ColorConversions

work under construction.

Should cover RGB->YUV conversions and lumarange scaling/preservation and when to use which conversion.

Color conversions

coefficients	Rec.601	Rec.709	FCC
Kr : Red channel coefficient	0.299	0.2125	0.3
Kg : Green channel coefficient	0.587	0.7154	0.59
Kb : Blue channel coefficient	0.114	0.0721	0.11

(0.0 <= [Y,R,G,B] <= 1.0) ; (-1.0 < [U,V] < 1.0)

Kg = 1 - Kr - Kb

Y = Kr*R + Kg*G + Kb*B

V = (R - Y)/(1-Kr) = R - G * Kg/(1-Kr) - B * Kb/(1-Kr)

U = (B - Y)/(1-Kb) = - R * Kr/(1-Kb) - G * Kg/(1-Kb) + B

R = Y + V*(1-Kr)

G = Y - U*(1-Kb)*Kb/Kg - V*(1-Kr)*Kr/Kg

B = Y + U*(1-Kb)

Converting to programming values

YUV [0,255] <-> RGB [0,255] (0 <= [r,g,b] <= 255, 0 <= y <= 255, -127.5 < [u,v] < 127.5)

y = Y * 255

v = V * 255

u = U * 255

r = R * 255

g = G * 255

b = B * 255

Since you can divide the factor 255 out, the equations above remain the same (where Y,V,U,R,G,B are replaced by y,v,u,r,g,b).

YUV [16,235] <-> RGB [0,255] (0 <= [r,g,b] <= 255, 16 <= y <= 235, 16 <= [u,v] <= 240)

y = Y * 219 + 16

u = U * 224 + 128

v = V * 224 + 128

r = R * 255

g = G * 255

b = B * 255

References:

http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html

ITU bt.601 ...

ITU bt.709 ...