Convolution and filtering to refine an image to get the horizontal and vertical edges

img = double(lena);

% ---- Filters ---------------------- % filter to detect horizontal edges

gx = [1;0;-1]./sqrt(2);

% filter to detect vertical edges

gy = [1 0 -1]./sqrt(2); % smoothing filter F = [1 4 6 4 1; 4 16 24 16 4; 6 24 36 24 6; 4 16 24 16 4; 1 4 6 4 1];

F = F./norm(F);

final_img = ?

What are the steps to get to final_img?