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The Glossary | Back to the Journal |
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A
Active Matrix
Term used to describe LCD Displays which have micro-transistors that "open" and "close" each pixel.
Active Matrix TFT
A common type of LCD used in laptops, cameras, and LCD projection panels that were produced in the late 1980s to early 1990s. A typical active matrix TFT display is a single panel of LCD glass that controls all three primary colors. TFT displays are noted for their quick response time and their ability to display full motion video and animations without image ghosting.
Aliasing
Jagged edges along the outer edge of objects or text. Anti-aliasing refers to software adjustments that correct this effect. This effect is created by inadequate sampling techniques in computer-produced images.
Ambient Light
Any light in the viewing room created by a source other than the projector or screen.
ANSI Contrast
Contrast is the ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for the same projector
ANSI Lumens
ANSI stands for American National Standards Institute. It is a standard for measuring light output. Different lamps play a role on light output. Halogen lamps appear dimmer than another metal-halide, even if the two units have the same ANSI lumen rating. Type of LCD technology (active matrix TFT, Poly-Si, passive), type of overall technology (LCD vs. DLP vs. CRT), contrast ratios, among other factors can also affect the end result.
Aspect Ratio
The ratio of height to width of a frame or screen. In a 4:3 aspect ratio, the width of the image is 4/3 times the height. Most current TV and computer video formats are in a 4:3 aspect ratio. A 15 inch monitor is 12 inches wide by 9 inches high (9*4/3 = 12). A resolution of 640x480 is a 4:3 format (480*4/3 = 640). SXGA is a 5:4 aspect ratio is (1280x1024), HDTV is 16:9 for that movie theater feel, and 35mm slides are 3:2.
Native aspect ratio refers to the aspect ratio of the physical displays built into the projector. For example, a 1280 x 720 pixel display has a 16:9 native aspect ratio. A display that is 640 x 360 pixels is also a 16:9 aspect ratio, but with a fourth of the resolution of the other display.
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B |
Backlit
A remote control, projector control panel, or other object illuminated from behind. This can be helpful when working in darkened rooms.
Bandwidth
The frequency range of a particular transmission method. In video systems, this value is expressed in MHz, and the better the signal, the greater the bandwidth required.
Bit Mapped Graphics
The type of graphic that is defined and addressed on a bit-by-bit basis which makes all points on the screen display directly accessible.
BNC
Used with coaxial cables, this connector receives all R, G, B, H-Sync and V-Sync information, and composite video.
Build Slide
"Build series" slides show audiences where a topic is heading a line at a time. Each new line added appears in a bright color while previous the line drops back to a darker color.
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Color Resolution
The total number of colors available, expressed in bits per pixel.
Color Temperature
A method of measuring the "whiteness" of a light source. Metal halide lamps produce higher temperatures than halogen or incandescent lights.
Contrast Ratio
The ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for the same projector.
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dB
dB or decibel, is a measure of the power ratio of two signals. In system use, a measure of the voltage ratio of two signals, provided they are measured across a common impedance.
Desktop Videoconferencing
Videoconferencing via personal computer.
Diagonal Screen
One corner of a screen to the opposite corner. A 9FT high, 12FT wide, screen has a diagonal of 15FT. If the screen is 12x12, it would still rate 15FT diagonal since that would be the diagonal usable.
Digital Light Processing (DLP)
Developed by Texas Instruments, DLP is a light processing system that utilized hundreds of thousands of tiny spinning mirrors to reflect images. Many feel it is the most accurate reproduction of color and images available today.
Dot Pitch
The distance between the dots on a CRT display. The closer together the dots are create a higher resolution of a displayed image.
DTV
DTV refers to the three types of digital television including Standard Definition Television (SDTV), Enhanced Definition TV (EDTV), Nad High Definition Television (HDTV).
Dual Scan Passive Matrix
Newer version of the original passive matrix technology, where the screen is controlled by two processing systems. A bit faster than "single scan," response is still horrendously slow, they cannot do multimedia or video either. Contrast remains terrible. Dual scan is used in the least expensive LCD panels.
