[Visual functions of DVD-Video] ![]()
A single disc is good for both 16:9 wide-aspect TVs and conventional 4:3 aspect-ratio sets. So users do not need to worry about whether they have a wide-aspect version or a trimmed version. For a wide-aspect picture such as that of Vistasize movies, the Squeeze system is adopted which records wide-aspect pictures in 4:3 aspect ratio by reducing the ratio horizontally. But picture quality does not deteriorate when the movie is viewed on a wide-aspect TV, because the aspect ratio is restored to the original. On a 4:3 TV, a movie can viewed in a Letterbox which reduces vertical size or in Pan & Scan which changes some portions to a 4:3 aspect ratio. Generally, to make it possible for wide-aspect broadcasting and movie software to be displayed on a 4:3 screen, the wide-aspect picture has black bands at the top and bottom. To display the wide-aspect picture on a wide-aspect TV, the picture is zoomed so that the black bands at the top and bottom are beyond the screen. When a wide-aspect picture has these black bands, the number of scanning lines in the top and bottom portions beyond the screen margin is subtracted from the picture. The picture displayed has only about 360 vertical scanning lines, whereas a wide-aspect picture without black bands has 525 (in the case of NTSC), and therefore picture quality deteriorates. Thanks to adoption of the Squeeze system, wide-aspect pictures can be viewed with the original number of scanning lines.
|