Yu'v' colorspace is a Chromaticity space, since its primary
purpose is to provide two coordinates that display the hue and
saturation of a color. The Y value is that of the XYZ, while the u' and v' are
projections of the X and Y values:

Y = Y |

u' = 4 X / (X + 15 Y+ 3 Z) |

v' = 9 Y / (X + 15 Y+ 3 Z) |

One of the properties of u',v' values is that straight lines in XYZ space remain straight lines in x,y space.

The Chromaticity diagram based on u',v' values is has the advantage over the older x,y based diagram in being more perceptually uniform, and therefore is a preferred space.