image and text steganography

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eng 2014-10-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/160165-image-and-text-steganography

编辑： Walter Roberson 2016-1-11

在 MATLAB Online 中打开

can any one correct this code please ?

this code hide the input message text in the cover image but the encoded message is not the input text (embedded text)

Simple Wavelet Steganography: Hide Message in Image using wavelet Transform Code MATLAB :

%%%%%%%%%%%%%%Encoding.m
clear 
close all
clc
im=imread('cameraman.tif');
wname='haar';
msg='Grasshopper Network';
data=[];
for(i=1:length(msg))
d=msg(i)+0;
data=[data d];
end
imshow(im);
[cA1,cH1,cV1,cD1] = dwt2(im,wname);
dec1 = [cA1 cH1; cV1 cD1 ];
figure;imshow(uint8(dec1));
M=max(data);
data_norm=data/M;
n=length(data);
[x y]=size(cH1);
cH1(1,1)=-1*n/10;
cH1(1,2)=-1*M/10;
for(i=1:1:ceil(n/2))
cV1(i,y)=data_norm(i);
end
for(i=ceil(n/2)+1:1:n)
cD1(i,y)=data_norm(i);
end
CODED1=idwt2(cA1,cH1,cV1,cD1,wname);
figure;imshow(uint8(CODED1))
[x y]=size(cA1);
imshow(uint8(CODED1))
ms=abs(CODED1-double(im));
ms=ms.*ms;
ms=mean(mean(ms))
ps= (255*255)/ms;
ps=10*log10(ps)
imwrite(uint8(CODED1),'Stego.bmp','bmp'); 
return
%%%END of encoding.m%%%%%%%%%%%%%%%%
%%%%%Decoding.m%%%%%%%%%%%%%%%%%
im=imread('Stego.bmp');
[cA11,cH11,cV11,cD11] = dwt2(CODED1,wname);
data=[]
data_norm=[];
n=ceil(abs(cH11(1,1)*10));
M=ceil(abs(cH11(1,2)*10));
for(i=1:1:ceil(n/2))
data_norm(i)=cV11(i,y);
end
for(i=ceil(n/2)+1:1:n)
data_norm(i)=cD11(i,y);
end
data=ceil(data_norm*M)-1;
msg='';
for(i=1:length(data))
msg=strcat(msg,data(i));
end
msg

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Image Analyst 2014-10-28

Attach your m-file with the paperclip icon, or read this.

Geoff Hayes 2014-10-28

在 MATLAB Online 中打开

So some of the characters in the decoded message are off by one. This could be due to the fact that the encoded image, CODED1, is cast as uint8 before being written to file, and then the decoded message is obtained as

data=ceil(data_norm*M)-1;

The subtraction of one works for some of the characters in the message (mapping them back to their original value) while it fails for others. You could contact the author of the code (copied from here), as there seems to be some known problems with the decoding.

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