

class kornia.geometry.transform.Rescale(factor, interpolation='bilinear', align_corners=True, antialias=False)[source]#

Rescale the input torch.Tensor with the given factor.

Parameters

factor (Union[float, Tuple[float, float]]) – Desired scaling factor in each direction. If scalar, the value is used for both the x- and y-direction.
interpolation (str, optional) – algorithm used for upsampling: 'nearest' | 'linear' | 'bilinear' | 'bicubic' | 'trilinear' | 'area'. Default: 'bilinear'
align_corners (bool, optional) – interpolation flag. Default: True
side – Corresponding side if size is an integer. Can be one of 'short', 'long', 'vert', or 'horz'.
antialias (bool, optional) – if True, then image will be filtered with Gaussian before downscaling. No effect for upscaling. Default: False

Returns

The rescaled tensor with the shape according to the given factor.

Example

>>> img = torch.rand(1, 3, 4, 4)
>>> out = Rescale((2, 3))(img)
>>> print(out.shape)
torch.Size([1, 3, 8, 12])

class kornia.geometry.transform.Affine(angle=None, translation=None, scale_factor=None, shear=None, center=None, mode='bilinear', padding_mode='zeros', align_corners=True)[source]#

Apply multiple elementary affine transforms simultaneously.

Parameters

angle (Optional[Tensor], optional) – Angle in degrees for counter-clockwise rotation around the center. The tensor must have a shape of (B), where B is the batch size. Default: None
translation (Optional[Tensor], optional) – Amount of pixels for translation in x- and y-direction. The tensor must have a shape of (B, 2), where B is the batch size and the last dimension contains dx and dy. Default: None
scale_factor (Optional[Tensor], optional) – Factor for scaling. The tensor must have a shape of (B), where B is the batch size. Default: None
shear (Optional[Tensor], optional) – Angles in degrees for shearing in x- and y-direction around the center. The tensor must have a shape of (B, 2), where B is the batch size and the last dimension contains sx and sy. Default: None
center (Optional[Tensor], optional) – Transformation center in pixels. The tensor must have a shape of (B, 2), where B is the batch size and the last dimension contains cx and cy. Defaults to the center of image to be transformed. Default: None
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
align_corners (bool, optional) – interpolation flag. Default: True

Raises

RuntimeError – If not one of angle, translation, scale_factor, or shear is set.

Returns

The transformed tensor with same shape as input.

Example

>>> img = torch.rand(1, 2, 3, 5)
>>> angle = 90. * torch.rand(1)
>>> out = Affine(angle)(img)
>>> print(out.shape)
torch.Size([1, 2, 3, 5])

class kornia.geometry.transform.HomographyWarper(height, width, mode='bilinear', padding_mode='zeros', normalized_coordinates=True, align_corners=False)[source]#

Warp tensors by homographies.

\[X_{dst} = H_{src}^{\{dst\}} * X_{src}\]

Parameters

height (int) – The height of the destination tensor.
width (int) – The width of the destination tensor.
mode (str, optional) – interpolation mode to calculate output values 'bilinear' | 'nearest'. Default: 'bilinear'
padding_mode (str, optional) – padding mode for outside grid values 'zeros' | 'border' | 'reflection'. Default: 'zeros'
normalized_coordinates (bool, optional) – whether to use a grid with normalized coordinates. Default: True
align_corners (bool, optional) – interpolation flag. Default: False

Image registration#

class kornia.geometry.transform.image_registrator.Homography[source]#

Homography geometric model to be used together with ImageRegistrator module for the optimization-based image registration.

forward()[source]#

Single-batch homography”.

Return type: Tensor
Returns: Homography matrix with shape \((1, 3, 3)\).

forward_inverse()[source]#

Interted Single-batch homography”.

Return type: Tensor
Returns: Homography martix with shape \((1, 3, 3)\).

reset_model()[source]#: Initializes the model with identity transform.

class kornia.geometry.transform.image_registrator.ImageRegistrator(model_type='homography', optimizer=optim.Adam, loss_fn=F.l1_loss, pyramid_levels=5, lr=0.001, num_iterations=100, tolerance=0.0001, warper=None)[source]#

Module, which performs optimization-based image registration.

Parameters

model_type (optional) – Geometrical model for registration. Can be string or Module. Default: 'homography'
optimizer (optional) – optimizer class used for the optimization. Default: optim.Adam
loss_fn (Callable[..., Tensor], optional) – torch loss function. Default: F.l1_loss
pyramid_levels (int, optional) – number of scale pyramid levels. Default: 5
lr (float, optional) – learning rate for optimization. Default: 0.001
num_iterations (int, optional) – maximum number of iterations. Default: 100
tolerance (float, optional) – stop optimizing if loss difference is less. default 1e-4. Default: 0.0001
warper (optional) – if model_type is not string, one needs to provide warper object. Default: None

Example

>>> from kornia.geometry import ImageRegistrator
>>> img_src = torch.rand(1, 1, 32, 32)
>>> img_dst = torch.rand(1, 1, 32, 32)
>>> registrator = ImageRegistrator('similarity')
>>> homo = registrator.register(img_src, img_dst)

get_single_level_loss(img_src, img_dst, transform_model)[source]#

Warp img_src into img_dst with transform_model and returns loss.

Return type: Tensor

register(src_img, dst_img, verbose=False, output_intermediate_models=False)[source]#

Estimate the tranformation’ which warps src_img into dst_img by gradient descent. The shape of the tensors is not checked, because it may depend on the model, e.g. volume registration.

Parameters

src_img (Tensor) – Input image tensor.
dst_img (Tensor) – Input image tensor.
verbose (bool, optional) – if True, outputs loss every 10 iterations. Default: False
output_intermediate_models (bool, optional) – if True with intermediate models Default: False

Return type

Union[Tensor, Tuple[Tensor, List[Tensor]]]

Returns

the transformation between two images, shape depends on the model, typically [1x3x3] tensor for string model_types.

reset_model()[source]#

Calls model reset function.

Return type: None

warp_dst_inro_src(dst_img)[source]#

Warp src_img with inverted estimated model.

Return type: Tensor

warp_src_into_dst(src_img)[source]#

Warp src_img with estimated model.

Return type: Tensor

class kornia.geometry.transform.image_registrator.Similarity(rotation=True, scale=True, shift=True)[source]#

Similarity geometric model to be used together with ImageRegistrator module for the optimization-based image registration.

Parameters

rotation (bool, optional) – if True, the rotation is optimizable, else constant zero. Default: True
scale (bool, optional) – if True, the scale is optimizable, else constant zero. Default: True
shift (bool, optional) – if True, the shift is optimizable, else constant one. Default: True

forward()[source]#

Single-batch similarity transform”.

Return type: Tensor
Returns: Similarity with shape \((1, 3, 3)\)

forward_inverse()[source]#

Single-batch inverse similarity transform”.

Return type: Tensor
Returns: Similarity with shape \((1, 3, 3)\)

reset_model()[source]#

Initialize the model with identity transform.

Return type: None

kornia.geometry.transform#

Warp operators#

Image 2d transforms#

Matrix transformations#

Crop operators#

Module#

Image registration#

Interactive Demo#