DVI
DVI means Digital Visual Interface. DVI is a standard that defines the digital interface between digital devices such as projectors and personal computers. For devices that support DVI, a digital to digital connection can be made that eliminates the conversion to analog and thereby delivers an unblemished image.
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EDTV
EDTV stands for extended definition television and is a class of digital television (DTV) that refers to the 480p format. 480p is a progressive scan video format that produces a full frame of 480 lines of video.
EGA
AKA Enhanced Graphics Array, EGA is an image which displays 640 pixels by 350 lines with 16 colors from a palette of 64 colors.
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Field
One half of a video frame consisting of either all of the even-numbered scanlines or all of the odd-numbered scanlines in a frame.
Flat Screen
A CRT made more flat than a standard tube by using more than one electron gun. Beneficial to people who require concise reproduction and great detail such as graphic designers.
Focal Length
Focal length is the distance between the lens and its focal point. A smaller focal length indicates a wider-angle lens.
Front Room Projector or Position
A unit that sits close to the screen, its short throw lens projects an image size that is about the same as the distance to the screen. 6FT diag. screen = 6FT distance. Generally the unit might be as close as 3/4 the screen size or as far as 1.2 times image size.
Full On/Off Contrast
Contrast is the ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for the same projector.
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Genlock
Synchronizing signals between two video sources, which is necessary when overlaying computer graphics on an image from VCR, camera, or videodisc player.
Ghosting
A shadow or weak secondary image as seen on a monitor or display which is created by multiple path broadcast transmission errors.
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HDTV
High-Definition Television. A television system that has twice the standard number of scanning lines per frame and therefore produces pictures with greater detail.
H Sync
AKA Horizontal synchronization. A marker, which indicates to a computer or video signal that it, is the beginning of a line.
High Gain Screen
A screen that uses one of more methods to collect light and reflect it back to the viewing audience, which will increase the brightness of the image over a white-wall or semi-matte screen.
Horizontal Frequency
AKA kHz, the total number of horizontal lines scanned per second in a displayed image.
Horizontal Resolution
The total number of vertical lines individually perceived across the horizontal rows of a monitor.
Hz
AKA Hertz. A measure of frequency in cycles per second. Used to express the frequency of an electrical signal or event.
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I |
Invert Image
Many projectors that are ceiling mounted are mounted upside down. Invert image corrects the image digitally so your projected image is not also upside down.
IR Communication Standard
Many new laptops have an Infra-Red transceiver that follow a recent standard for wireless communicating with peripherals (new laser printers complying with the standard) and networks or desktop systems. If you have a laptop like this, you know the pleasure of walking into a room with a configured laser printer, and printing out documents without having to "plug-in." Only a couple of projectors are now shipping that follow this standard. This allows their remote controls to talk directly to your laptop for remote mousing. A tremendous new capability, as you are normally much closer to your computer than the projector in medium or large rooms.
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JPEG
AKA Joint Photographic Experts Group. An international group, which is working, on a proposed universal standard for the digital compression and decompression of still images used in computer systems. The JPEG idea reduces image size as much as 65:1 and still maintains image integrity by getting rid of subtle color differences the human eye can not see.
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Keystone Correction
A projectors ability to correct the effects of "pointing up" or "pointing down" at a screen enabling the projector users audience to view a rectangular image rather than one with a wider top or bottom.
Keystone
The distortion (usually a wide-top narrow-bottom effect) of a projected image caused by a projector "pointing up" or "pointing down" at its screen. Named after its similarity in shape to the keystone used in constructing an arch.
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Laser Pointer
A hand held device that emits a thin laser beam that focuses a bright dot (usually red) on projected images or just about anywhere. Used by presenters to direct the viewer's eye to a particular point of interest.
LCD
AKA liquid crystal display. This technology comes in many forms, sizes, and resolutions. Its primary purpose is to present a digital image for viewing. They are used in many notebook computer displays and also used as technology inside a projector to project high-resolution digital images.
