I did PVD modulus steganography in matlab.The Hiding process is correct and it shows the stego image.But the retrieval process is not correct. Can any one please sort out the problem in the retrieval process.

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Anushka
Anushka on 1 Oct 2015
Answered: Walter Roberson on 2 Oct 2015
I did PVD steganography in matlab. The Hiding process is correct and it shows the stego image.But the retrieval process is not correct. Function CreateeStego hides the secret, im1 is the cover image and im2 is the secret image. Function RecovrSecret retrieves the secret form the stego image. The input to the RecoverSecret is the stego image, this function is not working properly it only shows busy, does not obtains the output.
function [ Steg,capacity ] = CreateeStego( im1,im2 )
cCap = 0;
for dim = 1: 3
em = im2(:,:,dim);
em = em(:);
len = length(em);
in = [];
in=[in dec2bin(len,20)];
for i=1:len %character convert to binary
in=[in dec2bin(em(i),8)];
end
a = im1(:,:,dim); %get cover image
[r,c]=size(a);
final=double(a);
next=0;
capacity=0; %bit space that can be embedded
for x=0:1:r-1 %traverse through all the pixel value on
for y=0:2:c-1 %the image by 2 consecutive pair non overlaping pixel
g=a(1+x,1+y:2+y);
g=double(g);
d=g(1,2)-g(1,1); %d=difference between 2 pixel
lb=[0 8 16 32 64 128]; %lowerbound
ub=[7 15 31 63 127 255]; %upperbound
dap=abs(d);
for i=1:1:6 %test the R boundary
if(dap >= lb(i)&& dap <= ub(i))
n=ub(i)-lb(i)+1; %quantization width of range
t=log2(n); %maximum bit can be embedded between 2 pixel
capacity=capacity+t;
nt=2^t;
FREM =mod((g(1,1)+g(1,2)),nt);
if(next>length(in))
m=0;
m1=0;
elseif(next+t>length(in))
if(1+next>=length(in))
k=zeros(1,t);
else
k=in(1+next:length(in));
end
diff =next+t-length(in);
k1=zeros(1,t);
if(diff>0)
for j=1:next+t-length(in)
k1(j)=k(j);
end
end
k=k1;
next=next+t;
%k=int2str(k);
k=bin2dec(char(k));
if(1+next>length(in))
m=0;
m1=0;
else
m=abs(FREM-k);
m1=2^t-abs(FREM-k);
end
else
k=in(1+next:t+next);
next=next+t;
k=bin2dec(char(k));
m=abs(FREM-k);
m1=2^t-abs(FREM-k);
end
end
end
if(FREM>k && m<=((2^t)/2) && g(1,1)>=g(1,2))
P0=[g(1,1)-ceil(m/2) g(1,2)-floor(m/2)];
elseif (FREM>k && m<=((2^t)/2) && g(1,1)<g(1,2))
P0=[g(1,1)-ceil(m/2) g(1,2)-floor(m/2)];
elseif (FREM>k && m>((2^t)/2) && g(1,1)>=g(1,2))
P0=[g(1,1)+ceil(m1/2) g(1,2)+floor(m1/2)];
elseif (FREM>k && m>((2^t)/2) && g(1,1)<g(1,2))
P0=[g(1,1)+ceil(m1/2) g(1,2)+floor(m1/2)];
elseif (FREM<=k && m<=((2^t)/2) && g(1,1)>=g(1,2))
P0=[g(1,1)+ceil(m/2) g(1,2)+floor(m/2)];
elseif (FREM<=k && m<=((2^t)/2) && g(1,1)<g(1,2))
P0=[g(1,1)+ceil(m/2) g(1,2)+floor(m/2)];
elseif (FREM<=k && m>((2^t)/2) && g(1,1)>=g(1,2))
P0=[g(1,1)-ceil(m1/2) g(1,2)-floor(m1/2)];
elseif (FREM<=k && m>((2^t)/2) && g(1,1)<g(1,2))
P0=[g(1,1)-ceil(m1/2) g(1,2)-floor(m1/2)];
end
if((g(1,1)==0 || g(1,2)==0)&&(P0(1)<0 || P0(2)<0))
P1=[P0(1)+((2^t)/2) P0(2)+((2^t)/2)];
final(1+x,1+y)=P1(1,1); %replace new pixel value into final
final(1+x,2+y)=P1(1,2);
elseif((g(1,1)==255 || g(1,2)==255)&&(P0(1)>255 || P0(2)>255))
P1=[P0(1)-((2^t)/2) P0(2)-((2^t)/2)];
final(1+x,1+y)=P1(1,1); %replace new pixel value into final
final(1+x,2+y)=P1(1,2);
elseif(dap>128)
if(P0(1)<0 && P0(2)>=0)
P1=[0 P0(1)+P0(2)];
final(1+x,1+y)=P1(1,1); %replace new pixel value into final
final(1+x,2+y)=P1(1,2);
elseif(P0(1)>=0 && P0(2)<0)
P1=[P0(1)+P0(2) 0];
final(1+x,1+y)=P1(1,1); %replace new pixel value into final
final(1+x,2+y)=P1(1,2);
elseif(P0(1)>255 && P0(2)>=0)
P1=[255 P0(2)+(P0(1)-255)];
final(1+x,1+y)=P1(1,1); %replace new pixel value into final
final(1+x,2+y)=P1(1,2);
elseif(P0(1)>=0 && P0(2)>255)
P1=[P0(1)+(P0(2)-255) 255];
final(1+x,1+y)=P1(1,1); %replace new pixel value into final
final(1+x,2+y)=P1(1,2);
end
else
final(1+x,1+y)=P0(1,1); %replace new pixel value into final
final(1+x,2+y)=P0(1,2);
end
end
end
Steg(:,:,dim) = final;
cCap = cCap + capacity;
end
display('Embedded Successfully');
end
function RecIm = RecovrSecret(Image)
msg = [];
flag = 0;
[row,col,dim]=size(Image);
j=0;
length=0;
for p = 1:dim
layer = Image(:,:,p);
for x=0:1:row-1
for y=0:2:col-1
gp=layer(1+x,1+y:2+y);
gp=double(gp);
nd=abs(gp(1,2)-gp(1,1));
lb=[0 8 16 32 64 128];
ub=[7 15 31 63 127 255];
for i=1:1:6
if(nd>=lb(i)&&nd<=ub(i))
w=ub(i)-lb(i)+1;
t=log2(w);
FREM=mod(gp(1,1)+gp(1,2),2^t);
k=dec2bin(FREM,t);
msg = [msg k];
j=j+t;
if(flag==0 && j>=20)
length=bin2dec(msg(1:20))+3;load tab; %possible 3 char error
length=length*7;
flag=1;
end
if(flag==1 && j>=length)
w=1;
for q=20:7:length-7
finalIm(w)=bin2dec(msg(1+q:7+q));
w=w+1;
end
end
end
end
end
end
RecIm(:,:,p) = reshape(finalIm,[256,256]);
end
end

Answers (1)

Walter Roberson
Walter Roberson on 2 Oct 2015
All of your "for" loops in the image recovery have finite length, and you have no "while" loops. Your image recovery therefore must terminate at some point. It might take a long time, but it will finish.
You should use the debugger to trace the execution of the routine and figure out where it is spending its time. You could pass in small images to verify that it is working.

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