letterbox: Widescreens just shrunk enough to fit into a narrower image format find space, have black bars at the top and bottom during playback. Since this can be compared to looking through a mailbox slot, this format is referred to as "letterbox".
Corresponding adjustments are often made when displaying on the PAL-Standard format 4:3 necessary. In order to avoid distortions and above all the so-called "eggheads", the image height and width are reduced in the same ratio.
This representation gives away part of the available image area and thus also quality. However, due to the uniform reduction and omission of further conversions, it is a largely native reproduction and is also used, for example, with Blu-ray Cinema format discs such as CinemaScope are used.
An extreme form of "letterbox" is sometimes the image display from 4:3 to 16:9. Incorrect settings in the display device often cause very wide black bars to appear on the right and left, which results in an even greater reduction in the size of the image. However, most TVs can be configured to provide a good compromise between picture size and distortion.