MATLAB: Need help in dwt2 ….

MATLAB

I had written this code to perform dwt2 on my image:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clc;
clear all;
X=double(imread('Lena.bmp'));
X=fix(X);
[LL1,HL1,LH1,HH1]=dwt2(X,'bior1.1');
[LL2,HL2,LH2,HH2]=dwt2(LL1,'bior1.1');
[LL3,HL3,LH3,HH3]=dwt2(LL2,'bior1.1');
Y=[[[LL3,HL3;LH3,HH3],HL2;LH2,HH2],HL1;LH1,HH1]; 
Y=fix(Y);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

but it doesn't worked with me when I tried filter ('bior4.4') which I needed in my work help me plz…and thank you in advance..

note:

the error appears in the following lines:

[LL1,HL1,LH1,HH1]=dwt2(X,'bior4.4');

and

Y=[[[LL3,HL3;LH3,HH3],HL2;LH2,HH2],HL1;LH1,HH1];

Best Answer

Hi, I think you are better off to use wavedec2 instead of iterating on the LL output with dwt2(). wavedec2() does that anyway.

load woman;
[C,S] = wavedec2(X,3,'bior4.4');

Then if you want to extract the details, detcoef2(), and appcoef2()

Or waverec2() to reconstruct projections.

If you really have some reason for iterating with dwt2(), please show the error you get.

Wayne

Related Solutions

MATLAB: What is the difference between “dwt2()” and “wavedec2()”

Basically dwt2() applies 2-D discreet wavelet transformation on the image and provides the approximation and detail coefficients matrices directly. Whereas, wavedec2() only provides the wavelet decomposition vector and the bookkeeping matrix, which contains the number of coefficients by level and orientation. And you can to get approximation and detail coefficients matrices from the wavelet decomposition vector and the bookkeeping matrix using the detcoef2() and appcoef2() function.

Exact same approximation and detail coefficients matrices can be generated using any of those (dwt2 or wavedec2) functions. See the example below

close all; clc;
% Decomposition using wavedec2 and appcoef2
load woman;
[c, s] = wavedec2(X, 1, 'db1');
A1 = appcoef2(c, s, 'db1', 1);
figure; imshow(A1, []); title('Using wavedec2 and appcoef2');
% Decomposition using dwt2
load woman;
[A2, ~, ~, ~] = dwt2(X, 'db1');
figure; imshow(A2, []); title('Using dwt2');
% Difference image between A1 and A2
diffImage = imabsdiff(A1, A2);
figure; imshow(diffImage, []); title('Difference Image');

Now, here is an example how you can display different sub-bands at different wavelet decomposition levels.

clc; close all;
load woman;
[c, s] = wavedec2(X, 3, 'haar');
% Extract the level 1 approximation and detail coefficients.
[H1, V1, D1] = detcoef2('all', c, s, 1);
A1 = appcoef2(c, s, 'haar', 1);
% Display images


figure; subplot(2, 2, 1); imshow(A1, []); title('Approximation Coef. of Level 1');
subplot(2, 2, 2); imshow(H1, []); title('Horizontal Detail Coef. of Level 1');
subplot(2, 2, 3); imshow(V1, []); title('Vertical Detail Coef. of Level 1');
subplot(2, 2, 4); imshow(D1, []); title('Diagonal Detail Coef. of Level 1');
% Extract the level 2 approximation and detail coefficients.
[H2, V2, D2] = detcoef2('all', c, s, 2);
A2 = appcoef2(c, s, 'haar', 2);
% Display images
figure; subplot(2, 2, 1); imshow(A2, []); title('Approximation Coef. of Level 2');
subplot(2, 2, 2); imshow(H2, []); title('Horizontal Detail Coef. of Level 2');
subplot(2, 2, 3); imshow(V2, []); title('Vertical Detail Coef. of Level 2');
subplot(2, 2, 4); imshow(D2, []); title('Diagonal Detail Coef. of Level 2');
% Extract the level 3 approximation and detail coefficients.
[H3, V3, D3] = detcoef2('all', c, s, 3);
A3 = appcoef2(c, s, 'haar', 3);
% Display images
figure; subplot(2, 2, 1); imshow(A3, []); title('Approximation Coef. of Level 3');
subplot(2, 2, 2); imshow(H3, []); title('Horizontal Detail Coef. of Level 3');
subplot(2, 2, 3); imshow(V3, []); title('Vertical Detail Coef. of Level 3');
subplot(2, 2, 4); imshow(D3, []); title('Diagonal Detail Coef. of Level 3');

Hope this helps!

MATLAB: How to perform 2 level dwt without using dwt2 wavelet

Use wavedec2() that allows you to specify the level.

Best Answer

Related Solutions

MATLAB: What is the difference between “dwt2()” and “wavedec2()”

MATLAB: How to perform 2 level dwt without using dwt2 wavelet

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