LSB steganography : i can't extract the original messages
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the code is:
embedding code:
c = imread('lena.jpg');
message = 'hellokarthick';
message = strtrim(message);
m = length(message) * 8;
AsciiCode = uint8(message);
binaryString = transpose(dec2bin(AsciiCode,8));
binaryString = binaryString(:);
N = length(binaryString);
b = zeros(N,1); %b is a vector of bits
for k = 1:N
if(binaryString(k) == '1')
b(k) = 1;
else
b(k) = 0;
end
end
s = c;
height = size(c,1);
width = size(c,2);
k = 1;
for i = 1 : height
for j = 1 : width
LSB = mod(double(c(i,j)), 2);
if (k>m || LSB == b(k))
s(i,j) = c(i,j);
else
s(i,j) = c(i,j) + b(k);
k = k + 1;
end
end
end
imwrite(s, '111.jpg');
Extraction:
for i = 1 : height
for j = 1 : width
if (k <= m)
b(k) = mod(double(s(i,j)),2);
k = k + 1;
end
end
end
binaryVector = b;
binValues = [ 128 64 32 16 8 4 2 1 ];
binaryVector = binaryVector(:);
if mod(length(binaryVector),8) ~= 0
error('Length of binary vector must be a multiple of 8.');
end
binMatrix = reshape(binaryVector,8,100);
display(binMatrix);
textString = char(binValues*binMatrix);
disp(textString);
The output is:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/150186/image.png)
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回答(1 个)
Geoff Hayes
2015-5-16
Arjun - I suspect the problem is with the line
imwrite(s, '111.jpg');
You are saving s, the image with the secret message, as a jpeg which is a lossy compression method. This means that you are most likely losing information when you save s in this manner. You can prove this by comparing s with that data which is returned by
sp = imread('111.jpg');
s and sp are most likely not identical and so the LSB extraction method (from above) will fail.
I think that you can do one of two things - save the image as bitmap or set the compression to none as
imwrite(s,'111.jpg','Compression','none');
Try the above and see what happens!
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