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3:2 Pulldown |
The process of matching the frame rate of film (24 frames per second) to the frame rate of video (30 frames per second). In 3:2 pulldown, one frame of film is converted to three fields (1-1/2 frames) of video, and the next frame of film is converted to two fields (1 frame) of video. THis process is repeated (yielding 3 fields of video, 2 fields, 3 fields, 2 fields...) until the film is fully converted to a video of approximately the same length (duration). Most scan doublers, quadruplers, and scalers use the premise that two fields of video equal one frame, but video created via 3:2 pulldown does not follow that pattern.
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Amplifier |
A device used to increase the strength of a signal. An electronic device that takes in an original signal and gives it more power and provides it as an output.
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ANSI |
American National Standards Institute. An ourganization that sets standards for US A/V equipment.
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ANSI Lumens |
A standard for measuring light output, used for comparing projectors. Unfortunately, there are enough variables, that the eye will often disagree radically with the ANSI rating. At best, ANSI lumens do fairly well comparing "apples" to "apples". If however one projector uses Halogen lamps and another metal-halide, the halogen projector will seem noticeably dimmer even if the two units rate the same. Other variables, including type of LCD technology (active matrix TFT, Poly-Si, passive), type of overall technology (LCD vs.DLP vs. CRT), contrast ratios, etc. all effect the end result.
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Aspect Ratio |
The relationship of the horizontal dimension to the vertical dimension. In viewing screens, standard TV is 4:3, or 1.33:1; HDTV is 16:9 or 1.78:1. Sometimes the ":1" is implicit, making TV=1.33 and HDTV=1.78.
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Black Level |
More commonly referred to as "brightness," the black level is the level of light produced on a video screen. The level of a picture signal corresponding to the maximum limit of black peaks. The bottom portion of the video wave form, which contains the sync, blanking, and control signals. THe black level is set by the brightness control.
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Brightness |
The attribute of visual perception in accordance with which an area appears to emit more of less light. (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.) - see ANSI Lumen.
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Burn-in |
In a video display, this term describes what happens when an image has been displaying too long, resulting in a permanent image being burned into the screen phosphor.
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Component Video |
Color television systems start with three channels of information: red, green, and blue (RGB). In the process of translating these channels to a single composite video signal, they are often first converted to Y, R-Y, and B-Y. Both 3-channel systems, RGB and Y, R-Y, B-Y, are component video signals. They are the components that eventually make up the composite video signal. Higher quality program production is possible if the elements are assembled in the component domain.
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Composite Video |
An all-in-one video signal comprised of the luma (black and white), chroma (color), blanking pulses, sync pulses, and color burst.
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Contrast Ratio |
This the ratio of the high light ouput level divided by the low light output level. In theory, the contrast ratio of the television system should be at least 100:1, if not 300:1. In reality, there are several limitations. In the CRT, light from adjacent elements containments the area of each element. Room ambient light will contaminate the light emitted from the CRT.
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dB |
Decibel. The standard unit used to express gain or loss of power. It indicates the logarithmic ratio of output power divided by input power. A power loss of 3dB is an attenuation of half of the original value.
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Distribution Amplifier |
A device that allows connection of one input source to multiple, isolated (buffered) output destinations such as monitors or projectors.
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DLP |
Digital Light Processing. In 1977 it was developed by Texas Instruments. A microchip used by projector subsystems to replace CRT technology. THey use an array of mirrors and memory cells. A digital image is stored in the memory, and then projected when light is reflected onto the mirrors.
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DVI |
Digital Visual Interface. The digital video connectivity standard that was developed by DDWG (Digital Display Work Group). This connection standard offers two different connectors: one with 24 pins that handles digital video signals only, and one with 29 pins that handles both digital and analog video.
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DVI-D |
DVI connector which supports digital signals only.
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DVI-I |
DVI connector which supports both digital and analog signals.
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Front Projection Screen |
A light-reflecting screen used when the image is projected from a source in front of the screen.
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Ghosting |
A shadowy or weak duplication of the original image. It can be the result of transmission conditions where secondary signals are created and then displayed earlier or later than the original signal. Ghosts can also be the result of burning an image on a screen or by a mirror.
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HDTV |
High Definition Television. HDTV refers to a complete product/system with the following minimum performance attributes: a receiver that receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format wiht active vertiacal scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher; aspect ratio capabilities for displaying a 16:9 image; receives and reprduces, and/or outputs Dolby Digital audio.
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Hot Spot |
Commonly seen on high-gain screens and screens diesigned for slide or movie projection, a hot spot is a circular area where the image is brighter than the rest of the screen. The hot spot is always located along the line of sight, and "moves" with the line of sight.
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Interlacing |
A video frame is made up of two fields. interlacing is the process of scanning the picture onto a video screen whereby the lines of one scanned field fall evenly between the lines of the preceding field.
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Keystone Effect |
A distorted picture where one edge is not the same dimension as the opposite edge, producing a tapered, or wedge shape. Typically this results when the image is projected to the screen at an angle.
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LAN |
Local Area Network. A local area network is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building).
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LCD |
Liquid Crystal Display. A panel that utilizes two transparent sheets of polarizing material with a liquid containing rod-shaped crystals between them. When a current is applied to specific pixel-like areas, those crystals align to create dark images. The dark areas are combined with light areas to create text and images on the panel. LCD panels do not emit light but are often back-lit or side-lit for better viewing.
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LCD Projector |
Utilizing the LCD technique, these projectors separate the red, green, and blue information to three different LCD panels. Since LCD panels do not produce color, the appropriate colored light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen.
