matlab中wavedec2,说说wavedec2函数[通俗易懂]

wavedec2函数:

1.功能:实现图像(即二维信号)的多层分解.

多层,即多尺度.

2.格式:[c,s]=wavedec2(X,N,’wname’)

[c,s]=wavedec2(X,N,Lo_D,Hi_D)(我不讨论它)

3.参数说明:对图像X用wname小波基函数实现N层分解,

这里的小波基函数应该根据实际情况选择,具体选择办法可以搜之.输出为c,s.

c为各层分解系数,s为各层分解系数长度,也就是大小.

4.c的结构:c=[A(N)|H(N)|V(N)|D(N)|H(N-1)|V(N-1)|D(N-1)|H(N-2)|V(N-2)|D(N-2)|…|H(1)|V(1)|D(1)]

可见,c是一个行向量,即:1*(size(X)),(e.g,X=256*256,then c大小为:1*(256*256)=1*65536)

A(N)代表第N层低频系数,H(N)|V(N)|D(N)代表第N层高频系数,分别是水平,垂直,对角高频,以此类推,到H(1)|V(1)|D(1).

s的结构:是储存各层分解系数长度的,即第一行是A(N)的长度,第二行是H(N)|V(N)|D(N)|的长度,第三行是

H(N-1)|V(N-1)|D(N-1)的长度,倒数第二行是H(1)|V(1)|D(1)长度,最后一行是X的长度(大小)

另:MATLAB HELP 里面说得非常明白了,呵呵.

wavedec2

Multilevel 2-D wavelet decomposition Syntax [C,S] = wavedec2(X,N,’wname’)

[C,S] = wavedec2(X,N,Lo_D,Hi_D)

Description wavedec2 is a two-dimensional wavelet analysis function.

[C,S] = wavedec2(X,N,’wname’) returns the wavelet decomposition of the matrix X at level N, using the wavelet named in string ‘wname’ (see wfilters for more information).

Outputs are the decomposition vector C and the corresponding bookkeeping matrix S. N must be a strictly positive integer (see wmaxlev for more information).

Instead of giving the wavelet name, you can give the filters. For [C,S] = wavedec2(X,N,Lo_D,Hi_D), Lo_D is the decomposition low-pass filter and Hi_D is the decomposition high-pass filter.

Vector C is organized as C = [ A(N) | H(N) | V(N) | D(N) | … H(N-1) | V(N-1) | D(N-1) | … | H(1) | V(1) | D(1) ]. where A, H, V, D, are row vectors such that A = approximation coefficients H = horizontal detail coefficients V = vertical detail coefficients D = diagonal detail coefficients Each vector is the vector column-wise storage of a matrix.

Matrix S is such that S(1,:) = size of approximation coefficients(N) S(i,:) = size of detail coefficients(N-i+2) for i = 2, …N+1 and S(N+2,:) = size(X)

Examples% The current extension mode is zero-padding (see dwtmode).

% Load original image.

load woman;

% X contains the loaded image.

% Perform decomposition at level 2

% of X using db1.

[c,s] = wavedec2(X,2,’db1′);

% Decomposition structure organization.

sizex = size(X)

sizex =

256  256

sizec = size(c)

sizec =

1  65536

val_s = s

val_s =

64  64

64  64

128  128

256  256

Algorithm For images, an algorithm similar to the one-dimensional case is possible for two-dimensional wavelets and scaling functions obtained from one-dimensional ones by tensor product. This kind of two-dimensional DWT leads to a decomposition of approximation coefficients at level j in four components: the approximation at level j+1, and the details in three orientations (horizontal, vertical, and diagonal). The following chart describes the basic decomposition step for images:  So, for J=2, the two-dimensional wavelet tree has the form  See Alsodwt, waveinfo, waverec2, wfilters, wmaxlev ReferencesDaubechies, I. (1992), Ten lectures on wavelets, CBMS-NSF conference series in applied mathematics. SIAM Ed. Mallat, S. (1989), “A theory for multiresolution signal decomposition: the wavelet representation,” IEEE Pattern Anal. and Machine Intell., vol. 11, no. 7, pp. 674-693. Meyer, Y. (1990), Ondelettes et opérateurs, Tome 1, Hermann Ed. (English translation: Wavelets and operators, Cambridge Univ. Press. 1993.