how to apply dwt and inverse dwt for an image

hi all..im writing a code for getting an image and perform dwt for one level to get 4 sub bands and apply inverse dwt to reconstruct the image. The LL band should contain the intensity imformation of the image but for me the figure for LL is plain white and when tried for reconstructing image iam getting same white screen image. i am not sure what was the mistake i have done.. the code i have written is shown below,

clear all;
close all;
i=imread('image22.jpg');
sX=size(i);
[LL,LH,HL,HH]=dwt2(i,'db1');
figure(1)
subplot(2,2,1);imshow(LL);title('LL band of image');
subplot(2,2,2);imshow(LH);title('LH band of image');
subplot(2,2,3);imshow(HL);title('HL band of image');
subplot(2,2,4);imshow(HH);title('HH band of image');
X = idwt2(LL,LH,HL,HH,'db1',sX);
figure(2)
imshow(X);

kindly help me to fix the same.

[Arnab Banerjee]

Sir, would you please send me the code mention above, but in 3 level, at [e-mail]

[YEPDIA LEE]

please sir,can you Dme the code mentionned above on decomposition and reconstruction of an image with 2D wavelet transform! you can send it at [e-mail] tanks.

[Kaviarasi Ezhumalai]

send me the correct code for the above code u have mentioned .

send it at [e-mail]

[omer hussain]

Dear Dr.,

I am a scholar and i am trying to implement a paper and i stuck in implementing the 3 Level DWT of an grayscale image.

I will be very thankful to you if you can send me the code at [e-mail]

[mariena aloor]

Hai Sir

I want to take the features from blood smear image.So how i will use discrete wavelet transform for feature extraction.

I want the code for second level dwt only for the LL band.Kindly give me the matlab code for feature extraction using discrete wavelet transform my mail id is : [e-mail]

[Walter Roberson]

mariena aloor, please read http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

Answer 1

[Nawin K Sharma]

dwt2 results are in double (Integer) format. For double format, imshow treats non zero values as White and Zero values as Black. That's why you are getting full white screen.

Try this modification in your code

LL=uint8(LL);

uint8 converts double to unsigned integer of 8 bit format,which is used in gray scale or colored images.

If you want o retain double format, use this

imshow(uint8(LL))

[munipraveena rela]

yes, it is working . thank you

[anuja dixit]

Thank you so much. It's working.

[Nitish Chandra]

Error in dw (line 6)

[LL,LH,HL,HH]=dwt2(i,'db1');

showing this error.

what i have to do??

send me the right code on [e-mail]

[Walter Roberson]

What is the complete error message?

[Sangeetha Kumar]

Sir please kindly send the 3 level DWT for grey scale image [e-mail]

[lavanya valli]

sir plz send me the 2 level DWT for grey scale image [e-mail]

[Toon Tiam]

Had the same issues and your solution solveed it! Thank you!

Answer 2

[chaitanya goteti]

Use uint8 while displaying the bands, like imshow(uint8(LL)). Hope this helps

[Afeza Ajirah]

i tried this and it appears like this

Answer 3

[umme kulsum]

You can use imagesc instead of imshow command

Answer 4

[Wayne King]

Are you sure it is just not the scaling of the image in imshow() that is causing you problems?

For example, note:

    load woman;
    sX = size(X);
    [LL,LH,HL,HH]=dwt2(X,'db1');
    Xrec = idwt2(LL,LH,HL,HH,'db1',sX);
    max(max(abs(X-Xrec)))

The above shows perfect reconstruction. The maximum absolute value of the difference between elements in the original matrix and the reconstructed matrix is on the order of 10^{-13}

[Sathish Kumar]

'imshow' is to display the image...i dont think is might be a problem..because imshow of original image will display the input original image perfectly..

[Wayne King]

I understand what imshow() is used for, but did you verify that you get perfect reconstruction with your image?

Can you attach your image?

[shaghayegh alijanian]

i get this error would you please help me? Error using - Integers can only be combined with integers of the same class, or scalar doubles.

