work under construction.
Should cover RGB->YUV conversions and lumarange scaling/preservation and when to use which conversion.
| 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)
YUV [0,255] <-> RGB [0,255] (0 <= [r,g,b] <= 255, 0 <= y <= 255, 0 < [u,v] < 255)
y = Y * 255
v = V * 127.5 + 128
u = U * 127.5 + 128
r = R * 255
g = G * 255
b = B * 255
Substituting (Y,V,U,R,G,B) in the equations above and multiplying with 127.5 and respectively 255 gives
y = Kr*r + Kg*g + Kb*b
v - 128 = 0.5*(r - y)/(1-Kr) = 0.5 * r - 0.5 * g * Kg/(1-Kr) - 0.5 * b * Kb/(1-Kr)
u - 128 = 0.5*(b - y)/(1-Kb) = - 0.5 * r * Kr/(1-Kb) - 0.5 * g * Kg/(1-Kb) + 0.5 * b
r = y + 2*(v-128)*(1-Kr)
g = y - 2*(u-128)*(1-Kb)*Kb/Kg - 2*(v-128)*(1-Kr)*Kr/Kg
b = y + 2*(u-128)*(1-Kb)
YUV [16,235] <-> RGB [0,255] (0 <= [r,g,b] <= 255, 16 <= y <= 235, 16 <= [u,v] <= 240)
y = Y * 219 + 16
u = U * 112 + 128
v = V * 112 + 128
r = R * 255
g = G * 255
b = B * 255
http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html
ITU BT.601 ...
ITU BT.709 ...
$Date: 2006/03/26 18:06:55 $