imboxfilt

2-D box filtering of images

Description

example

B = imboxfilt(A) filters image A with a 2-D, 3-by-3 box filter. A box filter is also called a mean filter.

example

B = imboxfilt(A,filterSize) filters image A with a 2-D box filter with size specified by filterSize.

example

B = imboxfilt(___,Name,Value) uses name-value pair arguments to control aspects of the filtering.

Examples

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Read image into the workspace.

A = imread('cameraman.tif');

Perform the mean filtering using an 11-by-11 filter.

localMean = imboxfilt(A,11);

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

imshowpair(A,localMean,'montage')

Read image into the workspace.

A = imread('cameraman.tif');

Change the data type of the image to double to avoid integer overflow.

A = double(A);

Filter image, calculating local area sums, using a 15-by-15 box filter. To calculate local area sums, rather than the mean, set the NormalizationFactor parameter to 1.

localSums = imboxfilt(A, 15, 'NormalizationFactor',1);

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

imshowpair(A,localSums,'montage')

Input Arguments

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Image to be filtered, specified as a numeric array of any dimension. If the input image has more than two dimensions (ndims(I)>2), such as for an RGB image, then imboxfilt performs box filtering of all 2-D planes along the higher dimensions.

If A contains Infs or NaNs, then the behavior of imboxfilt is undefined. This can happen when integral image based filtering is used. To restrict the propagation of Infs and NaNs in the output, consider using imfilter instead.

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

Size of box filter, specified as a positive odd integer or 2-element vector of positive, odd integers. If filterSize is scalar, then the box filter is square.

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

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: B = imboxfilt(A,5,'Padding','circular');

Padding pattern, specified as one of the following values or a numeric scalar. If you specify a scalar value, input image pixels outside the bounds of the image are implicitly assumed to have the scalar value.

ValueDescription
'circular'Input image values outside the bounds of the image are computed by implicitly assuming the input image is periodic.
'replicate'Input image values outside the bounds of the image are assumed equal to the nearest image border value.
'symmetric'Input image values outside the bounds of the image are computed by mirror-reflecting the array across the array border.

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

Normalization factor applied to box filter, specified as a numeric scalar.

The default 'NormalizationFactor' has the effect of a mean filter — the pixels in the output image are the local means of the image over the neighborhood determined by filterSize. To get local area sums, set 'NormalizationFactor' to 1. To avoid overflow in such circumstances, consider using double precision images by converting the input image to class double.

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

Output Arguments

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Filtered image, returned as a numeric array of the same size as the input image A.

Algorithms

imboxfilt performs filtering using either convolution-based filtering or integral image filtering, using an internal heuristic to determine which filtering approach to use.

Extended Capabilities

Introduced in R2015b