Glossary of Terms:
Projection Optics

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Active Matrix LCD
A type of liquid crystal display (LCD) technology where each pixel is actively controlled by a diode or a transistor, allowing greater color and contrast quality than passive matrix LCD. The advantage is that each pixel can be independently controlled.

Active Matrix TFT
A common type od 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.

Ambient Light
Any light in the viewing room created by a source other than the projector or screen.

Anamorphic Lens
An anamorphic lens is a lens that has different optical magnification along mutually perpendicular radii. This provides the ability to project a source image of one aspect ratio, such as 4:3, into a different aspect ratio, such as 16:9, by using different magnifications for the horizontal and vertical dimensions of the projected image.

ANSI Lumens
A measurement of the overall projector brightness, representing the average of 9 points on the projected screen image on a scale devised by the American National Standards Institute (ANSI). Depending on the lamp, optics, and projector design, ANSI lumens range from 200 to 10,000 per projector.

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 x 4/3 = 12). A resolution of 640x480 is a 4:3 format (480 x 4/3 = 640). SXGA is a 5:4 aspect ratio (1280x1024), HDTV is 16:9 aspect ratio, and 35mm slides have a 3:2 aspect ratio.

Auto Balance
A system for detecting errors in color balance in black and white areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

B

Back Room Projector
A projector with a "long-throw" lens designed to be used from the far back of the room, often in a projection booth, balcony, or back of an auditorium. Many typical projectors have third party lenses available for long-throw applications.

Backlit
Refers to a remote control, projection control panel, or other object illuminated from behind. This is an asset when using the projector in a darkened or semi-darkened room. Many projectors have backlit remote controls, while the number of projectors with backlit control panels is much smaller. As projectors have gotten brighter, room lights tend to stay on, making the need for backlit controls less important.

Brightness
The attribute of visual perception in accordance with which an area appears to emit more or less light. (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.) Brightness is measured in lumens on a projector.

Bulb
A light source commonly mistaken for the light source within a projector. Bulbs power incandescent room lighting. Lamps power projectors.

C

Coated Optics
A variety of materials are put on to high quality lenses for several reasons. One of the key reasons is to minimize the amount of light reflected back to the lamp, and the amount of ambient light that mingles with the focused light leaving the lens. Generally, good coatings can add 15% or more to the brightness of a lens. Other coatings are used for filtering colors.

Color Dynamics
"The whitest whites, reddest reds, etc." High color dynamics are a result of dynamic range/contrast ratios. When a unit is described as having excellent color dynamics, the practical description might be "rich colors, excellent definition, and high contrast."

Color Temperature
A method of measuring the "whiteness" of a light source. Metal halide lamps have very high color temperatures compared to halogen or incandescent lights.

Compatibility
Relates to the video and computer signal formats the projector is capable of displaying.

Component Video
Component Video is a method of delivering quality vide (RGB) in a format that contains all the components of the original image. These components are referred to as luma and chroma and are defines as Y'Pb'Pr' for analog component and Y'Cb'Cr' for digital component.

Composite Video Signal
The combined picture signal, including vertical and horizontal blanking and synchronizing signals.

Compressed Resolution
Most projectors automatically accept images that are of greater resolution than the native (true) resolution of the projector. The resulting image is scaled to fit the native resolution of the projector using a variety of scaling algorithms. Not all projectors use the same compression algorithms; therefore, the quality of compression can vary. The nature of compression in a digital device means that some image content is lost.

Compressed SVGA
Unlike CRT monitors, LCD and DLP projectors only have one "true" resolution. Most projectors on the market are VGA (640x480) resolution. To project an 800x600 image to a VGA projector, the original 800x600 signal must be compressed down to VGA. This is done by interpolating the data and trying to best display all the information with only two-thirds of the pixels (307,000 vs 480,000). the resulting image gives you SVGA page size, but some sacrifice of image quality.

Compressed SXGA
Found on XGA projectors, compressed SXGA handling allows these projectors to handle up to 1280x1024 SXGA resolution.

