filter2

2-D digital filter

Syntax

Y = filter2(H,X)

Y = filter2(H,X,shape)

Description

Y = filter2(H,X) applies a finite impulse response filter to a matrix of data X according to coefficients in a matrix H.

Y = filter2(H,X,shape) returns a subsection of the filtered data according to shape. For example, Y = filter2(H,X,'valid') returns only filtered data computed without zero-padded edges.

Examples

2-D Pedestal

You can digitally filter images and other 2-D data using the filter2 function, which is closely related to the conv2 function.

Create and plot a 2-D pedestal with interior height equal to one.

A = zeros(10);
A(3:7,3:7) = ones(5);
mesh(A)

Filter the data in A according to a filter coefficient matrix H, and return the full matrix of filtered data.

H = [1 2 1; 0 0 0; -1 -2 -1];
Y = filter2(H,A,'full');
mesh(Y)

Rotate H 180 degrees and convolve the result with A. The output is equivalent to filtering the data in A with the coefficients in H.

C = conv2(A,rot90(H,2));
mesh(C)

Input Arguments

H — Coefficients of rational transfer function

matrix

Coefficients of the rational transfer function, specified as a matrix.

Data Types: double | single | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical
Complex Number Support: Yes

X — Input data

matrix

Input data, specified as a matrix. If one or both of X and H are of type single, then the output is also of type single. Otherwise, filter2 returns type double.

Data Types: double | single | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical
Complex Number Support: Yes

shape — Subsection of filtered data

'same' (default) | 'full' | 'valid'

Subsection of the filtered data, specified as one of these values:

• 'same' — Return the central part of the filtered data, which is the same size as X.

• 'full' — Return the full 2-D filtered data.

• 'valid' — Return only parts of the filtered data that are computed without zero-padded edges.

Algorithms

The filter2 function filters data by taking the 2-D convolution of the input X and the coefficient matrix H rotated 180 degrees. Specifically, filter2(H,X,shape) is equivalent to conv2(X,rot90(H,2),shape).

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

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

The filter2 function supports GPU array input with these usage notes and limitations:

• The inputs H and X must be single or double arrays. Both real and complex types are supported.

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced before R2006a