procedure RGB_to_HSV (r,g,b: real; var h,s,v:real):
{Given: rgb each in [0,1].
Desired: h in [0,360] and s in [0,1], except if s=0, then h=UNDEFINED.}
begin
max := Maximum (r,g,b);
min := Minimum (r,g,b);
v := max {This is the lightness}
{Next calculate saturation}
if max .notequal. 0 then s := (max-min)/max;
else s = 0;
if s == 0 then h := UNDEFINED;
delta := max-min
if r = max then
h := (g-b)/delta {Resulting color is between yellow and magenta}
else if g = max then
h := 2 + (b-r)/delta {Resulting color is between cyan and yellow}
else if b = max then
h := 4 + (r-g)/delta; {Resulting color is between magenta and cyan{
h := h*60 {Convert to degrees}
if h < 0.0 then
h := h + 360 {Make degrees be nonnegative}
end {Chromatic Case}
end {RGB_to_HLS}