Compressed XGA
Found on SVGA projectors, compressed XGA handling allows these projectors to handle 1024x768 XGA resolution.

Compression Mode
A method of displaying images in a reduced size format. A compressed image usually has part of the image information discarded. The result is a projected image that has light and dark lines and text characters with thick and thin line widths.

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.

Convergence
The alignment of the red, green, and blue video image signals on a projected display system.

D

Diagonal Screen
A method of measuring the size of a screen or a projected image. It measures from one corner to the opposite corner. A 9 foot high, 12 foot wide screen has a diagonal of 15 feet (traditional 4:3 ratio). Even if the screen is 12x12 ft., the diagonal is still 15 feet because that would be the diagonal of the usable area.

Display Size
The diagonal length of the LCD plate. Typical sizes are 8.4" to 12.1".

DLP
Acronym for Digital Light Processing, a data projection technology developed by Texas Instruments using a microprocessor to display bright, colorful images in fully lit rooms. Used primarily in portable and ultra-portable projectors, the DLP chip is the size of a postage stamp and contains millions of microscopic mirrors - one for each pixel - that flip on an axis, reflecting light through a color wheel to create an image.

DVI
Acronym for 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.

F

F-number
Refers to the amount of brightness that a lens allows through the screen. Ideally, the f-number should not deviate much from different zoom angles.

Field
One half of a video frame consisting of either all of the even-numbered scan lines or all of the odd-numbered scan lines in a frame.

Focal Length
The distance from the surface of a lens to its focal point. A smaller focal length indicates a wider-angle lens.

Focus
A point at which rays of light converge. It is adjusted to clarify a blurry image.

Front Room Projection or Position
Front projection is when a projection unit sits in front of the screen.

G

Genlock
Synchronizing signals between two video sources, which is necessary when overlaying computer graphics on an image from a 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.

H

Halogen Lamps
Used in most low and medium priced projectors, these lamps last about 40 hours, with consistent output throughout the lamp life. Although halogens look very white compared to a normal incandescent lamp, they are not a s white as metal halide units. Cost of operation is generally under $0.50 per hour. Most projectors using halogen lamps carry a spare lamp inside.

HDTV
AKA High Definition Television. High definition, wide-screen television broadcasting with digital audio.

High Gain Screen
A screen that uses one or 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.

H Sync
AKA Horizontal synchronization. A marker, which indicates to a computer or video signal that it is the beginning of a line.

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.

I

Image Size
The size of a projected image, usually measured diagonally.

Infra-Red (IR) Remote
The traditional remote control, it transmits infra-red, like a television remote control. Typical range is limited to 30 or 35 feet. Infra-red requires line of sight or a bounce off a hard surface. The presenter must pay attention to where the remote is pointed. Some projectors have an IR sensor in both the front and rear of the projector, which can be useful. When working at or near the maximum distance, pointing directly at the receiver is necessary.

Interlaced Video
Video systems in which each frame of video consists of two video fields. The odd-numbered lines are contained in the first field and the even-numbered lines are contained in the second field. When the image is delivered to a video device, such as a television, the odd and even fields are delivered at 50 or 60 fields per second so you see an integrated image.

Interlacing
Technique used to reduce flicker caused when the first created video field fades while the next is being written.

Invert Image
Many projectors that are ceiling-mounted are mounted upside down. Invert image corrects the image digitally so your projected image does not appear upside down. Projectors typically are ceiling-mounted upside down because most have built-in keystone correction to compensate for the distortion created by "pointing up" from the table to the screen. Usual positioning has the projector nearly even with the bottom of the screen in a table top position, or, when ceiling-mounted, even with the top of the screen.

K

Keystone/Keystoning
Keystoning is the distortion that occurs when the projector is not perpendicular to the screen. Instead of a rectangular image, the incorrect image is typically shown to be wider across the top and shorter across the bottom, resembling the keystone of an arch.

