Help me about my error on index in position 2 exceeds array bounds (must not exceed 800).

after=before;   %Inisialisasi matriks hasil untuk memuat tanda air
for i=1:rm          %Sematkan watermark di mid-band
    for j=1:cm
        x=(i-1)*8;
        y=(j-1)*8;
        if mark(i,j)==1
            k=k1;
        else
            k=k2;
        end;
        after(x+1,y+8)=before(x+1,y+8)+alpha*k(1);
        after(x+2,y+7)=before(x+2,y+7)+alpha*k(2);
        after(x+3,y+6)=before(x+3,y+6)+alpha*k(3);
        after(x+4,y+5)=before(x+4,y+5)+alpha*k(4);
        after(x+5,y+4)=before(x+5,y+4)+alpha*k(5);
        after(x+6,y+3)=before(x+6,y+3)+alpha*k(6);
        after(x+7,y+2)=before(x+7,y+2)+alpha*k(7);
        after(x+8,y+1)=before(x+8,y+1)+alpha*k(8);
    end;
end;

[Walter Roberson]

My guess is that (cm-1)*8+8 == 8*cm exceeds the number of columns in before .

But that is only a guess, as we do not know the size(before) or what the values of rm or cm are.

[TADA]

look here

https://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

always copy the entire error message, and tell us from which line of code it originated

moreover, in general, sample data would go a long way

Answer 1

[TADA]

I have no idea what rm and cm are, but at some iteration

y=(j-1)*8 + 8

is greater than the number of columns in your matrix

under the editor menu, you have the run button, if you expand the run menu you can check the "pause on errors"

to easily debug this error