I just have to have a say 
Your method is still the same as the one using tresholding :p
Because adding source with itself leads to double intensities, right? Now if you take whatever goes over 255 to your overflow buffer you get the same values as you would get when tresholding away everything that is below 255/2.
Your method is still the same as the one using tresholding :p
Because adding source with itself leads to double intensities, right? Now if you take whatever goes over 255 to your overflow buffer you get the same values as you would get when tresholding away everything that is below 255/2.