What is an LCD projector

Q. What is a CRT?
CRT is an acronym for cathode-ray tube. It is most familiar to us as what we call a picture tube in our television sets. A standard television set uses one CRT with a special mask inside that allows for small dots or lines of the colors red, green and blue to make up a color image. A 3-tube or 3-CRT projector uses 3 separate CRTs, one for each color. A basic CRT is comprised of a cathode-ray in the neck of the tube and a phosphor coated glass at the front of the tube. The cathode-ray shoots a beam of electrons which strikes the phosphors on the front glass causing them to emit visible light.

Q. What is an LCD panel?
LCD is an acronym for Liquid Crystal Display. An LCD panel is a translucent glass panel that shows a computer or video image using a matrix of tiny liquid crystal displays, each creating one pixel ("picture element," or dot) that makes up the image. Used with an overhead projector for a light source, an LCD panel can make an effective computer projection device, however LCD projectors have become a more economical choice. "LCD panel" also refers to the smaller panels used internally in today's LCD video projectors.


Q. What is an LCD projector?

A self-contained unit that combines one to three LCD panels and a light source for a complete computer and/or video projection device. Generally more convenient and efficient than using a separate LCD panel and overhead, LCD projectors come in a wide variety of sizes and specifications.


Q. Which should I buy, a CRT projector or LCD projector?

CRT projectors provide better results if you'll project from computers with more than one resolution. An LCD projector will give its best results only when your computer output exactly matches the stated resolution of the LCD, but that's not a limitiation of CRTs. CRTs provide better video, because they offer better color and grayscale accuracy. Though they are not as bright overall as LCD projectors, if you can light your room properly, CRTs offer a much better range of brightnesses from highlights to shadows. This is the reason they appear to be as bright or brighter than many LCDs, even though the specs suggest otherwise.

Q. What is a Plasma monitor?

Gas plasma technology is a new way to build flat video and computer monitors. Essentially plasma units have the brightness and look of a CRT monitor, but they offer a much larger image and are thin enough and light enough to hang on any wall. This combination makes them ideal where lighting conditions would favor a monitor, but audience size indicates a projector. Like LCD displays, plasma monitors do not exhibit the distortion and loss of clarity in the corners inherent to CRTs.

Q.What are Phosphors?
Phosphors are the material that emit the visible light that makes up the picture we see from a standard CRT based television, projector, computer monitor or the new plasma displays. In a CRT the phosphors are on the inside of the front glass and are excited by a beam of light from the cathode-ray. In a gas plasma flat display, the phosphors are on the inside of the rear glass of the millions of tiny cells or bubbles. The phosphors are excited by UV light produced by electromagnetically charged plasma in the cell.

Q.What is an ANSI lumen?
An ANSI lumen is a measure of brightness put out by a projection device, as standardized by the American National Standards Institute. Note these are not comparable to "lumens" expressed in non-ANSI terms (and used to measure, for example, the output of overhead projectors).

Q. How many ANSI lumens do I need to get a good image?
This depends on your room lighting conditions and screen size. As a rough guide, a rating of 150 to 300 ANSI lumens is adequate with a 60" diagonal screen with room lights off, but you should look for something in the 400 - 500 range for a 100" to 150" screen with lights dimmed, and at least 800 ANSI lumens when you go to a 300" screen or want to project in bright lighting conditions. Your best bet, of course, is to ask your sales rep to demo the projector under conditions typical to what you’ll see.

Q. What is peak lamp life?
Most LCD projectors use a metal halide source, which offers a very white light and a life of 750 - 4,000 hours or more. They typically do not burn out, but gradually grow dimmer, giving you plenty of warning that it’s time for a replacement. With this type of lamp, total lamp life is not a very useful measurement, as the lamp will continue to function long after they're so dim you won't want to use them. So manufacturers' offer a peak rating—and peak lamp life is the time the lamp will last at 80 - 90% of total brightness.

Q. What is resolution?
The resolution of your computer display measures the amount of detail that can be seen in an image, expressed as the number of distinct horizontal and vertical lines visible on a test pattern.

Q.What are VGA , SVGA, XGA and SXGA?
VGA in an acronym for Video Graphics Array. VGA, SVGA and XGA all measure the resolution of the video signal being output by a personal computer. VGA consists of 640 vertical lines x 480 horizontal lines, SVGA 800 lines x 600 lines, and XGA 1024 x 768, and SXGA 1280 x 1024.

