Lines of horizontal resolution

Lines of horizontal resolution are often confused with scan lines. The two are totally different things, be careful when shopping for equipment. Lines of horizontal resolution refers to visually resolvable vertical lines per picture height. In other words, it's measured by counting the number of vertical black and white lines that can be distinguished an area that is as wide as the picture is high. Lines of horizontal resolution applies both to television displays and to signal formats such as that produced by a DVD player. Since DVD has 720 horizontal pixels (on both NTSC and PAL discs), the horizontal resolution can be calculated by dividing 720 by 1.33 (for a 4:3 aspect ratio) to get 540 lines. On a 1.78 (16:9) display, you get 405 lines. In practice, most DVD players provide about 500 lines instead of 540 because of filtering and low-quality digital-to-analog converters. VHS has about 230 (172 widescreen) lines, broadcast TV has about 330 (248 widescreen), and laserdisc has about 425 (318 widescreen). Scan lines, on the other hand, measure resolution along the y axis. DVD produces 480 scan lines of active picture for NTSC and 576 for PAL. The NTSC standard has 525 total scan lines, but only 480 to 483 or so are visible. (The extra lines are black and are encoded with other information). Since all video formats have the same number of scan lines, it's the horizontal resolution that makes the big difference in picture quality.