imgorig = imread("image.png");
img = rgb2gray(imgorig);
x = length(img(:,1));
y = length(img(1,:));
for i=1:x
  for j=1:y
    zerone(i, j) = double(img(i, j))/25.5-5;
    imgf(i, j) = uint8(1/(1+exp(-zerone(i, j)))*255);
  endfor
endfor
subplot(1, 2, 1), imshow(img)
subplot(1, 2, 2), imshow(imgf)