PALplus

PALplus is an extension of the PAL analogue broadcasting system for transmitting 16:9 programs without sacrificing vertical resolution. It followed experiences with the HD-MAC and D2-MAC, standards that were incompatible with existing receivers but featured a 16:9 aspect ratio. It was developed in Germany University of Dortmund in cooperation with German terrestrial broadcasters and European and Japanese manufacturers.

A standard PAL receiver will display the 16:9 image in letterbox format with 432 active lines, while a PALplus receiver can use extra information hidden in the black bars above and below the image to recreate 576 lines of vertical resolution.

A special signal tells the receiver when PALplus is in use, and also whether the original content was interlaced ("Camera mode" 576i50) or progressive scanned ("Film mode" 576p25). An additional signal can enable a "Ghost Cancellation" feature.

A separate feature related to PALplus is ColourPlus, which improves colour decoding performance.

Read more about PALplus:  Operation, PAL-plus Compatible Sets, History, Criticism