The results (R,G,B) that you calculate are physical quantities (amount of photons, or Watts). But when you double the amount of photons, the human eye sees it l

The results (R,G,B) that you calculate are physical quantities (amount of photons, or Watts). But when you double the amount of photons, the human eye sees it like 40% brighter, not 2x brighter. RGB values, that you give to the monitor (through the canvas), were constructed according to the human eye, so rgb(40,40,40) looks 2x brighter than rgb(20,20,20). Long story short, when you have your physical Red value between 0 and 1, do Red = Math.pow(Red,1/2.2);