Thursday, July 27, 2006
On the most elementary level, a video image is comprised of what‚Äôs known as scan lines. These lines are quickly scanned on a video screen, beginning at the top and moving down to the bottom. They can be scanned in an interlaced fashion, in which the lines are divided into a pair of fields. In the first field, odd numbered lines are displayed, then even numbered lines are displayed, resulting in an image frame. Lines can also be scanned in a progressive fashion. This type of scanning is used in digital video and computer monitors. Rather than displaying lines in alternating fields, the lines ‚Äì both odd and even ‚Äì are shown in sequential order.
A video component‚Äôs ability to create an image depends on the amount of vertical lines that are scanned. The more vertical lines, the better the image. In many analog video components, the number of vertical scan lines is designated in a certain type of system. There are three kinds of systems: NTSC, PAL, and SECAM. The standard in the United States, Canada and Mexico, the NTSC system produces 30 frames per second, with a 60 HZ system for picture display. NTSC is an interlaced system. Each field has 262 lines.
PAL is used in Europe a.nd the Middle East, as well as parts of Asia and Africa. It works on a 625 line system, producing 25 frames per second. Its signal is interlaced, and the fields are made up of 312 lines. PAL offers a better picture than NTSC, because it has more scan lines.
SECAM is used in France and Eastern Europe, and it, too, features a 625 line system with 25 frames.
These three systems are the standard in analog components in terms of vertical resolution. As far as horizontal resolution goes, things vary according to the type of component being used.
Progressive scanning represents a significant improvement over the above types of interlaced scanning. This type of scanning was initially created to improve monitor displays with computers. When an image is progressively scanned, the results are clearer, more vivid, and more finely detailed. This type of scanning is now standard with DVDs and components that feature high definition capabilities. Viewers must have a DVD player, a set-top satellite box or a high definition cable connection to take advantage of progressive scan. They also need a TV that has the ability to display progressively scanned video images.