randomAffine3d

Create randomized 3-D affine transformation

Syntax

tform = randomAffine3d

tform = randomAffine3d(Name,Value)

Description

tform = randomAffine3d creates an affinetform3d object that performs an identity transformation.

tform = randomAffine3d(Name,Value) specifies the type of affine transformation using name-value arguments.

Examples

Randomly Shear 3-D Volume

Create a sample volume.

volumeCube = 0.5*ones(100,100,100);

Create a 3-D viewer to control the appearance of the scene. Set the camera position of the scene to improve the visibility of the volume.

viewer = viewer3d(CameraPosition=[700 -250 650],CameraTarget=[50 50 50]);

Display the volume in the scene.

volshow(volumeCube,Parent=viewer);

Create a 3-D affine transformation that shears 3-D volumes. The randomAffine3d function picks a shear amount randomly from a continuous uniform distribution within the interval [40, 60] degrees. randomAffine3d picks a random shear direction aligned with the x-, y-, or z-axis.

tform1 = randomAffine3d(Shear=[40 60]);
J1 = imwarp(volumeCube,tform1);

Display the sheared volume in a new scene with the same camera position.

viewer1 = viewer3d(CameraPosition=[700 -250 650],CameraTarget=[50 50 50]);
volshow(J1,Parent=viewer1);

To shear a volume by a different randomly selected amount, create a new 3-D affine transformation. Note the difference in the shear direction.

tform2 = randomAffine3d(Shear=[40 60]);
J2 = imwarp(volumeCube,tform2);

Display the sheared volume in a new scene with the same camera position.

viewer2 = viewer3d(CameraPosition=[700 -250 650],CameraTarget=[50 50 50]);
volshow(J2,Parent=viewer2);

Input Arguments

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: tform = randomAffine3d(XReflection=true)

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: tform = randomAffine3d("XReflection",true)

XReflection — Random horizontal reflection

false (default) | true

Random horizontal reflection, specified as false or true. When XReflection is true (1), the transformation tform reflects images horizontally with 50% probability. By default, the transformation does not reflect images in the horizontal direction.

YReflection — Random vertical reflection

false (default) | true

Random vertical reflection, specified as false or true. When YReflection is true (1), the transformation tform reflects images vertically with 50% probability. By default, the transformation does not reflect images in the vertical direction.

ZReflection — Random reflection along depth

false (default) | true

Random reflection along the depth direction, specified as false or true. When ZReflection is true (1), the transformation tform reflects images along the depth direction with 50% probability. By default, the transformation does not reflect images in the depth direction.

Rotation — Range of rotation

[0 0] (default) | 2-element numeric vector | function handle

Range of rotation applied to the input image, specified as one of the following. Rotation is measured in degrees.

• A 2-element numeric vector. The second element must be larger than or equal to the first element. randomAffine3d picks a rotation angle randomly from a continuous uniform distribution within the specified interval. randomAffine3d selects a random axis of rotation from the unit sphere.

• A function handle of the form

  [rotationAxis,theta] = selectRotation

  The function selectRotation must accept no input arguments. The function must return two output arguments: rotationAxis, a 3-element vector defining the axis of rotation, and theta, a rotation angle in degrees.

  Use a function handle to pick rotation angles from a disjoint interval or using a nonuniform probability distribution. You can also use a function handle to specify an axis of rotation. For more information about function handles, see Create Function Handle.

By default, the transformation tform does not rotate images.

Example: [-45 45]

Scale — Range of uniform scaling

[1 1] (default) | 2-element numeric vector | function handle

Range of uniform (isotropic) scaling applied to the input image, specified as one of the following.

• A 2-element numeric vector. The second element must be larger than or equal to the first element. The scale factor is picked randomly from a continuous uniform distribution within the specified interval.

• A function handle. The function must accept no input arguments and return the scale factor as a numeric scalar. Use a function handle to pick scale factors from a disjoint interval or using a nonuniform probability distribution. For more information about function handles, see Create Function Handle.

By default, the transformation tform does not scale images.

Example: [0.5 4]

Shear — Range of shear

[0 0] (default) | 2-element numeric vector | function handle

Range of shear applied to the input image, specified as one of the following. Shear is measured as an angle in degrees, and is in the range (–90, 90).

• A 2-element numeric vector. The second element must be larger than or equal to the first element. The shear angle is picked randomly from a continuous uniform distribution within the specified interval. randomAffine3d applies shear with uniform randomness to one of the principle x-, y-, and z-directions with respect to one of the two possible orthogonal directions.

• A function handle. The function must accept no input arguments and return the shear angle as a numeric scalar. Use a function handle to pick a shear angle from a disjoint interval or using a nonuniform probability distribution. For more information about function handles, see Create Function Handle.

By default, the transformation tform does not shear images in the horizontal direction.

Example: [0 45]

XTranslation — Range of horizontal translation

[0 0] (default) | 2-element numeric vector | function handle

Range of horizontal translation applied to the input image, specified as one of the following. Translation distance is measured in pixels.

• A 2-element numeric vector. The second element must be larger than or equal to the first element. The translation distance is picked randomly from a continuous uniform distribution within the specified interval.

• A function handle. The function must accept no input arguments and return the translation distance as a numeric scalar. Use a function handle to pick a translation distance from a disjoint interval or using a nonuniform probability distribution. For more information about function handles, see Create Function Handle.

By default, the transformation tform does not translate images in the horizontal direction.

Example: [-5 5]

YTranslation — Range of vertical translation

[0 0] (default) | 2-element numeric vector | function handle

Range of vertical translation applied to the input image, specified as one of the following. Translation distance is measured in pixels.

• A 2-element numeric vector. The second element must be larger than or equal to the first element. The translation distance is picked randomly from a continuous uniform distribution within the specified interval.

• A function handle. The function must accept no input arguments and return the translation distance as a numeric scalar. Use a function handle to pick a translation distance from a disjoint interval or using a nonuniform probability distribution. For more information about function handles, see Create Function Handle.

By default, the transformation tform does not translate images in the vertical direction.

Example: [-5 5]

ZTranslation — Range of translation along depth

[0 0] (default) | 2-element numeric vector | function handle

Range of translation along the depth direction applied to the input image, specified as one of the following. Translation distance is measured in pixels.

• A 2-element numeric vector. The second element must be larger than or equal to the first element. The translation distance is picked randomly from a continuous uniform distribution within the specified interval.

• A function handle. The function must accept no input arguments and return the translation distance as a numeric scalar. Use a function handle to pick a translation distance from a disjoint interval or using a nonuniform probability distribution. For more information about function handles, see Create Function Handle.

By default, the transformation tform does not translate images in the depth direction.

Example: [-5 5]

Output Arguments

tform — Affine transformation

affinetform3d object

Affine transformation, returned as an affinetform3d object.

Version History

Introduced in R2019b

R2022b: Returns tform as affinetform3d object

Starting in R2022b, most Image Processing Toolbox™ functions create and perform geometric transformations using the premultiply convention. Accordingly, the randomAffine3d function now returns the output argument tform as an affinetform3d object, which supports the premultiply convention. Before, the function returned tform as an affine3d object, which supports the postmultiply convention. For more information, see Migrate Geometric Transformations to Premultiply Convention.