Lens Shift
The Lens Shift feature of a projector allows the optical lens to be physically shifted up and down (Vertical) or left and right (Horizontal). Most all lens shift mechanisms are motorized with vertical lens shift being the most popular. With a projector that has lens shift you can optically correct for keystone distorted images. It is also used to help geometrically align images when stacking projectors.
Long Throw Lens
A lens designed for projection from the back of a room. Long throw lenses would be used a projection booth in the back of a theater, or from the back of a large classroom. A long throw lens would have to be 50 to 100 FT back to project a 10FT diagonal image.
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Metal Halide Lamp
The type of lamp used in many medium and all high end portable projectors. These lamps typically have a "half-life" of 1000-2000 hours. That is they slowly lose intensity (brightness) as they are used, and at the "half-life" point, they are half as bright as when new. These lamps output a very "hot" temperature light, similar to mercury vapor lamps used in street lights. Their whites are "extremely" white (with slight bluish cast.) and make Halogen lamp's whites look very yellowish by comparison.
Multiplexing
The condensing of many signals into a few or one signal that still represents all of them. An LCD panel performs the de-multiplex function. It takes video signals that contain whole frames of video data and displays them as individual signals on each pixel.
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Native Resolution
Native Resolution refers to the number of physical pixels in a display device. For example, an SVGA projector has 800 physical pixels of resolution horizontally and 600 pixels vertically or 480,000 total pixels. This is the native resolution of the projector. Projectors are capable of projecting greater or smaller resolution images into the same physical resolution through scaling. Scaling reduces the resolution of larger images and increases the resolution of smaller images to match the native resolution of the display device. This type of digital scaling always produces some artifacts in the image that are more apparent when viewing text than graphics or video. Maximum Resolution, as mentioned in the projector specs at ProjectorCentral, refers to the largest resolution that the projector can scale to fit the Native Resolution.
NTSC
The USA’s broadcast standard for video and broadcasting. It is actually a lower resolution than systems used in most of the world. However, by the year 2002 stations will be required to broadcast higher resolution video signals.
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Output
Material that a computer generates from its memory for display on a monitor or for transfer to other media, such as paper or magnetic storage such as zip or floppy disks or a CD-ROM.
Overlay
The capability to superimpose computer-generated graphics and/or text on motion or still video.
Overhead Projector (OHP)
An OHP is designed to project images from transparencies onto a screen.
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PAL
AKA Phase Alternation by Line. The standard color system used throughout Western Europe, except in France.
PanelLink
An all digital interface used to transmit computer video from a PC/Notebook to a projector. Supports resolutions from 640x480(VGA) up to 1600x1200(UXGA). This digital interface might someday replace the analog VGA interface typically used to connect projectors to computers.
Passive Matrix LCD
The original LCDs, these are controlled by a single processing system, for the whole screen, unlike active and poly-si, which have descrete circuits for each "pixel." This results in a panel with terrible color dynamics and contrast (typically 15:1). They are also incredibly slow: On passive laptop computers, the cursor (or anything else) moving on the screen, goes invisible until you stop moving it (submarining) Only one or two projectors use any type of passive matrix display.
Poly-Si (silicon) LCD
A popular LCD technology for the top of the line LCD projectors. Monochrome Poly-Si LCDs are typically placed in each of the three color light paths inside a projector, one each for Red, Green, and Blue. This results in increased color saturation, with contrast ratios above 200:1. Poly-Si technology is also a bit faster than the Active Matrix TFT, for smooth video and multimedia.
Projection Axis
Direction of the "imaginary" line that extends from the center of the projection lens through the center of the screen.
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QXGA
QXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A QXGA display has 2048 horizontal pixels and 1536 vertical pixels giving a total display resolution of 3,145,728 individual pixels that are used to compose the image delivered by a projector. A QXGA display has 4 times the resolution of an XGA display.
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RGB
Red, Green, Blue; the type of monitor generally used with computers. RGB input or output often referred to as Computer input or output.
RCA connector
The connector used with VCRs and stereos for composite video signals and audio.
Real Time
The transfer of data that returns results so quickly that the process appears to be instantaneous.
Rear Projection
Projecting an image through a translucent screen material for viewing from the opposite side. This method of projection is also an option for home theater use in large spaces.
