nlfilter (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Perform general sliding-neighborhood operations

Syntax

B = nlfilter(A,[m n],fun)
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)
```

fun must be a function handle.

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,'indexed',...) processes A as an indexed image, padding with 1's if A is of class double and 0's 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

This example produces the same result as calling medfilt2 with a 3-by-3 neighborhood.

A = imread('cameraman.tif');
fun = @(x) median(x(:));
B = nlfilter(A,[3 3],fun);
imshow(A), figure, imshow(B)

See Also

blkproc, colfilt, function_handle

montage normxcorr2