There is confusion in the video industry concerning the terms legal, illegal, valid and invalid. In 1990, Tektronix published a white paper Solving the Component Puzzle. Valid signals can be translated, encoded, or input to any part of a video system without causing amplitude-related problems. B. These are gamma-corrected signals, and are properly written with prime symbols, R', G', and B'.
Legality relates to each interconnect standard.
Validity relates solely to R'G'B'. R'G'B' combinations outside the unit cube, but having luma and color differences within limits, are invalid, but legal. R'G'B' cube contains both.