[bob1029]

> is a linear transform of the RGB

It is for every implementation I've seen. I have it defined both ways as 4x4 matrices in my code (3x3 is not in System.Numerics).

[planede]

It appears to be a linear transform from "gamma-adjusted" RGB. So probably not straight from sRGB. [1]

The article does not mention it, but I assume it just takes sRGB color components.

[1] https://en.wikipedia.org/wiki/YCbCr#R'G'B'_to_Y'PbPr