Anamorphic Widescreen (aka 'Full Height Anamorphic' - FHA)
When dealing with Standard Definition and Hdv, 'widescreen' pictures have an apparent aspect ratio of 16:9. It it important to understand, however, that this is a kind of 'fudge', in that the aspect ratio of these formats can only be 4:3, and have a frame size of 720x576 square pixels. The 'widescreen' effect is produced by stretching the images within this frame by 133%. This is acheived electronically within the camera, although it can also be done with lenses, and this will result in sharper pictures. A circle on the screen would become 'egg-shaped' (too tall and too narrow). In order to present this picture correctly on a screen that is 16:9 aspect ratio (a 'wide screen') the frame and the imagery within are vertically 'squished back down' to 75% of its original height. If this picture is displayed on a 4:3 ratio screen everything will appear vertically 'stretched'. This picture will need to be 'squished' to 75%, and 12.5% of the screen at the top, and 12.5% of the screen at the bottom will have nothing to display and will appear as 'black bars'. This way of presenting 16:9 pictures on a 4:3 display is called 'letterboxed'.