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Loop-through |
A feature that allows the video signal to be passed through a device relatively unprocessed and sent to a local monitor or other device. The loop-through is separate from the circuits that process a signal for output to the main presentation or recording devices.
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Lumen |
A unit of measure for the amount of light emitted by a source. 0.98 Ft-c (foot-candles) of light covering a surface of 1 square foot.
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Non-interlaced |
Also called progressive scan. A method by which all the video scan lines are presented on the screen in one pass instead of two.
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PAL |
Phase Alternate Line. A television standard in which the phase of the color carrier is alternated from line to line. It takes four full pictures for the color-to-horizontal phase relationship to return to the reference point. This alternation helps cancel out phase errors.
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PAL-M |
Brazilian version of PAL. This is a broadcast standard with 525 lines and 60 fields per second.
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Pixel |
Picture element. A pixel is a single point in a graphic image or screen. Pixels are arranged in rows and columns.
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Pixel Resolution |
In computer graphics and video images, the pixel resolution is the number or pixels in the display. For example, a picture with 1,024x768 pixels is much sharbper, or has higher resolution, than a picture with 640x480 pixels. The total number of pixels is the product of these two numbers.
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Plenum Cable |
Cable having a covering (jacket) that meets UL specifications for resistance to fire.
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Progressive Scan |
See Non-interlaced.
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RCA Plug |
A connector type most often used with line level audio signals and composite video.
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Rear Projection Screen |
A translucent screen with a special coating that allows an image to be projected through the screen from the rear, instead of from the front.
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Rear Screen Projection |
A presentation method in which the image is projected through a translucent screen toward the audience.
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Resolution |
The density of lines or dots that make up an image. Resolution determines the detail and quality in the image. A measure of the ability of a camera or video system to reproduce detail, or the amount of detail that can be seen in an image. Resolution is often expressed as a number of pixels, but more correctly, it si the bandwidth. A sharp, clear picture has high resolution.
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RGB |
Red, green, blue. The chroma information in a video signal. The basic components of the color television system. They are also the primary colors of light in the additive color process.
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RGBHV |
Red, green, blue, horizontal, and vertical sync. A five-wire signal where the red, green, and blue video signals, as well as the horizontal and vertical sync signals are on its own conductor.
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S-Video |
A composite video signal separated into the luma ("Y" is for luma, or black and white information; brightness) and chroma ("C" is an abbreviation for chroam, or color information).
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Scaler |
A device that takes a standard video signal, decodes it, and uses advanced digital signal processing technology to scale the image to the optimal or native resolution of a display device.
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Scaling |
Scaling is changing the size of an image without changing its shape. Scaling may be required when the image size does not fit the display device. An example of scaling down would be to take a 640x480 resolution TV image and disply it as a smaller picture on the same screen so that multible pictures can be shown at the same time (such as picture in picture). If the original image is scaled down to a resolution of 320x240, this is 1/4 the original size, allowing four pictures to be shown on the same screen at the same time. An example of scaling up would be to take a lower resolution image (800x600 = 480,000 pixels) and display it on a higher resolution (1024x760 = 786,432 pixels) device. The number of pixels is the product of the two numbers. This means that pixels must be created. There are many different methods for image scaling, and some produce better resuilts than others.
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Serial Port |
An input/output connection on the computer that allows it to communicate with other devices in a serial fashion-data bits flowing on a single pair of wires. The serial port is used with RS-232 protocol.
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SVGA |
Super Video Graphics Array. A term used to denote resolutions higher than VGA (640x480). SVGA computer graphics cards have a resolution of 800x600 (480,000 pixels) but may be able to ouput resolutions of up to 1280x1024 and 16 million colors.
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SXGA |
Super Extended Graphics Array. A graphics standard with a resolution of 1280x1024 (1,310,720 pixels).
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Throw |
The distance from the projector lens to screen.
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USB |
Universal Serial Bus. USB was developed by seven PC and telecom industry leaders (Compaq, DEC, IBM, INtel, Microsoft, NEC, and Northern Telecom). The goal was easy plug-and-play expansiion outside the box, requiring no additional circuit cards. Up to 127 external computer devices may be added through a USB hub, which may be conveniently located in a keyboard or monitor. USB devices can be attaced/detached without removing computer power. The number of devices being designed for USB continues to grow, from keyboards, mice, and printers to scanners, digital cameras, and ZIP drives.
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UXGA |
Ultra Extended Graphic Array. 1600x1200. A UXXGA display has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector.
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VAR |
Value Added Re-seller. A party who purchases sells producs and adds support, service, know-how and other poducts and sells it as a complete package.
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VGA |
Video Graphics Array. Introduced by IBM in 1987, VGA is an analog signal with TTL level separate horizontal and vertical sync. The video outputs to a 15-pin HD connector and has a horizontal scan frequency of 31.5 kHz and vertical frequency of 70 Hz (mode 1,2) and 60 Hz (mode 3). The signal is non-interlaced in modes 1,2,3 and interlaced when using the 8541/Z card (35.5 kHz, 86 Hz) in mode 4. It has a pixel by line resolution of 640x480 with a color palette of 16/256,000.
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Videoconferencing |
Conducting a live conference between two or more locations using video cameras, microphones, and video monitors. The participants can be seen as well as heard.
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WSXGA |
WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as 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.
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WXGA |
WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as 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 verical pixels, respectively, that are used to compose the image delivered by the projector.
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XGA |
eXtended Graphics Array card. IBM's graphics standard that includes VGA and extended resolutions up to 1024x768 (interlaced 35 kHz). This card uses a 15-pin HD VGA-style connector.
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