2-D approximation coefficients
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)
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).
% 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
The algorithm is built on the same principle as appcoef.