Glossary

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Above Finished Floor (AFF)

This is an acronym commonly used in dimensioning. If you see a note saying 8'-0” AFF, it means that whatever is being referenced is 8 feet and zero inches above the surface of the finished floor (whatever you walk on, e.g. the surface of the tile, not the underlay) in that room.

Additive Color Process for Video Projection

Also called “RGB.” A color generation process used in video that combines red, green, and blue to make all colors. All three colors (red, green, and blue) at 100% combine to make white on a video screen; the absence of all three colors (0%) makes black. Also see “Subtractive color process (CMYK).”

ALR Screen

An ALR screen selectively reflects light back to the audience. This effect is achieved by positioning the projector and screen in such a way that the projector's light is bounced towards the audience, while the other, ambient light in the room is reflected back in some other direction out of the view of the audience. ALR screens only work if the ambient lighting is NOT hitting the screen from the same direction the projector.

ALRV

Ambient Light Rejection Value. (ALRV)   A test procedure measuring the percentage amount of an ambient light source placed at 45 degrees off a screen's viewing axis that is returned to the viewer's seating position at zero degrees on screen axis. The lower the number, the better the screen's ability to reject ambient light.

Ambient Light

The light surrounding an environment or subject. Also called available light, existing light measured in foot candles.

Anamorphic Lens

A type of lens or adapter designed to produce a widescreen image from a condensed image on the film. Trademarked anamorphic systems include CinemaScope, VistaVision, and Panavision.

Anamorphic DVD

A DVD with a widescreen video image that has been horizontally squeezed to fit into a standard video frame, resulting in an image with higher resolution than letter boxing can produce. Anamorphic DVDs are designed for optimal display on 16:9 widescreen displays or video scalers with an anamorphic squeeze mode.

ANSI Lumen

The common unit of measurement for the light output of a projector, as measured by ANSI, the American National Standards Institute. The higher the ANSI lumen rating, the brighter the projector. In general, there needs to be about a 30% differential in the ANSI lumen rating before the human eye can really notice an appreciable difference in brightness when two projectors are shown side by side. Determining the lumen output for a given application depends on five factors, (1) the level of ambient room light (2) the size of the audience, (3) the size of the projected image, (4) the quality of the projection screen, and (5) the amount of detail in the presentation material. See “Lumen.”

American National Standards Institute (ANSI)

ANSI is a private, non-profit organization that administers and coordinates the voluntary standardization and conformity assessment system in the US.

Aperture

The opening, usually an adjustable iris, that controls the amount of light passing through a lens. In motion picture cameras, the mask opening that defines the area of each frame exposed. In motion picture projectors, the mask opening that defines the area of each frame projected.

Aspect Ratio

The relationship of the horizontal dimension to the vertical dimension of an image. 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.

Bandwidth

A range or band of frequencies. Bandwidth often implies consistency of other parameters, such as amplitude or phase, in addition to defining the frequency range. In reality, a specification for bandwidth is meaningless without additional qualifying information.

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.

Brightness Ratio

The difference between the lightest (whitest) and darkest (blackest) areas in an image. The wider the brightness ratio, the wider the contrast ratio.

Candela

Derived from the word “candle” and denoted by the symbol “cd”, the candela is the standard unit of light intensity. One candela is roughly equal to the amount of light, in any direction, from the flame of a candle. The luminance of a light source is often expressed in candelas per square meter (cd/m2).

CIE Chromaticity Diagram

This is an international standard for primary colors established in 1931. It allows all other colors to be defined as weighted sum of the three "primary" colors. The CIE system characterizes colors by a luminance parameter Y and two, color coordinates x and y which specify the point on the chromaticity diagram.

Color Black

The NTSC standard for black, which is 8% gray. Computer black, the absence of all of the color primaries, is referred to as superblack and is used for matting or keying in video effects. Superblack does not render well to video. Instead of appearing black, it has a light grayappearance. Color black will appear blacker on video than superblack.

Collimation

A process whereby a beam of light is provided where all the rays generated or employed are traveling in approximately the same direction across the cross-section of the beam. 

Colorspace

A range of colors can be created by the primary colors of pigment and these colors then define a specific color space. Color space, also known as the color model (or color system), is an abstract mathematical model which simply describes the range of colors as tuples of numbers, typically as 3 or 4 values or color components (e.g. RGB). Basically speaking, color space is an elaboration of the coordinate system and sub-space. Each color in the system is represented by a single dot.

Color Temperature

The color quality, expressed in degrees Kelvin (K), of a light source. The higher the color temperature, the bluer the light. The lower the temperature, the redder the light. Benchmar color temperatures for the A/V industry include 5000° K (a comparatively “warm” or reddish color temperature, favored for pleasing video reproduction); 6500° K (D65, the reference color for accurate color reproduction); and 9000° K (a comparatively “cold” or bluish color temperature, favored for graphics and other high-contrast image reproduction).

Contrast

The range of light and dark values in a picture, or the ratio between the maximum and the minimum brightness values. Low contrast is shown mainly as shades of gray, while high contrast is shown as blacks and whites with very little gray. It is also the name of a TV monitor adjustment, which increases or decreases the level of contrast of a displayed picture. Also called “white level.”

Contrast range

The range of grays in a video image.

Contrast ratio

The ratio of the high light output level divided by the low light output level. Room ambient light will contaminate the light emitted from the display. Well-controlled viewing conditions should yield a practical contrast ratio of 30:1 to 50:1.

