randomAffine2d

Create randomized 2-D affine transformation

Syntax

tform = randomAffine2d

tform = randomAffine2d(Name,Value)

Description

tform = randomAffine2d creates an affinetform2d object that performs an identity transformation.

tform = randomAffine2d(Name,Value) specifies the type of affine transformation using name-value arguments.

Examples

Rotate Image by Random Angle

Read and display an image.

I = imread("kobi.png");
imshow(I)

Create a 2-D affine transformation object that rotates images. The randomAffine2d function picks the rotation angle randomly from a continuous uniform distribution within the interval [35, 55] degrees.

tform1 = randomAffine2d(Rotation=[35 55]);

Rotate the image and display the result.

J = imwarp(I,tform1);
imshow(J)

The transformation object, tform1, rotates all images by the same amount. To rotate an image by a different randomly selected amount, create a new geometric transformation.

tform2 = randomAffine2d(Rotation=[-10 10]);
J2 = imwarp(I,tform2);
imshow(J2)

Randomly Rotate Image with Custom Rotation Range

Read and display an image.

I = imread("sherlock.jpg");
imshow(I)

Create a 2-D affine transformation object that rotates images. To select a rotation angle from a custom range, specify the Rotation name-value argument as a function handle. This example specifies a function called myrange (defined at the end of the example) that selects an angle from within two disjoint intervals.

tform = randomAffine2d(Rotation=@myrange);

Rotate the image and display the result.

J = imwarp(I,tform);
imshow(J)

Supporting Function

This example defines the myrange function that first randomly selects one of two intervals (-10, 10) and (170, 190) with equal probability. Within the selected interval, the function returns a single random number from a uniform distribution.

function angle = myrange()
    if randi([0 1],1)
        a = -10;
        b = 10;
    else
        a = 170;
        b = 190;
    end
    angle = a + (b-a).*rand(1);
end

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 = randomAffine2d(XReflection=true)

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

Example: tform = randomAffine2d("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.

Rotation — Range of rotation

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

Range of rotation, in degrees, 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 rotation angle 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 rotation angle as a numeric scalar. Use a function handle to pick rotation angles 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 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]

XShear — Range of horizontal shear

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

Range of horizontal 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 horizontal shear angle 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 horizontal shear angle as a numeric scalar. Use a function handle to pick horizontal shear angles 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]

YShear — Range of vertical shear

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

Range of vertical 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 vertical shear angle 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 vertical shear angle as a numeric scalar. Use a function handle to pick vertical shear angles 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 vertical 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 horizontal 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 horizontal translation distance as a numeric scalar. Use a function handle to pick horizontal translation distances 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 vertical 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 vertical translation distance as a numeric scalar. Use a function handle to pick vertical translation distances 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]

Output Arguments

tform — Affine transformation

affinetform2d object

Affine transformation, returned as an affinetform2d object.

Version History

Introduced in R2019b

R2022b: Returns tform as affinetform2d object

Starting in R2022b, most Image Processing Toolbox™ functions create and perform geometric transformations using the premultiply convention. Accordingly, the randomAffine2d function now returns the output argument tform as an affinetform2d object, which supports the premultiply convention. Before, the function returned tform as an affine2d object, which supports the postmultiply convention. For more information, see Migrate Geometric Transformations to Premultiply Convention.