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how to do watermarking using dct.

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yashi gautam
yashi gautam 2016-2-1
评论： Ragini Gaikwad 2021-6-14
Respected sir,
I have made the following code for watermarking in dct domain.
org_img= imread('lena.jpg');
img4x4 = mat2cell( org_img, size(org_img,1)/2 * ones(1,2), size(org_img,2)/2 * ones(1,2), size(org_img,3) );
% upper left
red_1= img4x4{1,1}(:,:,1);
green_1= img4x4{1,1}(:,:,2);
blue_1= img4x4{1,1}(:,:,3);
%dct to upper left
img1_r= dct2(red_1);
img1_g= dct2(green_1);
img1_b= dct2(blue_1);
%watermark one
w1= imread('cousins.jpg');
wtr_img1= imresize(w1, 1/2);
red1= wtr_img1(:,:,1);
green1= wtr_img1(:,:,2);
blue1= wtr_img1(:,:,3);
%dct to w1
wtr1_r= dct2(red1);
wtr1_g= dct2(green1);
wtr1_b= dct2(blue1);
%embedding of watermark
fimgr1= img1_r+ 0.01*wtr1_r;
fimgg1= img1_g+ 0.01*wtr1_g;
fimgb1= img1_b+ 0.01*wtr1_b;
%combining first block
wimg1= cat(3, fimgr1, fimgg1, fimgb1);
%first output block
rgb1= idct2(wimg1);
imwrite(uint8(rgb1),'DCTWatermarked1.jpg');
figure;imshow(uint8(rgb1));title('Watermarked Image 1');
It shows the error:
Error using .*
Matrix dimensions must agree.
Error in idct (line 74)
y = ifft(W.*bb);
Error in idct2 (line 53)
a = idct(idct(arg1).').';
kindly guide me how to correct it.

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采纳的回答

Walter Roberson
Walter Roberson 2016-2-1
dct2() and idct2() apply strictly to 2 dimensional matrices. Your wimg1 is 3 dimensional (RGB) so you cannot apply idct2 to it.
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Ragini Gaikwad
Ragini Gaikwad 2021-6-14
Can you please help on this, how to apply idct and then combine

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