nlfilter (Image Processing Toolbox)

Perform general sliding-neighborhood operations

Syntax

B = nlfilter(A,[m n],fun)
B = nlfilter(A,[m n],fun,P1,P2,...)
B = nlfilter(A,'indexed',...)

Description

B = nlfilter(A,[m n],fun) applies the function fun to each m-by-n sliding block of A. fun is a function that accepts an m-by-n matrix as input, and returns a scalar result.

```
c = fun(x)
```

c is the output value for the center pixel in the m-by-n block x. nlfilter calls fun for each pixel in A. nlfilter zero pads the m-by-n block at the edges, if necessary.

B = nlfilter(A,[m n],fun,P1,P2,...) passes the additional parameters P1,P2,..., to fun.

B = nlfilter(A,'indexed',...) processes A as an indexed image, padding with ones if A is of class double and zeros if A is of class uint8.

Class Support

The input image, A, can be of any class supported by fun. The class of B depends on the class of the output from fun.

Remarks

nlfilter can take a long time to process large images. In some cases, the colfilt function can perform the same operation much faster.

Example

fun can be a function_handle, created using @. This example produces the same result as calling medfilt2 with a 3-by-3 neighborhood.

```
B = nlfilter(A,[3 3],@myfun);
```

where myfun is an M-file containing

function scalar = myfun(x)
scalar = median(x(:));

fun can also be an inline object. The example above can be written as

```
fun = inline('median(x(:))');
```

See Also

blkproc, colfilt

montage normxcorr2