Human Visual System based watermarking scheme

Im working on a medical image watermarking project. The algorithm is something like this:

• Apply DWT on host image to obtain LL,HL,LH and HH.
• Segment LL band into ROI and RONI, and divide RONI into blocks 4x4
• Apply HVS on selected blocks to select most suitable blocks for embedding watermark info
• Apply DCT on each selected block
• Divide C into 2x2 blocks
• Aplly SCD to generate U, S and V for each sub-block
• Insert the watermark bit by altering the elements S1(1,1) and S2(1,1) according to algorithm
• 
• Inverse SVD, inverse DCT for each sub-block and inverse DWT on the end to get watermarked image

I have done all of this, but without the HVS. I know HVS is entropy:

If somebody can help me with this, I would be very grateful.

Code for embedding watermark which i wrote is here:

for i=1:duz1
   for j=1:duz1
       blokic=cell2mat(RONIdiv(i,j));
       DCTblok=dct2(blokic); %dct transformacija bloka
       RONIDCTdiv(i,j)=mat2tiles(DCTblok,[4,4]); 
       uslov1=all(all(DCTblok)); %da su sve vrijednosti bloka != 0
       BinaryBlok=cell2mat(BinaryMaskdiv(i,j));
       uslov2=~any(any(BinaryBlok)); %da su sve = 0 (samo roni)
       if(k<=256 && uslov1 && uslov2)
           pozblok(p,1)=i;
           pozblok(p,2)=j;
           p=p+1;
           blok=mat2tiles(DCTblok,[2,2]); %dijeljenje u blokove 2x2
           b1=cell2mat(blok(1,1));
           b2=cell2mat(blok(1,2));
           b3=cell2mat(blok(2,1));
           b4=cell2mat(blok(2,2));
           [u1,s1,v1]=svd(b1); %svd transformacija svakog bloka
           [u2,s2,v2]=svd(b2);
           [u3,s3,v3]=svd(b3);
           [u4,s4,v4]=svd(b4);
           m1=abs(s1(1,1)+s2(1,1))/2; %algoritam 1
           if(wat1seq(k)==1)
               s1(1,1)=sign(s1(1,1))*m1+T/2;
               s2(1,1)=sign(s2(1,1))*m1-T/2;
           else
               s1(1,1)=sign(s1(1,1))*m1-T/2;
               s2(1,1)=sign(s2(1,1))*m1+T/2;
           end
           m2=abs(s3(1,1)+s4(1,1))/2; %algoritam 2
           if(wat2seq(k)==1)
               s3(1,1)=sign(s3(1,1))*m2+T/2;
               s4(1,1)=sign(s4(1,1))*m2-T/2;
           else
               s3(1,1)=sign(s3(1,1))*m2-T/2;
               s4(1,1)=sign(s4(1,1))*m2+T/2;
           end
           isvd1=u1*s1*v1'; %nakon promjene s1,s2,s3,s4 (1,1) inverzna svd
           isvd2=u2*s2*v2';
           isvd3=u3*s3*v3';
           isvd4=u4*s4*v4';
           abc=[isvd1,isvd2;isvd3, isvd4];
           DCTblok=abc; %ukoliko je ušlo u petlju stavi?e watermarkirani blok
           k=k+1; %slede?i bit watermarkova
       end
       DCTblokinv=idct2(DCTblok); %inverzna dct
       RONInovi(i,j)=mat2tiles(DCTblokinv,[4,4]); 
   end
end