RGB to HSI (Gonzalez and Woods)

I = 1/3(R+G+B) S = 1 - ( 3/(R+G+B))*a where a is the minimum of R, G and B H = cos^(-1) ( (0.5*((R-G)+(R-B))) / ((R-G)^2 + (R-B)*(G-B))^(0.5) ) If S = 0, H is meaningless. If (B/I) > (G/I) then H = 360 - H since H is an angle in degrees we then normalise to 0,1 with H=H/360HSI to RGB (Gonzalez and Woods)

First we restore H to degrees with H = 360*H If 0 < H <= 120 then B = 1/3(1-S) R = 1/3(1+ [(S cos H) / (cos(60 - H))] ) G = 1 - (B+R) If 120 < H <= 240 then H = H - 120 R = 1/3(1-S) G = 1/3(1+ [(S cos H) / (cos(60 - H))] ) B = 1 - (R+G) If 240 < H <= 360 then H = H - 240 G = 1/3(1-S) B = 1/3(1+ [(S cos H) / (cos(60 - H))] ) R = 1 - (G+B)

RGB to HSV (Travis) Given RGB values, find the max and min. V = max S = (max-min) / max If S = 0, H is undefined else R1 = (max-R) / (max-min) G1 = (max-G) / (max-min) G2 = (max-B) / (max-min) if R = max and G = min, H = 5 + B1 else if R = max and G not= min, H = 1 - G1 else if G = max and B = min, H = R1 + 1 else if G = max and B not=main, H = 3 - B1 else if R = max, H = 3 + G1 else H = 5 - R1 H = H*60 (converts to degrees so S and V lie between 0 and 1, H between 0 and 360) HSV to RGB (Travis) Convert H degrees to a hexagon section hex = H / 360 main_colour = int(hex) sub_colour = hex - main_colour var1 = (1-S)*V var2 = (1 -(S * sub_colour)) * V var3 = (1 -(S * (1 - sub_colour))) * V then if main_colour = 0, R = V, G = var3, B = var1 main_colour = 1, R = var2, G = V, B = var1 main_colour = 2, R = var1, G = V, B = var3 main_colour = 3, R = var1, G = var2, B = V main_colour = 4, R = var3, G = var1, B = V main_colour = 5, R = V, G = var1, B = var2 where int(x) converts x to an integer value. (N.B. I haven't implemented this transform.) RGB to HSV (Foley and VanDam) max = maximum of RGB min = minimum of RGB V = max S = (max - min) / max if S = 0, H is undefined, else delta = max-min if R = max, H = (G-b)/delta if G = max, H = 2 + (B-R)/delta if B = max, H = 4 + (R-G)/delta H = H*60 if H < 0, H = H + 360 HSV to RGB (Foley and VanDam) if S = 0 and H = undefined, R = G = B = V if H = 360, H = 0 H = H / 60 i = floor(H) f = H - i p = V*(1-S) q = V*(1-(S*f)) t = V*(1 - (S * (1-f))) if i = 0, R = v, G = t, B = p if i = 1, R = q, G = v, B = p if i = 2, R = p, G = v, B = t if i = 3, R = p, G = q, B = v if i = 4, R = t, G = p, B = v if i = 5, R = v, G = p, B = q where floor is the C floor function.