padarray

Pad array

Syntax

B = padarray(A,padsize)

B = padarray(A,padsize,padval)

B = padarray(___,direction)

Description

B = padarray(A,padsize) pads array A with an amount of padding in each dimension specified by padsize. The padarray function pads numeric or logical images with the value 0 and categorical images with the category <undefined>. By default, paddarray adds padding before the first element and after the last element of each dimension.

B = padarray(A,padsize,padval) pads array A where padval specifies a constant value to use for padded elements or a method to replicate array elements.

B = padarray(___,direction) pads A in the direction specified by direction.

Examples

Add Padding to 2-D and 3-D Arrays

Pad the Beginning of a Vector

Add three elements of padding to the beginning of a vector with padding value 9.

A = [ 1 2 3 4 ]

A = 1×4

     1     2     3     4

B = padarray(A,3,9,'pre')

B = 4×4

     9     9     9     9
     9     9     9     9
     9     9     9     9
     1     2     3     4

Pad Each Dimension of a 2-D Array

Add three elements of padding to the end of the first dimension of the array and two elements of padding to the end of the second dimension. Use the value of the last array element on each dimension as the padding value.

A = [ 1 2; 3 4 ]

A = 2×2

     1     2
     3     4

B = padarray(A,[3 2],'replicate','post')

B = 5×4

     1     2     2     2
     3     4     4     4
     3     4     4     4
     3     4     4     4
     3     4     4     4

Pad Each Dimension of a 3-D Array

Add three elements of padding to each dimension of a three-dimensional array. Each pad element contains the value 0.

First create the 3-D array.

A = [1 2; 3 4];
B = [5 6; 7 8];
C = cat(3,A,B)

C = 
C(:,:,1) =

     1     2
     3     4


C(:,:,2) =

     5     6
     7     8

Pad the 3-D Array

D = padarray(C,[3 3],0,'both')

D = 
D(:,:,1) =

     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     1     2     0     0     0
     0     0     0     3     4     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0


D(:,:,2) =

     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     5     6     0     0     0
     0     0     0     7     8     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0

Input Arguments

A — Array to be padded

numeric array | logical array | categorical array

Array to be padded, specified as a numeric, logical, or categorical array of any dimension.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | categorical

padsize — Amount of padding

vector of nonnegative integers

Amount of padding to add to each dimension, specified as a vector of nonnegative integers. For example, a padsize value of [2 3] adds two elements of padding along the first dimension and three elements of padding along the second dimension.

Data Types: double

padval — Pad value

0 | numeric scalar | 'circular' | 'replicate' | 'symmetric' | string scalar | character vector | missing

Pad value, specified as one of the following.

Image Type	Format of Fill Values
Numeric image or logical image	Numeric scalar — Pad array with elements of constant value. The default pad value of numeric and logical images is 0. 'circular' — Pad with circular repetition of elements within the dimension. 'replicate' — Pad by repeating border elements of array. 'symmetric' — Pad with mirror reflections of the array along the border.
Categorical image	Valid category in the image, specified as a string scalar or character vector. missing, which corresponds to the <undefined> category. This is the default pad value for categorical images. For more information, see missing.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char | string

direction — Direction to pad array

'both' (default) | 'post' | 'pre'

Direction to pad array along each dimension, specified as one of the following values:

Value	Meaning
'both'	Pads before the first element and after the last array element along each dimension.
'post'	Pad after the last array element along each dimension.
'pre'	Pad before the first array element along each dimension.

Data Types: char | string

Output Arguments

B — Padded array

numeric array | logical array | categorical array

Padded array, returned as an array of the same data type as A.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• padarray supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

• Input arrays of data type categorical are not supported.

• When generating code, padarray supports only up to 3-D inputs

• The input arguments padval and direction must be compile-time constants.

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Usage notes and limitations:

• Input arrays of data type categorical are not supported.

• When generating code, padarray supports only up to 3-D inputs.

• The input arguments padval and direction must be compile-time constants.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

This function fully supports GPU arrays. For more information, see Image Processing on a GPU.