DCT digital watermarking

Hi Everyone,

I am working on a digital watemarking project. this is my first matlab project. So I really need help. I can embed and extract watermark from bmp or jpg. however because of that I do not change domain, watermarks are not robust in jpgs against compression.

I tried to get DCT block, then I quantized it, after that I tried to embed my watermark, at the end I tried to dequantize and inverseDCT. I could not successfully do it.

Can you please give a piece of code to show how can I do it

[Sean de Wolski]

Could you please give us a piece of code so we can see what you've done? Perhaps sample images to show the issues you're seeing as well.

[Halil]

code is here:

function z = DCT2(filename)
 image = imread(filename); % define your image
 [m,n, k] = size(image); % get size of your image
 
 imvector = reshape(image, m*n*k, 1); % reshape image
 zeros(imvector);
 imdct = dct(imvector); % compute DCT
 imagedct = reshape(imdct,m, n, k); % reshape result bacl
 
 %%embedding will be here
 imdct2 = reshape(imagedct, m*n*k, 1);
 imvector2 = idct(imdct2);
 image2 = reshape(imvector2, m,n,k);
 
figure(1)
imshow(image, [])
title('Original Image')
figure(2)
imshow(image2, [])
title('Image2')
 
end

What is the problem about codes. I want to embed watermark in the middle, but even without embbeding anythingimage2 is too corrupted.

[SHIREESHA THADKAPALLY]

are you using image watermark or text as watermark i mean u r embed text in image or image in image?

Answer 1

[Sean de Wolski]

Hi Halil,

The reason you're seeing the corrupted image is because you're working on all three channels (R,G,B) at once. These are three independent channels and thus need to be dealt with independently.

Here's your code modified to work with each channel independently. It doesn't actually do anything, but shows that the image will not be corrupted:

vec = @(x)reshape(x,numel(x),1);

image1 = imread('peppers.png'); % IPT sample image (don't call it image, MATLAB stock function)
[m,n,k] = size(image1); % get size of your image
image2 = zeros(m,n,k,class(image1)); %preallocate second image

for ii = 1:3;
  image2(:,:,ii) = reshape(idct(dct(vec(image1(:,:,ii)))),m,n);
  %vector of channel -> dct -> idct -> reshaped to original size
end

figure(1)
imshow(image1, [])
title('Original Image')

figure(2)
imshow(image2, [])
title('Image2')

Good Luck!

[Halil]

thanks

[Bhavneet Sharma]

while executing you code i got an error given below:

Error in dct (line 6)

image2(:,:,ii) = reshape(idct(dct(vec(image1(:,:,ii)))),m,n);

can you suggest me how to sove this error?

[Walter Roberson]

Please show the complete error message.

[Walter Roberson]

vec = @(x) double(x(:));

[Bhavneet Sharma]

Attempt to execute SCRIPT dct as a function:

C:\Users\Downloads\IMAGE WATERMARKING\DCT\dct.m

Error in dct (line 6)

image2(:,:,ii) = reshape(idct(dct(vec(image1(:,:,ii)))),m,n);

this is the complete error messgae.

[Walter Roberson]

You created a script named dct.m that attempts to call upon the MATLAB provided dct() function, but gets confused because its own name is also dct .

Rename your script to something else, such as try_dct.m

You will probably also need the change I give above to define vec .