When displaying wavelet transform, low pass image cA2 doesn't appear. No significant difference when using im2double in spite of double.Here below is my code:
% Read pgm file and normalize it by hitogram equalization
J = imread('C:\baboon.pgm');
J = histeq(J);
figure;imshow(J);
% Decompose and display wavelet transform result
dwtmode('per', 'nodisp');
I1 = double(J); % I1 = im2double(J);
[C,S] = wavedec2(I1, 2, 'db1');
ii = 1; jj = prod(S(1,:));
cA2 = reshape(C(ii:jj),S(1,:));
ii = jj+1; jj = ii + prod(S(2,:)) - 1;
cH2 = reshape(C(ii:jj),S(2,:));
ii = jj+1; jj = ii + prod(S(2,:)) - 1;
cV2 = reshape(C(ii:jj),S(2,:));
ii = jj+1; jj = ii + prod(S(2,:)) - 1;
cD2 = reshape(C(ii:jj),S(2,:));
ii = jj+1; jj = ii + prod(S(3,:)) - 1;
cH1 = reshape(C(ii:jj),S(3,:));
ii = jj+1; jj = ii + prod(S(3,:)) - 1;
cV1 = reshape(C(ii:jj),S(3,:));
ii = jj+1; jj = ii + prod(S(3,:)) - 1;
cD1 = reshape(C(ii:jj),S(3,:));
figure;imshow([[cA2,cH2; cV2,cD2],cH1;cV1,cD1]);