FSPECIAL

help fspecial

FSPECIAL Create predefined 2-D filters.
H = FSPECIAL(TYPE) creates a two-dimensional filter H of the
specified type. Possible values for TYPE are:

'average' averaging filter
'disk' circular averaging filter
'gaussian' Gaussian lowpass filter
'laplacian' filter approximating the 2-D Laplacian operator
'log' Laplacian of Gaussian filter
'motion' motion filter
'prewitt' Prewitt horizontal edge-emphasizing filter
'sobel' Sobel horizontal edge-emphasizing filter
'unsharp' unsharp contrast enhancement filter

Depending on TYPE, FSPECIAL may take additional parameters
which you can supply. These parameters all have default
values.

H = FSPECIAL('average',HSIZE) returns an averaging filter H of size
HSIZE. HSIZE can be a vector specifying the number of rows and columns in
H or a scalar, in which case H is a square matrix.
The default HSIZE is [3 3].

H = FSPECIAL('disk',RADIUS) returns a circular averaging filter
(pillbox) within the square matrix of side 2*RADIUS+1.
The default RADIUS is 5.

H = FSPECIAL('gaussian',HSIZE,SIGMA) returns a rotationally
symmetric Gaussian lowpass filter of size HSIZE with standard
deviation SIGMA (positive). HSIZE can be a vector specifying the
number of rows and columns in H or a scalar, in which case H is a
square matrix.
The default HSIZE is [3 3], the default SIGMA is 0.5.

H = FSPECIAL('laplacian',ALPHA) returns a 3-by-3 filter
approximating the shape of the two-dimensional Laplacian
operator. The parameter ALPHA controls the shape of the
Laplacian and must be in the range 0.0 to 1.0.
The default ALPHA is 0.2.

H = FSPECIAL('log',HSIZE,SIGMA) returns a rotationally symmetric
Laplacian of Gaussian filter of size HSIZE with standard deviation
SIGMA (positive). HSIZE can be a vector specifying the number of rows
and columns in H or a scalar, in which case H is a square matrix.
The default HSIZE is [5 5], the default SIGMA is 0.5.

H = FSPECIAL('motion',LEN,THETA) returns a filter to approximate, once
convolved with an image, the linear motion of a camera by LEN pixels,
with an angle of THETA degrees in a counter-clockwise direction. The
filter becomes a vector for horizontal and vertical motions. The
default LEN is 9, the default THETA is 0, which corresponds to a
horizontal motion of 9 pixels.

H = FSPECIAL('prewitt') returns 3-by-3 filter that emphasizes
horizontal edges by approximating a vertical gradient. If you need to
emphasize vertical edges, transpose the filter H: H'.

[1 1 1;0 0 0;-1 -1 -1].

H = FSPECIAL('sobel') returns 3-by-3 filter that emphasizes
horizontal edges utilizing the smoothing effect by approximating a
vertical gradient. If you need to emphasize vertical edges, transpose
the filter H: H'.

[1 2 1;0 0 0;-1 -2 -1].

H = FSPECIAL('unsharp',ALPHA) returns a 3-by-3 unsharp contrast
enhancement filter. FSPECIAL creates the unsharp filter from the
negative of the Laplacian filter with parameter ALPHA. ALPHA controls
the shape of the Laplacian and must be in the range 0.0 to 1.0.
The default ALPHA is 0.2.

Class Support
-------------
H is of class double.

Example
-------
I = imread('cameraman.tif');
subplot(2,2,1);imshow(I);title('Original Image');
H = fspecial('motion',20,45);
MotionBlur = imfilter(I,H,'replicate');
subplot(2,2,2);imshow(MotionBlur);title('Motion Blurred Image');
H = fspecial('disk',10);
blurred = imfilter(I,H,'replicate');
subplot(2,2,3);imshow(blurred);title('Blurred Image');
H = fspecial('unsharp');
sharpened = imfilter(I,H,'replicate');
subplot(2,2,4);imshow(sharpened);title('Sharpened Image');

See also conv2, edge, filter2, fsamp2, fwind1, fwind2, imfilter.

Reference page in Help browser
doc fspecial