Error in jpg4 (line 9) max(max(abs(X) - abs(Xrec)))

[Walter Roberson]

max(max(double(abs(X)) - double(abs(Xrec))))

Answer 5

[Karbala'a Unvi. Science]

Hi every one,... I worked on your code and I did some modification on it and I made it work because I have the same project on my PHD project so if you want the modified code I can send it to you when you send me your e-mail. and give me your opinion. yours Zeyad

[lavanya valli]

sir plz send me the code [e-mail]

[Tapaswini Hansdah]

sir can you send me aswell ? [e-mail]

[Madhu Oruganti]

Dear sir, I am also working for my phD course can you please share the code at [e-mail]

Answer 6

[Sam]

At the end of the program just modify it as "imshow(X,[])", and it will work.

[Afeza Ajirah]

I tried it, but it still display plain white. Hmm, anyone can help?

Answer 7

[Ahmad Shaheen]

After i=imread('image22.jpg'); insert the following: i=im2double(i); and it will works.

Answer 8

[Harmeet Kaur]

hello everyone the above code is not giving the reconstructed image. the output of reconstruction is as follows:

[Walter Roberson]

Which above code?

[Fatima Munvar]

the following code not giving reconstructed image pls help me with this

close all;
clear all;
X=imread('Lilly_Closeup.bmp');
imshow(X);
i=imresize(X,[512 512]);
figure(1);
imshow(i);
sX=size(X);
[LL,LH,HL,HH]= dwt2(X,'db1');
figure(2)
subplot(2,2,1);imshow(LL);title('LL band of image');
subplot(2,2,2);imshow(LH);title('LH band of image');
subplot(2,2,3);imshow(HL);title('HL band of image');
subplot(2,2,4);imshow(HH);title('HH band of image');
 Xrec=idwt2(LL,LH,HL,HH,'db1',sX);
% sx=size(X)
% A1=idwt2(LL,[],[],[],'db1',sX);
% H1=idwt2([],LH,[],[],'db1',sX);
% V1=idwt2(LL,[],HL,[],'db1',sX);
% D1=idwt2(LL,[],[],HH,'db1',sX);
 max(max(abs(i-Xrec)));
figure(3);
imshow(Xrec);

I am getting error as below

Error using  - 
Integers can only be combined with integers of the same class, or scalar doubles.

Error in dwt21 (line 21)
 max(max(abs(i-Xrec)));

[Walter Roberson]

The line

   max(max(abs(i-Xrec)));

tries to calculate something abut then it throws away the results of the calculation. The easiest repair is to comment out the line.

[Karbala'a Unvi. Science]

Dear Sir,

Try this code and tell me is it working ornot..

clc, close all;
clear all;
X=imread('3.bmp');
imshow(X);
X= double(X);
i=imresize(X,[512 512]);
figure(1);
imshow(i);
sX=size(X);
[LL,LH,HL,HH]= dwt2(X,'db1');
figure(2)
subplot(2,2,1);imshow(LL);title('LL band of image');
subplot(2,2,2);imshow(LH);title('LH band of image');
subplot(2,2,3);imshow(HL);title('HL band of image');
subplot(2,2,4);imshow(HH);title('HH band of image');
%%
 Xrec=idwt2(LL,LH,HL,HH,'db1',sX);
% sx=size(X)
% A1=idwt2(LL,[],[],[],'db1',sX);
% H1=idwt2([],LH,[],[],'db1',sX);
% V1=idwt2(LL,[],HL,[],'db1',sX);
% D1=idwt2(LL,[],[],HH,'db1',sX);
 max(max(abs(X-Xrec)))
figure(3);
imshow(uint8(Xrec));

Answer 9

[Ankita Bansal]

