fspecial()函数解析

今天来总结一下fspecial()函数用法：
h = fspecial(type)
h = fspecial(type，para)
h = fspecial(type, pare, sigma)
其中type指定算子的类型，pare指定相应的参数，sigmasigma表示滤波器的标准差，单位为像素，默认值为0.5。

1、’average’
为均值滤波，参数为hsize代表模板尺寸，默认值为【3，3】。
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].

2、’gaussian’
为高斯低通滤波，有两个参数，hsize表示模板尺寸，默认值为【3 3】，sigma为滤波器的标准值，单位为像素，默认值为0.5.
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.

3、’laplacian’
为拉普拉斯算子，参数alpha用于控制算子形状，取值范围为【0，1】，默认值为0.2.

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.

4、’log’
为拉普拉斯高斯算子，有两个参数，hsize表示模板尺寸，默认值为【3 3】，sigma为滤波器的标准差，单位为像素，默认值为0.5.
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.

5、’prewitt’
用于边缘增强，大小为【3 3】，无参数
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].

6、’sobel’
用于边缘提取，无参数
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].

7、’unsharp’
为对比度增强滤波器。参数alpha用于控制滤波器的形状，范围为【0，1】，默认值为0.2.
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.

8、’motion’
为运动模糊算子，有两个参数，表示摄像物体逆时针方向以theta角度运动了len个像素，len的默认值为9，theta的默认值为0；
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.

9、’disk’
为圆形区域均值滤波，参数为radius代表区域半径，默认值为5.
H = FSPECIAL(‘disk’,RADIUS) returns a circular averaging filter

(pillbox) within the square matrix of side 2*RADIUS+1.

The default RADIUS is 5.