A=imread('electric.jpg');
figure,imshow(A);
%wypełnienie tablic zerami
I1=A;
I=zeros(size(A));
I2=zeros(size(A));

%maska filtrujaca
F1=[0 1 0;
   1 -4 1;
   0 1 0];
F2=[1 1 1;
    1 -8 1;
    1 1 1];

%Padarray z zerami (obcinanie tablicy)
A=padarray(A,[1,1]);
A=double(A);

for i=1:size(A,1)-2
    for j=1:size(A,2)-2

        I(i,j)=sum(sum(F2.*A(i:i+2,j:j+2)));

    end
end
%I=uint8(I);
I = rgb2gray(I);
figure,imshow(I);title('krawędzie');