Get 2D approximate wavelet coefficients

Hi, i need to get 2D approximate wavelet coefficients from an image. I've read all the documentation about but there is still one thing i can't understand. I do the following:

I get 2D coefficients and the bookeeping matrix:

[c,s]=wavedec2(image,2,'db4');
size(c)
s

ans =

             1       46153

s =

      61    52
      61    52
     115    97
     224   187

so, if i'm not wrong i'm getting 46153 wavelet coefficients on vector 'c' 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) ]

so i want to get A(N) which are approximate coefficients of level 2 but i don't know which is the de size of A(N) because of the first row of the bookeeping matrix (s) tells me that the size approximate coefficients of level 2 is a matrix of 61x52 according to what i get if i type:

coeffs=appcoef2(C,S,'db4',s);

but i don't understand completly that because according to the documentation the bookeeping matrix tells me that the number of coefficients should be:

62x51=3162 approximate coefficients of level 2

62x51=3162 detail coefficients of level 2

115x97=11155 detail coefficients of level 1

which makes a total of 17479 and not 46153.

Summarizing, i need approximate coefficients in a vector (not a matrix) and i'm not sure how doing this.

Any help or explanation would be great.

Thanks, David.

Answer 1

[Wayne King]

Hi, If you want the approximation coefficients at level 2

    load woman
    [C,S] = wavedec2(X,3,'db2');
    A2 = appcoef2(C,S,'db2',2);
    imagesc(A2);
    colormap gray;

Wayne

[David]

Hi, thanks for your answer Wayne.

That is the same i'm doing, but i need a vector with the coefficients not a matrix because i want to use it in a Support Vector Machine for classification.

Is not possible to obtain them from the vector 'c' given by wavedec2 command?

David.

Answer 2

[Tanaya]

Hey. i want to display detail coefficients of type double.