Q.What is horizontal and vertical resolution?
A video or computer image is made up of rows of horizontal and vertical pixels. Its resolution is limited by the number of distinguishable rows, or lines, that the monitor or LCD device can form. "Horizontal resolution" or, more properly, "horizontal lines" is the number of distinct lines that you can count going across the image--but if you look at your monitor, these lines would actually go up and down, or vertically. "Vertical resolution" measures the number of distinguishable lines you can count from top to bottom in the image.

In computer projection, the number of lines is only limited by the signal coming out of the computer and the quality of the projection device. In television, the number of vertical lines of resolution is fixed: the American, or NTSC, standard is 525 vertical lines. The number of horizontal lines will vary with the quality of the monitor or projector used, but is still limited to less than 400 by NTSC standards. This limit is one of the barriers that will be broken by the introduction of Digital Television late in 1998.

Q. What's the difference between VHS and S-VHS?

S-VHS was introduced in response to the criticism of the poor video quality of standard VHS recordings. S-VHS is not just a buzzword, but an entirely different system of recording video signals on VHS size tapes. However, it has never become a widely accepted format for consumers so it is a subject of confusion.

S-VHS records luminance and chrominance (b&w picture and color information, also called Y and C) separately, rather than as a composite signal. By doing this, the deck is able to record and playback a wider bandwidth, or a much higher resolution signal than a normal VHS deck. The signal is also output via a special S-Video connector that also keeps the Y and C signals separate. The result is a much clearer, higher definition picture than VHS can produce. The horizontal resolution of S-VHS is around 400 lines, compared to 240 lines of normal VHS in SP mode.

S-VHS is most often used commercially or by educational institutions where they can record video with an S-VHS camcorder at 400 lines and then edit it on S-VHS editing equipment. This allows editing to be done with a very good signal so that even after multiple copies are made during the process, the final result is still higher than the quality of broadcast television. If standard VHS was used, the end result would be noticeably poor, even to an untrained eye.

Unfortunately, S-VHS rarely finds its way into homes because you won't find movies to rent in S-VHS. Also, if you make your own recording on the required special S-VHS tapes, most standard VHS VCRs won't play them.

Q. What is an S-Video connector?

S-Video connectors are used for a variety of high resolution signals. It was originally developed for use with S-VHS recorders, but is now the standard for DVD players and is also used for converting computer signals to video via a scan converter. The connector has four connections (see diagram), compared with two for a standard video connector. This allows the luminance and chrominance (b&w picture and color, also called Y and C) information to be transmitted separately allowing for a much wider bandwidth and less crosstalk. The wider bandwidth translates to a horizontal resolution of about 400 lines compared with the normal 240 to 320 lines with conventional composite video connectors. Less crosstalk means there will be less "snow" or "color noise" in the picture. For reference, the S-Video connector's pin outs are as follows: Pin 1 - Y ground, Pin 2 - C ground, Pin 3 - Y signal in/out, Pin 4 - C signal in/out.

Q. What are DTV and HDTV?
DTV, Digital Television, is a new broadcast standard that will provide vastly improved picture and sound quality when compared to the current NTSC broadcast standard in the United States. With DTV, viewers can see images up to six times the resolution of their current TV’s. HDTV, High Definition Television, is one of the possible formats that will be transmitted when DTV becomes available. HDTV broadcasts are at the top end of the DTV spectrum. These broadcasts will have the best sound quality, the ability to broadcast in a wide screen format using a 16:9 aspect ratio, and the best picture quality.

Q. Should I hold off buying a TV until I can get a new DTV?
No. The FCC will continue to offer analog broadcast space for television programming at least until the year 2006, and broadcasters will simulcast all broadcasts at least that long. Many experts believe that, due to government rules that must be met before discontinuing analog broadcasts, they will continue well beyond the target year of 2006. This means the TV you buy today will probably be receiving broadcasts for the next 10 years or more, and the life expectancy of a television is only around 8 years. Coupled with the fact that the first DTV sets are costing over $2,000, and that you will be able to buy a digital down-converter for any current set, it doesn't make much sense to hold of television purchases just yet.

Q. What is a simulcasting in regards to DTV?
The simultaneous broadcasting of the same program on analog and digital channels. This will enable your analog TVs to continue to receive the same programs as shown on the digital broadcast, without the need for a DTV down converter box.

