<A HREF="COL_.htm"><img align=center src="contents.gif" ALT="Contents"></A>   ## American Y'I'Q'

American TV (NTSC coded) uses Y'I'Q' components. Again Y' is similar to perceived luminance, I' and Q' carry colour information and some luminance information and are derived by rotating the U'V' vector formed by colour coding as described in section 3.1 by 33 degrees. The Y' signal usually has 4.2 MHz bandwidth in a 525 line system. Originally the I' and Q' signals were to have different bandwidths (0.5 and 1.5 MHz) but they now commonly have the same bandwidth (1 MHz). The coding is also used in some 625 line countries with NTSC subcarriers, again mostly in the Americas. The CRT gamma law is assumed to 2.2. The system white pointis Illuminant C, the chromaticity coordinates are:-

```    R:      xr=0.67      yr=0.33
G:      xg=0.21      yg=0.71
B:      xb=0.14      yb=0.08
White: xn=0.310063 yn=0.316158 zn=0.373779
```
The conversion equations for linear signals are:-

```    X = 0.607*R + 0.174*G + 0.200*B
Y = 0.299*R + 0.587*G + 0.114*B
Z = 0.000*R + 0.066*G + 1.116*B
```
```
R = 1.910*X - 0.532*Y - 0.288*Z
G =-0.985*X + 1.999*Y - 0.028*Z
B = 0.058*X - 0.118*Y + 0.898*Z
```

The coding equations for non-linear signals are:-

```    Y'= 0.299*R' + 0.587*G' + 0.114*B'
I'=-0.27*(B' - Y') + 0.74*(R' - Y') = 0.596*R' - 0.274*G' + 0.322*B'
Q'= 0.41*(B' - Y') + 0.48*(R' - Y') = 0.212*R' - 0.523*G' - 0.311*B'
```
```
R'= Y' + 0.956*I' + 0.621*Q'
G'= Y' - 0.272*I' - 0.647*Q'
B'= Y' - 1.105*I' + 1.702*Q'
```

It is possible to define a transformation matrix between EBU Y'U'V' and NTSC Y'I'Q'. However, this only makes sense if the primaries are the same for the two systems, and clearly they are defined differently. However, over the years, the American NTSC system has changed its primaries several times until they are now very similar to those of the EBU systems. The non-linear connecting equations are:

```     I'=-0.27/0.493*U' + 0.74/0.877*V' =-0.547667343*U' +  0.843785633*V'
Q'= 0.41/0.493*U' + 0.48/0.877*V' = 0.831643002*U' +  0.547320410*V'
```
and:

```     U'=-0.546512701*I' +  0.842540416*Q'
V'= 0.830415704*I' +  0.546859122*Q'
```
To all intents and purposes these equations are identical and so one practical set of equations can be used in either direction:

```     I'=-0.547*U' + 0.843*V'
Q'= 0.831*U' + 0.547*V'
```
```
U'=-0.547*I' + 0.843*Q'
V'= 0.831*I' + 0.547*Q'
```

The conversion equations relating NTSC RGB signals to EBU and 709 are:

```    Rntsc= 0.6984*Rebu + 0.2388*Gebu + 0.0319*Bebu
Gntsc= 0.0193*Rebu + 1.0727*Gebu - 0.0596*Bebu
Bntsc= 0.0169*Rebu + 0.0525*Gebu + 0.8450*Bebu
```
```
Rebu= 1.4425*Rntsc - 0.3173*Gntsc - 0.0769*Bntsc
Gebu=-0.0275*Rntsc + 0.9350*Gntsc + 0.0670*Bntsc
Bebu=-0.0272*Rntsc - 0.0518*Gntsc + 1.1081*Bntsc
```

and:

```    Rntsc= 0.6698*R709 + 0.2678*G709 + 0.0323*B709
Gntsc= 0.0185*R709 + 1.0742*G709 - 0.0603*B709
Bntsc= 0.0162*R709 + 0.0432*G709 + 0.8551*B709
```
```
R709= 1.5073*Rntsc - 0.3725*Gntsc - 0.0832*Bntsc
G709=-0.0275*Rntsc + 0.9350*Gntsc + 0.0670*Bntsc
B709=-0.0272*Rntsc - 0.0401*Gntsc + 1.1677*Bntsc
```