integralBoxFilter
2-D box filtering of integral images
Syntax
Description
filters the integral image B
= integralBoxFilter(A
,filterSize
)A
with a 2-D box
filter with size specified by
filterSize
.
also specifies the normalization factor applied to the box
filter.B
= integralBoxFilter(___,"NormalizationFactor",normFactor
)
Examples
Filter Integral Image
Read image into the workspace.
A = imread('cameraman.tif');
Pad the image by the radius of the filter neighborhood. This example uses an 11-by-11 filter.
filterSize = [11 11]; padSize = (filterSize-1)/2; Apad = padarray(A, padSize, 'replicate','both');
Compute the integral image of the padded input image.
intA = integralImage(Apad);
Filter the integral image.
B = integralBoxFilter(intA, filterSize);
Display original image and filtered image.
figure
imshow(A)
title('Original Image')
figure
imshow(B,[])
title('Filtered Image')
Filter Image with Horizontal and Vertical Motion Blur
Read image into the workspace.
A = imread('cameraman.tif');
Pad the image by radius of the filter neighborhood, calculated (11-1)/2
.
padSize = [5 5]; Apad = padarray(A, padSize, 'replicate', 'both');
Calculate the integral image of the padded input.
intA = integralImage(Apad);
Filter the integral image with a vertical [11 1] filter.
Bvert = integralBoxFilter(intA, [11 1]);
Crop the output to retain input image size and display it.
Bvert = Bvert(:,6:end-5);
Filter the integral image with a horizontal [1 11] filter.
Bhorz = integralBoxFilter(intA, [1 11]);
Crop the output to retain input image size.
Bhorz = Bhorz(6:end-5,:);
Display the original image and the filtered images.
figure,
imshow(A)
title('Original Image')
figure,
imshow(Bvert,[])
title('Filtered with Vertical Filter')
figure,
imshow(Bhorz,[])
title('Filtered with Horizontal Filter')
Input Arguments
A
— Integral image to be filtered
numeric array
Integral image to be filtered, specified as a numeric array of any dimension.
The integral image must be upright —
integralBoxFilter
does not
support rotated integral images. The first row and
column of the integral image is assumed to be
zero-padded, as returned by integralImage
.
Data Types: double
filterSize
— Size of box filter
3
(default) | positive, odd integer | 2-element vector of positive, odd integers
Size of box filter, specified as a positive, odd integer or 2-element vector of positive, odd
integers. If filterSize
is
scalar, then integralBoxFilter
uses a square box filter.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
normFactor
— Normalization factor applied to box filter
numeric scalar
Normalization factor applied to the box filter, specified as a numeric scalar.
By default, the normalization factor has the value
1/filterSize.^2
when
filterSize
is a scalar, and
1/prod(filterSize)
when
filterSize
is a vector. The
default has the effect of a mean filter — the
pixels in the output image are the local means of
the image.
To get local area sums, set
normFactor
to
1
. To avoid overflow in such
circumstances, consider using double precision
images by converting the input image to data type
double
.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
Output Arguments
B
— Filtered image
numeric array
Filtered image, returned as a numeric array. integralBoxFilter
returns only
the parts of the filtering that are computed without
padding.
Data Types: double
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
integralBoxFilter
supports the generation of C code (requires MATLAB® Coder™). For more information, see Code Generation for Image Processing.The
normFactor
argument must be a compile-time constant.
GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.
Usage notes and limitations:
The
normFactor
argument must be a compile-time constant.
Version History
Introduced in R2015b
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