Aspect Ratio Converters change picture aspect ratio, usually between 16:9 and 4:3. Other aspect ratios may be also allowed for, such as 14:9, and custom values are often available. Technically, the operation involves independent horizontal and vertical resizing and there are a number of choices for the display of 4:3 originals on 16:9 screens and vice versa (e.g. letterbox, pillar box, full height and full width). Whilst changing the aspect ratio of pictures, the objects within should retain their original shape with the horizontal and vertical axes expanded or contracted equally.
See also: Aspect ratio