BBC Four: 2005-present

BBC Four is a BBC television channel available to digital television viewers in the UK. The part successor (with CBeebies) to BBC Knowledge, the station launched on 2 March 2002.

On 10 September 2005, the channel’s new idents were introduced, based on the theme of “four” and optical illusions, for example a swimming pool where a person on an inflatable ring appears in the bottom left corner, though ripples don’t enter the remaining quarters. Although the image appears as one at the start of the ident by the end it is clearly four separate pics.