Grafisthy News

Sometimes the stars align and everything just works. For example, you may tune in to an HDTV broadcast of Law and Order: Special Victims Unit (which is broadcast as a 1080i signal) with your Samsung CRT HDTV (which displays HDTV signals in a 1080i mode). Well, lucky you the input resolution (the 1080i TV program) and the display resolution (your 1080i CRT TV) match. All is well in the world, and good TV is watched. But what if you had a Sony Grand Wega LCD rear-projection TV?

Those big-screen beauties display HDTV at 720p, not at 1080i! This TV displays HDTV at 720p because the LCD (like the plasma, the DLP, and the LCoS) is a fixed-pixel display. In the case of the Sony Grand Wega, the LCDs that make the display work (see Article 22 for more info) have a resolution of 1386 x 788 pixels roughly equivalent to the 1080 x 720 of 720p HDTV. Well what happens in this case (1080i signal into a 720p display) is that a brainy bundle of chips and software called a scaler or video processor gets involved. A scaler converts one resolution to another, using various mathematical techniques to interpolate what the video signal would look like at a different resolution. Going up or going down? If a scaler is converting a lower resolution to a higher one, the process is called upconversion. The opposite process is called, unsurprisingly, downconversion. Sometimes downconversion is called down-resing because the resolution is moved downward. This term is usually applied in a negative way for example, when an onerous copy-protection system downconverts an HDTV signal to standard-definition simply because you don’t have the right copy-protection software on all your components. The main job of a video-processing system is to up- or downconvert an incoming signal to a different resolution. There are two main benefits of this process for a scaler working with your HDTV:

- Video signals are matched to the best display resolution for a particular model of HDTV, regardless of the signal’s original resolution.

- Standard-definition video signals are upconverted to a higher resolution to look closer to HDTV than standard-definition. Don’t buy anyone’s marketing spiel or sales pitch telling you that his or her scaler will make any TV source into HDTV. Good scalers can produce something very pleasing to the eye, which is close to HDTV. But you can’t create something from nothing real HDTV Video processors may also perform other tasks such as 3:2 pulldown processing (discussed in Article 21), which lets you watch material based on 24-frame-per-second film properly on a 30- or 60- frame-per-second HDTV display. De-interlacing your video The simplest video processors which actually pre-date HDTV are those devices known as line doublers. Line doublers have been used in high-end home theaters for years, in conjunction with fancy (and expensive) front-projection systems. Line doublers are also sometimes called deinterlacers. The job of a line doubler is pretty simple it scales the video by converting an analog (480i) video signal into a progressive scan (480p). By doing this simple trick (effectively a doubling of the scan lines in a CRT TV hence the name), a line doubler greatly smooths out the picture, and reduces the subtle flicker you normally get from an interlaced picture. A line doubler works by saving up both of the fields in an analog TV signal frame, and displaying them twice in a 1⁄30-second time slice. (In analog TV, half of the picture is transmitted every 1⁄60 of a second, which is a field; the whole image is called a frame. Article 21 covers fields and frames.)

You also hear about devices call line quadruplers, which not only deinterlace video, but also interpolate in between the lines, to create a picture that’s the equivalent of 960p (twice the resolution of 480p). Line quadruplers are really high-end devices for use with the most expensive ($40,000 and up) CRT front-projection HDTVs. Getting fancy with scaling The advent of fixed-pixel HDTV displays plasmas, LCDs, DLPs and LCoS created a need for something beyond just a simple line doubler (not that a line doubler is all that simple!). Many fixedpixel displays actually have rather funky native resolutions that require all incoming video signals to be scaled. doesn’t have a native resolution of exactly 720p (1280 x 720 pixels); it actually has a resolution of 1386 x 788: Every signal, even 720p signals, must be converted to the higher resolution! This demand has led to the development of scalers that convert any incoming video signal (well, any standard incoming video signal) into a specified output resolution. Choosing Scalers We don’t want to make you think about scalers too much. If your HDTV needs a scaler to operate (and most need at least a deinterlacer/ line doubler), then it already has one built in. Let’s repeat that: If your HDTV needs a scaler, that scaler should be in there already. You don’t need to spend even more money! There are, however, some limitations to internal scalers. Sometimes an external scaler offers advantages. Here are three scenarios that may call for an external scaler:

- Some HDTVs have internal scalers that accept signals of only certain resolutions. For example, some HDTVs may accept only 480i, 480p and 1080i inputs. If your external HDTV tuner puts out only a 720p signal (admittedly rare), you’re out of luck.

- Some HDTVs (CRT tube-based TVs, either direct-view or projection systems, usually) contain an internal scanner that deinterlaces analog video sources (that is, converts 480i to 480p) but doesn’t upconvert analog signals to a higher resolution. There’s nothing wrong with this 480p will probably look better than analog’s ever looked! but the picture won’t be using the full capacity of your HDTV.

- You may just be a person who wants the best! The scalers built into most HDTVs are good enough for most owners. But, if you demand those last few percentage points of picture perfection from your system, you may want a fancier external scaler. Just to give you an idea of what an external scaler is all about, we mention a popular (and well-reviewed) model: the DVDO iScan HD. This scaler (which retails for $1,499) can convert any incoming video signal to any resolution between 480p and 1080p (yes, we said, 1080p that is one of the 18 ATSC standards, but it isn’t commonly used because almost no HDTVs can display that high a resolution). And, if your display has a funky native resolution, that’s no problem the iScan HD can be programmed for custom resolutions, too! The iScan HD also does a bunch of other cool stuff, too:

- It acts as a video-switching hub, so you can run all of your source devices through it. (See Article 19 for more on video switching.)

- It switches and routes analog and digital audio signals as well.

- It has a special circuit “Precision AV LipSync” that makes sure your video and audio are perfectly matched up even if the original broadcast isn’t! No more movies that look like poorly dubbed Kung Fu flicks.

- It includes a computer interface, so you can download software upgrades over the Internet to keep your iScan HD up to date. You can find out more about the iScan HD at the following URL: www.dvdo.com/pro/pro- ishd.html

SOURCE : http://www.web-articles.info/e/a/title/Magic-Black-Boxes-What-the-Heck-is-a-Video-Processor/