A video signal has at least a first signal component corresponding to a first color, and a second signal component, associated with the first signal component and corresponding to a second color. Each signal component is divided into blocks, and each block has one or more encodable units. The encoding of at least one encodable unit of the second signal component is switchable between first and second modes. A method of encoding the signal comprises excluding, for at least one encodable unit of the second signal component, use of the second mode for the encoding of the second-signal-component encodable unit concerned when at least one predetermined condition is satisfied relating to an encoded block or encodable unit of the first signal component that corresponds to the second-signal-component encodable unit concerned.