imfilter (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Multidimensional image filtering

Syntax

B = imfilter(A,H)
B = imfilter(A,H,option1,option2,...)

Description

B = imfilter(A,H) filters the multidimensional array A with the multidimensional filter H. The array A can be a nonsparse numeric array of any class and dimension. The result B has the same size and class as A.

Each element of the output B is computed using double-precision floating point. If A is an integer array, then output elements that exceed the range of the integer type are truncated, and fractional values are rounded.

B = imfilter(A,H,option1,option2,...) performs multidimensional filtering according to the specified options. Option arguments can have the following values.

Boundary Options
Option
Description

X
Input array values outside the bounds of the array are implicitly assumed to have the value X. When no boundary option is specified, imfilter uses X = 0.

'symmetric'
Input array values outside the bounds of the array are computed by mirror-reflecting the array across the array border.

'replicate'
Input array values outside the bounds of the array are assumed to equal the nearest array border value.

'circular'
Input array values outside the bounds of the array are computed by implicitly assuming the input array is periodic.

Output Size Options
Option
Description

'same'
The output array is the same size as the input array. This is the default behavior when no output size options are specified.

'full'
The output array is the full filtered result, and so is larger than the input array.

Correlation and Convolution Options
Option
Description

'corr'
imfilter performs multidimensional filtering using correlation, which is the same way that filter2 performs filtering. When no correlation or convolution option is specified, imfilter uses correlation.

'conv'
imfilter performs multidimensional filtering using convolution.

**Boundary Options**
Option	Description
`X`	Input array values outside the bounds of the array are implicitly assumed to have the value `X`. When no boundary option is specified, `imfilter` uses `X = 0`.
`'symmetric'`	Input array values outside the bounds of the array are computed by mirror-reflecting the array across the array border.
`'replicate'`	Input array values outside the bounds of the array are assumed to equal the nearest array border value.
`'circular'`	Input array values outside the bounds of the array are computed by implicitly assuming the input array is periodic.

**Output Size Options**
Option	Description
`'same'`	The output array is the same size as the input array. This is the default behavior when no output size options are specified.
`'full'`	The output array is the full filtered result, and so is larger than the input array.

**Correlation and Convolution Options**
Option	Description
`'corr'`	`imfilter` performs multidimensional filtering using correlation, which is the same way that `filter2` performs filtering. When no correlation or convolution option is specified, `imfilter` uses correlation.
`'conv'`	`imfilter` performs multidimensional filtering using convolution.

N-D convolution is related to N-D correlation by a reflection of the filter matrix.

Note On Intel architecture processors, imfilter can take advantage of the Intel Performance Primitives Library (IPPL), thus accelerating its execution time. IPPL is activated only if A and H are both two-dimensional and A is of class uint8, int16, or single.

Examples

Read a color image into the workspace and view it.

originalRGB = imread('peppers.png');
imshow(originalRGB)

Create a filter, h, that can be used to approximate linear camera motion.

```
h = fspecial('motion', 50, 45);
```

Apply the filter, using imfilter, to the image rgb to create a new image, rgb2.

filteredRGB = imfilter(originalRGB, h);
figure, imshow(filteredRGB)

Note that imfilter is more memory efficient than some other filtering operations in that it outputs an array of the same data type as the input image array. In this example, the output is an array of uint8.

whos rgb2
  Name       Size                   Bytes  Class

  h         37x37                   10952  double array
  rgb      384x512x3               589824  uint8 array
  rgb2     384x512x3               589824  uint8 array

This example specifies the replicate boundary option.

boundaryReplicateRGB = imfilter(originalRGB, h, 'replicate');
figure, imshow(boundaryReplicateRGB)

See Also

conv2, convn, filter2, fspecial, ippl

imfill imfinfo