Keystone Correction
Keystone correction makes the projected image rectangular. This can be accomplished by positioning the projector to be perpendicular to the screen. Since this is not always possible, most projectors are equipped with keystone correction that allows the image to be keystone corrected by adjusting optics, making mechanical adjustments, or applying digital correction to the image. Keystone correction can be one or two dimensional and manual or automatic depending on the projector and the manufacturer.

L

Lamp
The bright source of a projector partially responsible for the sharpness and clarity of an image.

Lamp Life
Lamps used in projectors tend not to burn out suddenly, but to dim gradually. Lamp life refers to how long the lamp can be on until it starts to become too dim for adequate use. The life expectancy of the lamp in the projector varies from 40-70 hours on the low end (mainly halogen lamps) to as many as 4,000 hrs. Fortunately, most projectors today have lamps that will last at least 1,000 hours. That may be adequate to meet your needs, but keep in mind that most lamp replacements cost anywhere from $200 to $500. Two of the most common lamp types are metal halide and UHP lamps. Both types project very white light and typically last 750 to 2000 hours. In contrast, halogen lamps have shorter lives and tend to project a more yellow image. Xenon lamps are often used in high-end projectors.

LCD
Acronym for Liquid Crystal Display. Liquid crystals exist in an intermediate state between liquid and solid, and realign under electrical stimulation. This technology comes in many forms, sizes and resolutions. Its primary purpose is to present a digital image for viewing. Exceptionally slim and lightweight, LCDs are commonly used in many notebook computer displays, TV displays, and inside projectors 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 lens shift mechanisms are motorized with vertical lens shift being the most popular. Projectors that have lens shift allow users to optically correct for keystone distorted images. The lens shift feature is also used to help geometrically align images when stacking projectors.

Lenticular
A screen surface with an embossed geometric shaped pattern that affects view/angle performance and reflection of ambient light.

Long Throw Lens
A lens designed for projection from the back of a room. Long throw lenses would be used in a projection booth in the back of a theater, or from the back of a large classroom. Long throw lenses enable a projector to decrease its image size over the standard lens at the same throw distance. With a long throw distance the user is able to project a smaller image so it will fit on the screen. A typical long throw lens might have to be used 50 to 100 feet back to project a 10 foot diagonal image.

Lumen
A unit of measurement of the amount of visible light energy coming from a light source and perceived by the eye. One lumen is the light of one candle power on each square foot of a sphere at a radius of one foot from the light source.

Lux
A standard for measuring light. Numbers provided by manufacturers often do not provide the necessary additional information needed to compare one projector to another.

M

Maximum Distance
Sometimes, though rarely, this refers to the distance from the screen that a projector can focus the image. Most of the time, it is the manufacturer's opinion of how far from a screen the projector can be to cast a useable (bright enough) image in a fully darkened room. Generally, this is very subjective. One projector might quote a distance that allows it to produce a 25 foot diagonal image, while another, brighter projector might quote a distance equal to only a 20 foot diagonal image.

Maximum Image Size
The largest image a projector can throw in a darkened room. This is usually limited by the focal range of the projector's optics.

Menu Driven
This refers to the type of controls on a projector. A typical menu driven system will first offer a menu of major categories, such as Computer, Video, Audio, Display, Options, etc. After selecting a choice from the main menu, another menu appears with more specific options related to your original menu choice. Many projectors which are menu driven also offer the most widely used functions in a non-menu fashion as well. For example, there might be separate buttons on the remote for volume, brightness, contrast, etc.

Metal Halide Lamp
This is the type of lamp used in most high-end, portable projectors. They typically have a half-life of 1000-2000 hours. This means that they slowly lose intensity (brightness) as they are used, and that at the "half-life" point, they are half as bright as when new. Metal Halide lamps output a very "hot" temperature light, similar to mercury vapor lamps used in street lights. Metal Halide whites are super white (with a hint of blue) and make the white light of a Halogen lamp appear very yellowish by comparison.

