Image Processing Toolbox

imfilter

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.

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

Examples

This example starts by reading an image of a bouquet of flowers into a three-dimensional array of uint8 values, called rgb. The imshow function displays the original image, entitled 'Original'.

• rgb = imread('flowers.tif');
  imshow(rgb), title('Original')
  

Create a filter, h, that can be used to approximate linear camera motion. Use imfilter on the three-dimensional RGB image, rgb, to create a new image, rgb2.

• h = fspecial('motion', 50, 45);
  rgb2 = imfilter(rgb, h);
  figure, imshow(rgb2), title('Filtered')
  

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
  
    rgb2     362x500x3       543000  uint8 array
  

Filter the image once more, this time specifying the replicate boundary option and observe that the picture now extends to the border.

• rgb3 = imfilter(rgb, h, 'replicate');
  figure, imshow(rgb3), title('Filtered with boundary replication')
  

See Also

conv2, convn, filter2

imfill

imfinfo