how can i make the result number from convolution become positive?

this is the result

and this the script;

img=imread('albert.jpg');
F=size(img);
G = [0 -1 0;-1 4 -1;0 -1 0];
FxG = F;

% Konvolusi
[bf, kf] = size(F);
[bg, kg] = size(G);

m2 = floor(bg/2);
n2 = floor(kg/2);

% Penambahan elemen nol
pad = zeros(bf+4,kf+4);
pad(3:bf+2,3:kf+2) = F;
[b_pad,k_pad] = size(pad);

for i = m2+1 : b_pad-m2;
    for j = n2+1 : k_pad-n2;
        temp = 0;
        for k = -m2: m2;
            for l = -n2: n2;
                temp = temp + G(k + m2+1,l+n2+1) * pad(i-k,j-l);
            end
        end
        FxG(i,j) = temp;
        
    end
end
FxG = FxG(2:bf+3,2:kf+3);

Answer 1

[Brian Hart]

Convolution results can be negative.

If you want only positive results, two options are to either take the absolute value of the result, or find the minimum (negative) value in the result, then add its absolute value to the result (shifting all the values positive).