Mid Room Projector
Designed to sit in a position that is not too close or too far from the screen. For a 10 foot screen, typical placement is 12.5 to 25 feet away. Most mid-room projectors have zoom lenses.

Minimum Distance
The closest position that a projector can focus an image onto a screen.

Multimedia Presentations
The integration of text, art, graphics, photography, animation, audio, and video into presentations.

Multiplexing
The condensing of many signals into a few signals or a single signal that still represents all of the original signals. 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.

N

Native Resolution
The computer resolution that optimizes the projector resolution. When buying a projector, you should always match the resolution of your notebook to the native resolution of your projector.

Network
Connecting two or more computers and/or networkable devices for data sharing or remote control of devices.

Non-Interlaced
Each line is scanned during each total vertical (full) screen refresh.

NTSC
Acronym for National Television Systems Committee, the standard for the United States, administered by the Federal Communications Committee (FCC). NTSC is 525 lines of resolution transferred at a rate of 30 frames per second.

O

Output
Material that a computer generates from its memory for display on a monitor or for transfer to other media.

Overlay
The capability to superimpose computer-generated graphics and/or text on motion or still video.

P

PAL
Known as Phase Alternate Line, PAL is the standard color system for video and broadcasting used throughout Western Europe (except France). The phase of the color carrier alternates from line to line. PAL is 625 lines of resolution transferred at 25 frames per second.

Passive Matrix
The use of simple driver electronics in an LCD projector panel where the pixels are turned on and off using a row-and-column format. the amount of control on each pixel is limited, which results in lower contrast ratios and a slower response time than active-matrix LCD projection panels.

Poly-Si (silicon) LCD
A popular LCD technology for 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 of 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.

Pixel
Short for picture element. The smallest graphic unit that can be displayed on the screen, usually a single-colored dot. A color pixel is a combination of red, green and blue subpixels. Total pixels are usually expressed in horizontal x vertical dimensions (e.g. 640 x 480).

Power Down
A modern term for turning something off.

Power Zoom
A zoom lens with the zoom in and out function controlled by a motor, usually adjusted from the control panel or a remote control.

Progressive Scan
A type of display in which all the horizontal lines of an image are displayed at one time in a single frame. Progressive scan is unlike an interlaced scan in which a frame consists of two separate fields with the first field of odd horizontal lines and the second field of even horizontal lines. Progressive scan is used by projectors, computer monitors, some TVs and HDTV systems, and some digital camcorders.

Projection Axis
Direction of the "imaginary" line that extends from the center of the projection lens through the center of the screen.

Projector
A projector is a device that integrates a light source, optics system, electronics, and display(s) for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. There are hundreds of products available in the market and they are differentiated by their resolution, performance and features. These devices attach to a computer or video device the same as you would connect a monitor.

Q

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 four times the resolution of an XGA display.

R

Real Time
The transfer of data that returns results so quickly that the process appears to be instantaneous.

Rear Screen Projection
Projecting an image through a translucent screen material for viewing from the opposite side. With rear projection, the projector is placed behind the screen, invisible to the audience. It projects onto the screen and the audience sees the image on the other side. Since the image is projected through the screen, the image must be reversed. Good rear projection screens actually produce brighter images than some standard screens. Ideally a projector with a short throw lens is used to avoid wasting space behind the screen. The projector can be placed even with the middle of the screen, without blocking anyone's view, so keystoning is not a problem.

Refresh Rate
The number of times the screen image is "painted" or refreshed per second, expressed in Hz.

Remote
A small handheld device separate from the projector, which contains projector controls, such as volume, brightness, etc. The remote control allows the presenter freedom of movement.

Resolution
The number of screen pixels that can be displayed by a projector. Most units have a standard of 640x480 pixels or 800x600 pixels (VGA and SVGA, respectively). More pixels per unit of area produce a higher resolution, giving more detail in the display of an image. Some higher resolutions include, XGA (1024x768 pixels) and SXGA (1280x1024 pixels).

