Help with my code please!

I attached images from one literature i read and what is written there is what i want to do. Can you guys help me correct my code? Because i can't make it work. :(

 gray_no_OD=im2double(ODRemove);
r=gray_no_OD(:,:,1);
g=gray_no_OD(:,:,2);
b=gray_no_OD(:,:,3);
I=(r+g+b)/3;
MaxI = max(I(:));
MinI = min(I(:));
%subplot(1,2,2); imshow(gray_no_OD)

 bs_r=50;                   %Row value for block segmentation
 bs_c=55;                   %colume value for block (84*84)

 [r, c]=size(gray_no_OD)
kk=0;
q=0;
w=0;
store_orig_image = gray_no_OD;
 % Dividing the Cover image into  bs_r x bs_c Blocks
 for i=1:(r/bs_r)
     for j=1:(c/bs_c)

        feature(:,:,kk+j)=(gray_no_OD((bs_r*(i-1)+1:bs_r*(i-1)+bs_r),(bs_c*(j-1)+1:bs_c*(j-1)+bs_c)));
        mean_block = mean2(feature(:,:,kk+j));
        std_block = std2(feature(:,:,kk+j));
        %===============Sigmoid function================
            for m=1:bs_r
                for n=1:bs_c
                    sigm = inv(1+ exp((mean_block-feature(m,n,kk+j))/std_block));
                    gray_no_OD(m+q,n+w) = 255*((sigm-MinI)/(MaxI-MinI));
                end
            end
        %===============================================
        w = w+55;
     end
     m= m+50;

 kk=kk+(r/bs_c);

 end