Resolution
Number of pixels (or dots) per unit of area, measure in number of pixels wide by the number of pixels high that can be displayed on the screen or monitor. More pixels per unit of area produce a higher resolution.
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SaBRE
AKA Subtractive Bi-Refringent Effect, a technology that allows two panels rather than three to generate the full 16 color VGA palette. The top panel provides white, magenta, blue, and cyan; the second brings colors from white through yellow and to red.
SECAM
The French broadcast standard (used in some other international markets) for video and broadcasting. Like PAL, SECAM is also a higher resolution than that of the US, until 2002.
Short Throw Lens
A lens designed to project the largest possible image from short distance. Most front room projectors use short throw lens. They are often required for rear projection, where the depth behind the screen is limited. A typical short throw lens might produce a diagonal image size of 10 FT, from a distance of 7 to 10 FT.
Simulated color
Also known as "false color," or "colorized." Projected colors that are not the same as the original image. Some products use a single, colorized LCD, often with purple for dark shades and yellow for light shades (purple background/yellow foreground). Therefore, what should appear on a screen as blue may be yellow, green may be purple.
SVGA
AKA Super VGA. Refers to a computer signal that is higher than the standard VGA resolution of 640 pixels by 480 lines with 16 or 256 colors. SVGA graphics cards may output resolutions such as 1024 x 768, 1280 x 1024, 1600 x 1200 pixels or higher, with 16.7 million colors displayed.
SXGA
SXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SXGA display has 1280 horizontal pixels and 1024 vertical pixels giving a total display resolution of 1,310,720 individual pixels that are used to compose the image delivered by a projector.
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TFT
AKA Thin Film Transistor. A technology used to make Active Matrix LCD panels wherein each pixel has its own transistor switch.
Throw Distance
Length of the projection beam required for a projector to produce and image of a desired size.
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UXGA
Resolution of a computer generated image. A UXGA projector will be able to display a 1600x1200 image from a computer running in a UXGA video mode. If the computer is not running in a UXGA video mode, typically the projector will resize the image to 1600 x 1200.
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VGA Resolution
VGA Resolution normally refers to a 640 x 480 pixel display, regardless of the number of colors available. Originally VGA was 640 x 480 16 colors.
V-Sync
AKA Vertical synchronization. A marker in a video signal for the beginning of a frame.
Vertical Resolution
The total number of horizontal lines that can be perceived in the vertical direction of the screen.
VGA
AKA Video Graphics Array. This is the standard interface for the IBM PS/2. It is the only analog graphics card IBM has used (other cards handle digital information) 720 x 400 in the text mode, graphics mode 640 x 480 resolution.
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Wi-Fi
Wi-Fi is Wireless Fidelity and is based on the IEEE 802.11 specifications for wireless local area networks (WLAN) developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). There are four specifications in the family: 802.11, 802.11a, 802.11b, and 802.11g. All four use the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing.
WSXGA
WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WSXGA display has 1920 to 1600 horizontal pixels and 1080 to 900 vertical pixels respectively that are used to compose the image delivered by the projector.
WXGA
WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1366 to 1280 horizontal pixels and 768 to 720 vertical pixels respectively that are used to compose the image delivered by the projector.
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XGA
Acronym for Extended Graphics Adapter. A standard introduced by IBM that includes VGA as well as resolutions up to 1024 pixels by 768 interlaced lines.
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Y/C Connector
A 4-pin DIN connector used for high-end S-video sources.
Y-Cable
A cable that splits the monitor signal so that it will work simultaneously with both a monitor and a LCD panel.
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Zoom Lens Ratio
Is the ratio between the smallest and largest image a lens can projector from a fixed distance. For example, a 1.4:1 zoom lens ratio means that a 10 foot image without zoom would be a 14 foot image with full zoom. Conversely, a 10 foot diagonal image at 15 feet with no zoom would still be a 10 image at 21 feet at maximum zoom (15 x 1.4 = 21 feet). A zoom lens is "not as bright" as a fixed lens, and the higher the ratio, the less light output.
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