Response Time
The time it takes for a pixel to turn on and off. Typically measured in milliseconds, an active matrix LCD projection panel's response time is fast enough to display full-motion video and rapid mouse cursor movement.

Reverse Image
Reverse image is a feature found on most projectors that flips the image horizontally. When used in a normal forward projection environment, text graphics, etc. are backwards. Reverse image is used for rear projection.

RGB
Red, Green, Blue. The basic signal components of the color video signal.

RS-232C
A cable that connects a computer and its peripherals.

S

Scaler
A scaler, also know as 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. Nearly all LCD projectors today include some type of video scaler, since they must scale the 525-line image to the native resolution of the projector.

S-Video
A video transmission standard that uses a 4-pin mini-DIN connector to send video information on two signal wires called luminance (brightness, Y) and chrominance (color, C). S-Video is also referred to as Y/C. This format offers a higher quality than composite video, but a lower quality than component video.

SECAM
Sequential Couleur Avec Memorie. The color television standard developed in France. SECAM is mostly used in France and Eastern European countries. 625 lines/50Hz.

Serial Port
A data I/O port on the computer enabling other devices or computers to link with the computer. Also referred to as RS-232C or COM port.

Short Throw Lens
A lens designed to project the largest possible image from a short distance. Most front room projectors use short throw lenses. 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 feet from a distance of 7 to 10 feet. A short throw lens enables the projector to increase its image size over the standard lens at the same throw distance. The user can create larger images at closer distances.

SVGA
Acronym for Super Video Graphics Display. SVGA is used to define a specific display resolution equating to 800x600 pixels.

SXGA
Acronym for Super Extended Graphics Adapter. SXGA is used to define a specific display resolution equating to 1280x1024 pixels.

T

TFT
Acronym for Thin Film Transistor. Projection technology which uses only one transparent panel of LCD cells.

Throw Distance
Also known as projection distance. Throw distance is the distance from the projector to the screen.

U

UHP
Acronym for Ultra High Performance and/or Ultra High Efficiency, a term typically used with metal halide lamps that power ultra-bright projectors.

Uniform Brightness
The lack of brighter or dimmer areas of a projected image across a lighted surface.

USB
Acronym for Universal Serial Bus, a peripheral connection interface for low-speed devices. Notable for its easy swapability.

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 mode, typically the projector will resize the image to 1600x1200.

V

Varifocal Lens
A projector lens that has three focal elements contained in a single assembly.

Vertical Resolution
The total number of horizontal lines that can be perceived in the vertical direction of the screen.

Video Compatibility
Ability of computers and projection units to transmit and receive data to read and/or project various video tape standards, such as NTSC, PAL, SECAM and S-VHS.

Video Standards
The type of video inputs an LCD projector can accept. Leading standards include NTSC, SECAM, and PAL.

VGA
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). 720x400 resolution in text mode, 640x480 resolution in graphics mode.

W

WSXGA
WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defines by the number of individual dots (pixels) that a display uses to create an image. 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 defines by the number of individual dots (pixels) that a display uses to create an image. 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.

X

Xenon Arc Lamp
The same light source used in motion picture projectors, produces pure, white illumination to ensure color accuracy and saturation. Lamps have a stable color over their 1000 hour life.

XGA
Acronym for Extended Graphics Adapter. A graphics standard introduced by IBM that includes VGA and extended resolution up to 1024x768 pixels.

Y

Y-Cable
A cable that splits the monitor signal so that it will work simultaneously with both a monitor and an LCD panel.

Y/C Connector
A 4-pin DIN connector used for high-end and S-Video sources.

Z

Zoom Lens
A lens with a variable focal length providing the ability to adjust the size of the image on a screen by adjusting the zoom lens, instead of having to move the projector closer or further away from the screen.

Zoom Lens Ratio
This is the ratio between the smallest and largest image a lens can project 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 10 foot image at 21 feet at maximum zoom (15 x 1.4 = 21 feet).