MATLAB Function Reference |

Two-dimensional digital filtering

**Syntax**

**Description**

filters the data in `Y = filter2(h,X)`

`X`

with the two-dimensional FIR filter in the matrix `h`

. It computes the result, `Y`

, using two-dimensional correlation, and returns the central part of the correlation that is the same size as `X`

.

returns the part of `Y = filter2(h,X,`

*shape*`)`

`Y`

specified by the `shape`

parameter.

is a string with one of these values:*shape*

**Remarks**

Two-dimensional correlation is equivalent to two-dimensional convolution with the filter matrix rotated 180 degrees. See the Algorithm section for more information about how `filter2`

performs linear filtering.

**Algorithm**

Given a matrix `X`

and a two-dimensional FIR filter `h`

, `filter2`

rotates your filter matrix 180 degrees to create a convolution kernel. It then calls `conv2`

, the two-dimensional convolution function, to implement the filtering operation.

`filter2`

uses `conv2`

to compute the full two-dimensional convolution of the FIR filter with the input matrix. By default, `filter2`

then extracts the central part of the convolution that is the same size as the input matrix, and returns this as the result. If the `shape`

parameter specifies an alternate part of the convolution for the result, `filter2`

returns the appropriate part.

**See Also**

filter | find |