This is a dct code on watermark embedding. Please fix it

The error I'm encountering is this -->

Warning: Size vector should be a row vector with integer elements.
> In watermarkemb at 27
??? Index exceeds matrix dimensions.

Error in ==> watermarkemb at 36
    dct_block=dct2(cover_object(x:x+blocksize-1,y:y+blocksize-1));

This is the code -->

clc;
clear all;

start_time=cputime;

k=50;
blocksize=8;

file_name='scene.jpg';
cover_object=double(rgb2gray(imread(file_name)));

Mc=size(cover_object,1);       
Nc=size(cover_object,2);          

max_message=Mc*Nc/(blocksize^2);

file_name='fishy.jpg';
message=double(rgb2gray(imread(file_name)));
Mm=size(message,1);      
Nm=size(message,2);                  
message=round(reshape(message,Mm*Nm,1)./256);

if (length(message) > max_message)
    error('Message too large to fit in Cover Object')
end

message_pad=ones(1,max_message);
message_pad(1:length(message))=message;

watermarked_image_r=cover_object;

x=1;
y=1;
for (kk = 1:length(message_pad))

      dct_block=dct2(cover_object(y:y+blocksize-1,x:x+blocksize-1));

      if (message_pad(kk) == 0)

          if (dct_block(5,2) < dct_block(4,3))
                  temp=dct_block(4,3);
                  dct_block(4,3)=dct_block(5,2);
                  dct_block(5,2)=temp;
          end

      elseif (message_pad(kk) == 1)

          if (dct_block(5,2) >= dct_block(4,3))
                  temp=dct_block(4,3);
                  dct_block(4,3)=dct_block(5,2);
                  dct_block(5,2)=temp;
          end
      end

      if dct_block(5,2) > dct_block(4,3)
          if dct_block(5,2) - dct_block(4,3) < k
              dct_block(5,2)=dct_block(5,2)+(k/2);
              dct_block(4,3)=dct_block(4,3)-(k/2);            
          end
      else  
           if dct_block(4,3) - dct_block(5,2) < k
              dct_block(4,3)=dct_block(4,3)+(k/2);  
              dct_block(5,2)=dct_block(5,2)-(k/2);
          end
      end

      watermarked_image(y:y+blocksize-1,x:x+blocksize-1)=idct2(dct_block);    

      if (x+blocksize) >= Nc
          x=1;
          y=y+blocksize;
      else
          x=x+blocksize;
      end
  end

watermarked_image_int=uint8(watermarked_image);
imwrite(watermarked_image_int,'dct1_watermarked_circuit.jpg','jpg');

elapsed_time=cputime-start_time,

subplot(211);imshow(cover_object,[]);title('Original Image')
subplot(212);imshow(watermarked_image,[]);title('Watermarked Image')

Answer 1

[Walter Roberson]

Put in a breakpoint and check the value of max_message

[Lester]

I tweaked the max_message. Now the output is getting cropped.

[Walter Roberson]

What did you tweak it to?

Did you resolve the problem with index out of range?

[Lester]

I have no clue how to do with the index problem sir. I tweaked it to this -->

Mc=size(cover_object,1); Nc=size(cover_object,1);

max_message= Mc*Nc/(blocksize^2);

[Walter Roberson]

Leave Nc=size(cover_object,2); like you had before, but use

max_message = floor(Mc/blocksize) * floor(Nc/blocksize);

This will also help correct your problem with index out of range.

[Lester]

Thanks a lot sir. It worked. The watermark is invisible. How to make it visible? Is it possible to get the output image in colored format?

[Walter Roberson]

Instead of converting to grayscale, you can embed the watermark into one of the color planes, and then put the color planes back together.

[Lester]

Any idea to have a slightly visible watermark sir? As you know the watermark is invisible in our case.

[Walter Roberson]

No idea. I do not look at the code about how the watermark is calculated or embedded.

[Lester]

Sir we have done the changes that you had suggested about color planes but what changes should we do in the watermark extraction code so that we get the colored output.

   clc;
   clear all;

   start_time=cputime;

   blocksize=8;    

   file_name='dct1_watermarked_circuit.jpg';
   watermarked_image=double(imread(file_name));

   Mw=size(watermarked_image,1);
   Nw=size(watermarked_image,2);

   max_message=Mw*Nw/(blocksize^2);

   file_name='lena.jpg';
   orig_watermark=double(rgb2gray(imread(file_name)));

   Mo=size(orig_watermark,1);
   No=size(orig_watermark,2);

   x=1;
   y=1;
   for (kk = 1:max_message)

      dct_block=dct2(watermarked_image(y:y+blocksize-1,x:x+blocksize-1));

      if dct_block(5,2) > dct_block(4,3)
          message_vector(kk)=0;
      else
          message_vector(kk)=1;
      end

      if (x+blocksize) >= Nw
          x=1;
          y=y+blocksize;
      else
          x=x+blocksize;
      end
  end

message=reshape(message_vector(1:Mo*No),Mo,No);

elapsed_time=cputime-start_time,

subplot(212);imshow(message,[]);title('Recovered Message')
subplot(211);imshow(watermarked_image,[]);title('Watermarked Image')

[Walter Roberson]

No idea. I do not pay attention to how watermarks are calculated or embedded.

[Davinderjeet]

this code resulted in the error written below

??? subplot(212);imshow(message,[]);title('Recovered Message') subplot(211);imshow(watermarked_image,[]);title('Watermarked Image')
                                                               |
Error: Unexpected MATLAB expression.

please help me rectify it

[Walter Roberson]

On the line

elapsed_time=cputime-start_time,

change the comma to semi-colon

elapsed_time=cputime-start_time;

[Davinderjeet]

thank you Walter Roberson for your timely response.

[Davinderjeet]

Walter can you please provide code for DWT watermarking of images.

[Davinderjeet]

and Walter if you could suggest a good topic related to watermarking that can be persued for m.tech?

[Walter Roberson]

As I indicated above, "I do not pay attention to how watermarks are calculated or embedded."

[Davinderjeet]

can you please suggest some websites for getting the code???

[Davinderjeet]

walter roberson please if you could suggest some topic for thesis work or websites which could be of some help. thank you

[Walter Roberson]

http://www.springer.com/computer/security+and+cryptology/book/978-3-642-32008-8

Answer 2

[Lester]

How do you go about embedding the watermark in the color planes? I didn't get you sir

[Walter Roberson]

Currently you have

cover_object=double(rgb2gray(imread(file_name)));

Change that to

cover_image = imread(file_name);
cover_object = double(cover_image(:,:,1));  %red plane

Then after you have created watermarked_image but before you write it out,

watermarked_red = cast(watermarked_image, class(cover_image));
watermarked_image = cat(3, watermarked_red, cover_image(:,:,[2 3]));

[Lester]

Thank you sir. It worked perfectly fine. You solved all my problems.

[Amanurdeep Ka]

hi, m also getting the same error "index exceeds matrix dimensions" in the above code , I have also made the changes told by Walter Roberson i.e.

Currently you have

cover_object=double(rgb2gray(imread(file_name)));

Change that to

cover_image = imread(file_name); cover_object = double(cover_image(:,:,1)); %red plane

Then after you have created watermarked_image but before you write it out,

watermarked_red = cast(watermarked_image, class(cover_image)); watermarked_image = cat(3, watermarked_red, cover_image(:,:,[2 3]));

BUT STILL GETTING THE SAME ERROR. CAN ANYBODY HELP ME.

[Nova Sri Wahyuni]

how to recover watermarking color image?

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/?term=tag%3A%22watermarking%22