nlfilter

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 the grayscale image A.

B = nlfilter(A,'indexed',___) processes A as an indexed image, padding with 0s if the class of A is uint8, uint16, or logical, and padding with 1s otherwise.

Note

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

Examples

Apply Median Filter to Image

This example shows how to apply a median filter to an image using nlfilter. This example produces the same result as calling medfilt2 with a 3-by-3 neighborhood.

Read an image into the workspace.

A = imread('cameraman.tif'); 

Convert the image to double.

A = im2double(A);

Create the function you want to apply to the image—a median filter.

fun = @(x) median(x(:));

Apply the filter to the image.

B = nlfilter(A,[3 3],fun); 

Display the original image and the filtered image, side-by-side.

montage({A,B})
title('Original Image (Left) and Median Filtered Image (Right)')

Input Arguments

A — Image to be filtered

numeric array

Image to be filtered, specified as a numeric array of any class supported by fun. When A is grayscale, it can be any numeric type or logical. When A is indexed, it can be logical, uint8, uint16, single, or double.

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

[m n] — Block size

2-element vector of positive integers

Block size, specified as a 2-element vector of positive integers. m is the number of rows and n is the number of columns in the block.

Example: B = nlfilter(A,[3 3],fun);

Data Types: single | double | logical

fun — Function handle

handle

Function handle specified as a handle. The function must accept an m-by-n matrix as input and return 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.

Data Types: function_handle

Output Arguments

B — Filtered image

numeric array

Filtered image, returned as numeric array. The class of B depends on the class of the output from fun.

Version History

Introduced before R2006a