Hi Fatima, in your code the sizes of X and i are not equal and you are using X as an input to dwt function. Hence whatever calculation will be done after [LL, LH, HL, HH] = dwt2(X,'db1'); will use X. So, when you try to calculate inverse dwt, the data you will get will be of same size as that of X. Also, the datatype of output of idwt is double whereas i is of uint8 datatype. So, the first reason of getting error is different data type and the second reason is size. To check whether the output you are getting is correct or not you can write max(max(abs(X-uint8(Xrec)))) instead of max(max(abs(i-Xrec))).

if true
  % code
end 
close all; 
clear all; 
X=imread('image.png'); 
imshow(X); 
i=imresize(X,[512 512]); 
figure; 
imshow(i); 
sX=size(X); 
[LL,LH,HL,HH]= dwt2(X,'db1'); 
Figure; 
subplot(2,2,1);imshow(LL);title('LL band of image'); 
subplot(2,2,2);imshow(LH);title('LH band of image'); 
subplot(2,2,3);imshow(HL);title('HL band of image'); 
subplot(2,2,4);imshow(HH);title('HH band of image'); 
Xrec=idwt2(LL,LH,HL,HH,'db1',sX); 
max(max(abs(X-uint8(Xrec)))); 
figure;
imshow(Xrec);

Hope this helps

[Rahul Kumar Singh]

 max(max(abs(X-uint8(Xrec))));

having problem with this still the reconstructed image is turning out to be white kindly help!

[Walter Roberson]

 imshow(uint8(Xrec))

[Rahul Kumar Singh]

yeah its working now thanks!

[Rahul Kumar Singh]

hello, i am currently working on image steganography in transform domain. As i am new to this i only the theoritical part . my question is after getting the subbands LL,LH,HL,HH how do we obtain the wavelet coeffients so that we can divide them into blocks of four and then choose m\2 blocks out of it(where m is the length of the secret message(in bits) to be embedded ) so that 2 bits can be embedded in each block by pattern matrix method.

i hope you understood my question. any suggestion will help.

[Karbala'a Unvi. Science]

try this one

clc, close all;
clear all;
X=imread('3.bmp');
imshow(X);
X= double(X);
i=imresize(X,[512 512]);
figure(1);
imshow(i);
sX=size(X);
[LL,LH,HL,HH]= dwt2(X,'db1');
figure(2)
subplot(2,2,1);imshow(LL);title('LL band of image');
subplot(2,2,2);imshow(LH);title('LH band of image');
subplot(2,2,3);imshow(HL);title('HL band of image');
subplot(2,2,4);imshow(HH);title('HH band of image');
%%
 Xrec=idwt2(LL,LH,HL,HH,'db1',sX);
% sx=size(X)
% A1=idwt2(LL,[],[],[],'db1',sX);
% H1=idwt2([],LH,[],[],'db1',sX);
% V1=idwt2(LL,[],HL,[],'db1',sX);
% D1=idwt2(LL,[],[],HH,'db1',sX);
 max(max(abs(X-Xrec)))
figure(3);
imshow(uint8(Xrec));

Answer 10

[pallavi singh]

SIr,

Can u tell me the code of dwt ?

[Walter Roberson]

At the MATLAB command prompt, command

type dwt

[pallavi singh]

how can apply dwt & idwt in an image

[Walter Roberson]

You have a small number of choices:

1. You can apply dwt for every row (of every color plane) independently;
2. You can apply dwt for every column (of every color plane) independently;
3. You can apply dwt for every row (of every color plane) independently, and transpose the result and apply dwt to every row (of every color plane) of the result. This is similar to the way that fft2() is fft(fft(IMAGE).')
4. You can apply dwt for every column (of every color plane) independently, and transpose the result and apply dwt to every column (of every color plane) of the result. This is similar to the way that fft2() is fft(fft(IMAGE).'). In theory this should give the same result as #3
5. You can reshape the image into a single continuous row and apply dwt to that
6. You can reshape the image into a single continuous column and apply dwt to that

To be clear: dwt can only be used on one vector at a time, so you cannot just apply it to a 2D or 3D (RGB) array.

See also: dwt2()

[pallavi singh]

Sir , can u tell me the code of 2D-DWT?