# randomAffine2d

Create randomized 2-D affine transformation

## Description

creates an `tform`

= randomAffine2d`affinetform2d`

object that performs an identity transformation.

specifies the type of affine transformation using name-value arguments.`tform`

= randomAffine2d(`Name,Value`

)

## 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

## 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 = 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.

## See Also

`imwarp`

| `randomWindow2d`

| `centerCropWindow2d`

### Topics

- Augment Images for Deep Learning Workflows (Deep Learning Toolbox)

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