B = - ((B' - 0.099) / - 1.099) 1/0.45 to have a range of 0 tol: if -0.081 < (R', G', B') < 0.081 R = R'2.2 R = R' / 4.5 G = G' 2.2 G = G' / 4.5 = B'2.2 B = B' / 4.5 CHAPTER 7.2 Colour spaces To compensate for the nonlinear display, linear RGB used. Thus, these equations are also now used for PAL, data is "gamma-corrected" prior to transmission by the SECAM, 576i, and 576p video systems. inverse transform. RGB values are normalized to have a range of 0 to 1: if (R, G, B) < 0.018 Non-CRT displays R' = 4.5R G' = 4.5G Since they are not based on CRTs, the LCD, LCOS, DLP, and plasma displays have different display transforms. To B' = 4.5B simplify interfacing to these displays, their electronics for (R, G, B) > 0.018 are designed to accept standard gamma-corrected video R' = 1.099R 0.45 - 0.099 and then compensate for the actual transform of the G' = 1.099G0.45 - 0.099 display panel. B' = 1.099B0.45 0.45 -0.099 Extended gamut color spaces, such as scRGB, do ad- ditional processing for below-zero values: Constant luminance problem if (R, G, B) < -0.018 R' = - 1.099 (-R0.45) + 0.099 Due to the wrong order of the gamma and matrix oper- G' = - 1.099 (-G0.45) + 0.099 ations, the U and V (or Cb and Cr) signals also contribute B' = -1.099 (-B0.45) + 0.099 to the luminance (Y) signal. This causes an error in the perceived luminance when the amplitude of U and V is if -0.018 < (R, G, B) < 0.018 not correct. This may be due to bandwidth-limiting U R' = 4.5R and Vor a non-nominal setting of the U and V gain (color G' = 4.5G saturation). B' = 4.5B For low color frequencies, there is no problem. For high Although most PAL and SECAM standards specify color frequencies, U and V disappear and consequently a gamma of 2.8, a value of [1/0.45] is now commonly R', G', and B' degrade to be equal to (only) Y. References 1. Benson, K. Blair, Television Engineering 5. IEC 61966-2-1, 1999, Colour 9. ITU-R BT.601-5, 1995, Studio Handbook. McGraw-Hill, Inc., 1986. Management-Default RGB Colour Encoding Parameters of Digital 2. Devereux, V.G., 1