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Extract 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.
appcoef2 computes the approximation coefficients of a two-dimensional signal.
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.
Instead of giving the wavelet name, you can give the filters.
For 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).
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.
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