With the display intensity corresponding to a given color index ci calculated as
(a) Intensity=0.5[max(r, g, b)+ max(r, g, b)]
(b) Intensity=0.5[min(r, g, b)+ min(r, g, b)]
(c) Intensity=0.5[max(r, g, b)- max(r, g, b)]
(d) Intensity=0.5[min(r, g, b)+ max(r, g, b)]
