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Line Doublers, Quadruplers & Interpolators

Line doublers are very high tech, very expensive, and very impressive electronic devices that double the number of scanning lines (principal manufacturer is Faroudja). They work by examining the initial field (lines 1,3,5, etc.), and then generating, by computer technology, lines of information in between, based on what is contained in the lines above and below. In other words, a new line will be generated between lines 1 and 3, based on what is in those lines, a new line between 3 and 5 based on those lines, and so on. Then the field, made up of the original scanning lines and the computer generated lines, is shown for 1/60th of a second. The second field (lines 2,4,6, etc.) is treated the same way and shown in the next 1/60th of a second. Both IDTV and line doubler technology are considered to be non-interlaced. However, while IDTV adds both fields together and shows them at the same time as a single frame, the line doubler shows each field separately, with computer generated lines added to each field.


Line doubling is an estimation technique, but works very well. To incorporate the most sophisticated line doubling technology into your home theater, you will need a front projection TV system, called a "Data Grade Projector", with RGB (Red, Green, Blue) as well as Sync (Synchronization) inputs, and capable of scanning at a frequency of 31.5 kHz. This is double the scanning frequency of standard NTSC TV (15.75 kHz - which is the product of 30 frames per second multiplied by 525 lines per frame). Some of these projectors are adaptable to the future HDTV (see below), which also uses a high scanning frequency - 4 times the basic NTSC frequency (check with your dealer about upgradability to HDTV). A data grade projector will cost about $10,000 by itself, with the line doubler adding thousands more, so ask plenty of questions and plan for nice long demonstrations if you consider purchasing this type of equipment.

Line quadrupling is now available as an accessory for data grade projectors having 63 kHz scanning frequency capability (4 x the NTSC frequency). The image is spectacular with line quadruplers because no scanning lines are visible, even up close. The cost is high at this point (over $20,000), but if the technology is condensed into a few massed produced computer chips, this dazzling image improvement could become available on consumer NTSC TVs. Lastly, "Interpolators" are available, which determine the optimum scanning frequency for a particular TV, and apply that scanning frequency rather than using doubling or quadrupling. In other words, the scanning frequency may be somewhere in between. Snell and Wilcox make superb interpolators, but the cost is very high ($28,000). They produce beautiful video images, especially with top of the line projectors such as those made by Vidikron. HDTVs have line doubling built-in, and they only cost $7,000, which makes them economical compared to some of the stand alone line doublers.