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 0s (zeros). padsize is a vector of nonnegative integers that specifies both the amount of padding to add and the dimension along which to add it. The value of an element in the vector specifies the amount of padding to add. The order of the element in the vector specifies the dimension along which to add the padding.

You optionally can perform the padding operation using a GPU (requires Parallel Computing Toolbox™).

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

Array to be padded, specified as a numeric or logical array of any dimension. When padding with a constant value, A must be numeric or logical. When padding using the 'circular', 'replicate', or 'symmetric' methods, A can be of any class.

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

padsize — Amount of padding to add to each dimension

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] means add two elements of padding along the first dimension and three elements of padding along the second dimension. By default, paddarray adds padding before the first element and after the last element along the specified dimension.

Data Types: double

padval — Value to use for the padding

0 (default) | numeric scalar | 'circular' | 'replicate' | 'symmetric'

Value to use for the padding, specified as one of the following.

Value	Meaning
numeric scalar	Pad array with elements of constant value.
'circular'	Pad with circular repetition of elements within the dimension.
'replicate'	Pad by repeating border elements of array.
'symmetric'	Pad array with mirror reflections of itself.

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

direction — Where to pad array along each dimension

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

Where 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

Padded array, returned as a numeric array of the same class 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.

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

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