1. A method comprising, at one of a video source device and a video sink device: (a) deactivating a video processing function at the one device and sending a command for causing the other of said video source device and said video sink device to activate the video processing function; (b) activating the video processing function at the one device and sending a command for causing the other device to deactivate the video processing function; and (c) based on user input indicating whether (a) or (b) resulted in a preferred video image, effecting (a) or (b).