fspecial函式
用於建立預定義的濾波運算元，其語法格式為：
h = fspecial(type)
h = fspecial(type，para)
其中type指定運算元的類型，para指定相應的參數；
type的類型有
'average'
averaging filter
為均值濾波，參數為hsize代表模板尺寸，默認值為[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].
'disk'
circular averaging filter
為圓形區域均值濾波，參數為radius代表區域半徑，默認值為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.
'gaussian'
Gaussian lowpass filter
為高斯低通濾波，有兩個參數，hsize表示模板尺寸，默認值為[3 3]，sigma為濾波器的標準差，單位為像素，默認值為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.
'laplacian'
filter approximating the 2-D Laplacian operator
為拉普拉斯運算元，參數alpha用於控制運算元形狀，取值範圍為[0，1]，默認值為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.
'log'
Laplacian of Gaussian filter
為拉普拉斯高斯運算元，有兩個參數，hsize表示模板尺寸，默認值為[3 3]，sigma為濾波器的標準差，單位為像素，默認值為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.
'motion'
motion filter
為運動模糊運算元，有兩個參數，表示攝像物體逆時針方向以theta角度運動了len個像素，len的默認值為9，theta的默認值為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.
'prewitt'
Prewitt horizontal edge-emphasizing filter
用於邊緣增強，大小為[3 3]，無參數
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].
'sobel'
Sobel horizontal edge-emphasizing filter
用於邊緣提取，無參數
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].
'unsharp'
unsharp contrast enhancement filter
為對比度增強濾波器。參數alpha用於控制濾波器的形狀，範圍為[0，1]，默認值為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.
