watermark Embedding in Blocks

hello everyone i want to embed watermark in image of size 512*512 & watermark size is 64*64. first of all i am converting original image into 8*8 block. then i want to convert watermark also into 8*8 block and embed it into four block only[16*4 = 64(its my watermark size)]. As i am converting original image into total 4096 block.i want to embed watermark into 64 blocks only. can any one elaborate the coding part for it.my part is as follows

%embedding watermark
for R22=1:64
    Block2(:,:,xx:yy)=Block2(:,:,xx:yy)+ aa*Block5(:,:,1:64);
    xx=64*(R22)+1;
    yy=xx+63;
end;

Here consider Block2 as the blocked original image. aa is the embedding constant and Block5 is named to the watermark image. as here clear that its start embedding again after 64 block. but i want it should embed only first 64 block, not in whole image. thanx in advance

Answer 1

[Walter Roberson]

I think that in some places you mean "pixels", but that possibly in other places you do mean "blocks". Could you go back over your wording and check it?

Your current code is equivalent to the loop-less

Block2 = Block2 + aa * repmat(Block5(:,:,1:64),1,1,64))

but I am not clear as to what your target is.

Answer 2

[Saira Khalid]

can you tell what is the initial value of xx and yy? @ amitesh kumar

[Walter Roberson]

xx = 1; yy = 64;

[Saira Khalid]

I have tried. My code is given below. It's giving an error. Index exceeds matrix dimensions.

Error in block_wise_embedd (line 9) Block2(:,:,xx:yy)=Block2(:,:,xx:yy)+ aa*Block5(:,:,1:64);

Block2=imread('lena.jpg');
Block2=im2double(Block2);
Block2=imresize(Block2,[512 512]);
Block5=imread('logo.jpg');
Block5=im2double(Block5);
Block5=imresize(Block5,[64 64]);
xx = 1; yy = 64; aa=1;
for R22=1:64
  Block2(:,:,xx:yy)=Block2(:,:,xx:yy)+ aa*Block5(:,:,1:64);
  xx=64*(R22)+1;
  yy=xx+63;
end

Please check it how to resolve.

[Walter Roberson]

The original poster appears to have converted the image into an 8 x 8 x (blocks) array. Also I am fairly sure the original poster was working with grayscale rather than RGB (you are almost certainly working with RGB, as you are using JPEG and very few JPEG files are really grayscale -- grayscale JPEG image are almost always RGB images that have all three planes the same value.)

[Saira Khalid]

I have also tried with png . "Index exceeds matrix dimensions." Error

   Block2=imread('erd.png');
Block2=im2double(Block2);
Block2=imresize(Block2,[512 512]);
Block2=rgb2gray(Block2);
imshow(Block2);
Block5=imread('logo.png');
Block5=im2double(Block5);
Block5=imresize(Block5,[64 64]);
xx = 1; yy = 64;aa=1;
for R22=1:64
    Block2(:,:,xx:yy)=Block2(:,:,xx:yy)+ aa*Block5(:,:,1:64);
    xx=64*(R22)+1;
    yy=xx+63;
end

[Walter Roberson]

You have not converted your image into an 8 x 8 x (number of blocks) array. For example you could use https://www.mathworks.com/matlabcentral/fileexchange/25763-tile and then

Block2 = cat(3, tiles{:})

Answer 3

[xingxingcui]

see here: add watermark to image

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