Q. What is a "component input" on monitors, TVs and projectors?
A component input is likely to be the preferred connector to be used with digital HDTV tuners and digital VCRs. It works by dividing the chrominance signal into red, green and blue components and a separate luminance component similar to S-Video. Though the new digital systems will also have standard composite outputs, connecting with the component input will improve picture quality and reduce noise by minimizing crosstalk within the video signal.

Q. What is an aspect ratio?
An aspect ratio refers to the dimensions of a television screen or other screen. The ratio refers to the width of the screen in relation to the height of the screen. The aspect ratio of today's traditional TV is 4:3. For comparison, the aspect ratio of a square screen would be expressed as 1:1 or 4:4. The aspect ratio of HDTV will be 16:9. This is similar to the aspect ratio that many motion pictures are shot in. The 16 refers to the width of the screen and the 9 refers to the height of the screen.

Q. What is intelligent compression?
Intelligent compression is a pixel mapping technique also known as ," "SizeWise," "Limesco," or a variety of other names, uses a computer algorithm to map high resolution computer images to a lower resolution LCD. Intelligent compression works much better than plain "compression," which most people do not find acceptable. These algorithms work best going only one step down–using an 800 x 600 projector you can get very good pixel-mapped 1024 x 768 images. Going to 1280 x 1024, the image will be complete, but fuzzy.

Q. What is a video line doubler?
A video line doubler (or scan doubler) increases the number of lines of vertical resolution from 525 to 1,050 lines. Though it starts with a fixed, 525-line signal, the device uses a mathematical algorithm to create 525 more lines in between the lines coming from the signal. The result is a much sharper image.

Q. What is a scan converter?
A scan converter is a device that you connect between your computer and a regular television or monitor to allow them to display computer signals. The idea sounds good, but in reality when you convert a computer signal this way it becomes very difficult, or impossible, to read text, although pictures will look satisfactory. The reason for this becomes obvious if you refer to the above articles on VGA and horizontal and vertical resolution. Even the best televisions or non-data monitors are designed to NTSC standards which gives you a maximum resolution of 400 x 525. VGA computer signals are 640 x 480 and the higher resolution SVGA or XGA are fast becoming the standard making the problem even worse. No matter what you do, you can’t clearly display 640, or more, lines of information on a monitor only capable of 400. So, unless you are planning to display nothing but pictures, or very large text, a scan converter probably won’t do what you hope it will.

Q. What is monitor loopthrough?
An output on the projector or large-screen monitor that allows you to connect additional monitors or projectors to display the same image.

A loopthrough output is commonly used to run a desktop computer monitor at the same time the computer image is being projected--thus allowing you to sit or stand at the computer and always face your audience. Another way to accomplish this goal is to supply a Y-cable with the projector, which allows you to split the signal between your monitor and your large-screen device. Note that this type of Y-cable must be designed specifically for your projector by the manufacturer. Use of the wrong Y-cable with computer signals can damage your equipment.

Generally, monitor loopthrough is not helpful if you're using a laptop computer. The laptop's internal circuitry must split the signal between the laptop's monitor and the external device. Most laptops have such circuitry; some do not.

Q. What is a Firewire?
A Firewire is a connection that's been proposed for digital video devices, and which is beginning to show up on digital camcorders. It consists of six wires: two for power, two for data and two for synchronization.

Q. What is keystone correction?
Keystoning is when your image appears wider at the top or bottom due the projector being positioned somewhere other than the center of the screen. Keystone correction, or lens shift, corrects this rectangular distortion. Most LCD projectors today have a fixed keystone factor (allowing the projector to be placed at about an 8-degree angle lower or higher than the center of the screen), but many allow you to adjust keystoning. Thus you can place the projector on your conference table, on carts of various heights, or mount it on a ceiling of various heights without having to worry about ending up with a distorted image.

Q. What is a wireless mouse control on a projector?
A device that simulates the operation of your computer's mouse from a wireless remote control, generally the same control that operates your projector's other functions.

Q. Why would I want a wireless mouse with my projector?

A wireless mouse unchains you from your computer during presentations. Even if you find it difficult to precisely control the mouse pointer, you'll find it invaluable when using presentation software such as PowerPoint® or Astound®. Just having the ability to click the mouse buttons to advance or reverse the slides in a presentation make it a “must have” item for presenters. Note: If you have problems using the mouse to go backward in newer versions of MS PowerPoint®.