appcoef2 :: Functions (Wavelet Toolbox™)

appcoef2

Purpose

2-D approximation coefficients

Syntax

A = appcoef2(C,S,'wname',N)
A = appcoef2(C,S,'wname')
A = appcoef2(C,S,Lo_R,Hi_R)
A = appcoef2(C,S,Lo_R,Hi_R,N)

Description

appcoef2 is a two-dimensional wavelet analysis function. It computes the approximation coefficients of a two-dimensional signal. The syntaxes allow you to give the wavelet name or the filters as inputs.

A = appcoef2(C,S,'wname',N) computes the approximation coefficients at level N using the wavelet decomposition structure [C,S] (see wavedec2 for more information).

'wname' is a string containing the wavelet name. Level N must be an integer such that 0 N size(S,1)-2.

A = appcoef2(C,S,'wname') extracts the approximation coefficients at the last level: size(S,1)-2.

A = appcoef2(C,S,Lo_R,Hi_R) or A = appcoef2(C,S,Lo_R,Hi_R,N), Lo_R is the reconstruction low-pass filter and Hi_R is the reconstruction high-pass filter (see wfilters for more information).

Remarks

If C and S are obtained from an indexed image analysis or a truecolor image analysis, A is an m-by-n matrix or an m-by-n-by-3 array, respectively.

For more information on image formats, see the image and imfinfo reference pages.

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'); 
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

% Extract approximation coefficients 
% at level 2. 
ca2 = appcoef2(c,s,'db1',2); 
sizeca2 = size(ca2)

sizeca2 =
    64     64

% Compute approximation coefficients 
% at level 1. 
ca1 = appcoef2(c,s,'db1',1); 
sizeca1 = size(ca1)

sizeca1 =
   128    128

Algorithm

The algorithm is built on the same principle as appcoef.