Convergence

The alignment of the red, green, and blue video projected onto a screen when the lines produced by the three color sources appear to form one clearly focused white line. The point at which the light from each of the three lenses aligns so the perceived single image is clearly focused. Lack of convergence is a video problem when the displayed image appears to be outlined by red, green, or blue because of misaligned colors.

DCI

Digital Cinema Initiatives, LLC (DCI) is a joint venture of major motion picture studios, formed to establish a standard architecture for digital cinema systems. Digital cinema refers to the use of digital technology to distribute or project motion pictures. A digital movie can be distributed to cinemas in a number of ways: over the Internet or dedicated satellite links or by sending hard drives or optical discs such as Blu-ray discs.

Digital movies are projected using a digital projector instead of a conventional film projector. Digital cinema is distinct from high-definition television and does not use television or high-definition video standards, aspect ratios, or frame rates. In digital cinema, resolutions are represented by the horizontal pixel count, usually 2K (2048×1080 or 2.2 megapixels) or 4K (4096×2160 or 8.8 megapixels).

Digital Keystone Correction

Digital keystone correction manipulates the projected image vertically and/or horizontally so that you can get it as close to appearing as an even rectangle as possible. It is performed digitally before the image passes through the lens, and is accessed by projector's onscreen menu function, or via a dedicated control button on the projector or remote control.

D-ILA Projection™

Direct Drive Image Light Amplifier. The D-ILA is a device based on the Image Light Amplifier or ILA developed by Hughes-JVC Technology Corporation. The D-ILA technology is a reflective liquid crystal modulator whereby electronic signals are addressed directly to the device. The D-ILA device has an X-Y matrix of pixels configured on a C-MOS single crystal silicon substrate mounted behind the liquid crystal layer using a planar process that is standard in Integrated Circuit technology.

DLP Projection

Digital Light Processing. An imaging technology for video projection developed by Texas Instruments based on the modulation of light reflected from mirror elements known as Micromirrors. Each pixel is represented by its own Micromirror which mechanically tilts in accordance to the extent of light reflected toward or away from the screen. A matrix of Micromirrors comprising the video image is situated on a microchip, or DMD (Digital Micromirror Device). DLP is implemented as a three-chip configuration (one DMD for each of the RGB colors), or as a one-chip configuration (R, G, and B are sequentially processed by a single DMD via a color wheel).

Diffuse, Diffusion

A diffuse surface is characterized by scattering of the incident light into many directions in the hemisphere before the surface. Examples are paper, matte paints, etc. A Lambertian surface is a perfect diffuser (it has the same luminance independent of the viewing direction—see “Lambertian”). Diffusion is the process of scattering light in directions away from directed ray (in transmission) or from the specular direction (in reflection).

Dispersion of Light

Colors are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet. The separation of visible light into its different colors is known as dispersio

Edge Blending

The use of multiple projectors with overlapping images to create a single, seamless vista on one screen.

 

Flat Field

A solid field of color used to calibrate monitors and projectors. A full, white flat field is typically used to evaluate the uniformity of a projected image.

First Surface Mirror

The front of a mirror. In mirrors intended for A/V applications, the first surface is coated with a reflective material to prevent double images (ghosting).

Fixed Frame Screen

Fixed screens are permanently tensioned screens that provide a contemporary, theatre-like appearance wherever a permanently mounted front or rear projection screen is required. The viewing surface is flat facilitating high picture quality.

FL

Focal Length. The distance between the center of a lens and the point where the image comes into focus. In projection, a shorter focal length yields a larger image on the screen for any given projection distance.

Focus

To adjust a lens to make the image appear sharp and well defined. The best possible resolution of an image, showing the image to be sharp and well defined.

Footcandle

A unit of illumination equivalent to the illumination produced by a source of one candle at a distance of one foot. Equal to one lumen incident to one square foot.

Footlambert

A unit of luminance (photometric brightness). The footlambert describes the luminance of a surface that emits or reflects one lumen per square foot; it is the luminance of a perfectly reflecting surface under an illumination of one footcandle. One footlambert equals 0.3183 candles per square foot.

Front Projection Screen

A light-reflecting screen used when the image is projected from a source in front of the screen. Also see “Rear projection screen.”

Front Screen Projection

To project an image from the audience’s side of a light-reflecting screen.

Gain (screen)

Gain is a measurement of the reflectivity of any screen or projection surface. The gain number represents a ratio of the light that is reflected from the screen as compared to the light reflected from a standard white (magnesium oxide) board. Therefore, a screen with a gain of 1.0 will reflect the same amount of light as that from a white board. A screen rated at 1.5 gain will reflect 50% more light as that from a white board, whereas a gray screen with an 0.8 rating will reflect 80% of the light from a white board.

Gamut

See colorspace

Grayscale

Grayscale is a range of shades of gray without apparent color. The darkest possible shade is black, which is the total absence of transmitted or reflected light. The lightest possible shade is white, the total transmission or reflection of light at all visible wavelengths. Intermediate shades of gray are represented by equal brightness levels of the three primary colors (red, green and blue) for transmitted light, or equal amounts of the three primary pigments (cyan, magenta and yellow) for reflected light.

Gray Screen

Gray screens or high contrast screens boost contrast on digital projectors in viewing rooms that are not entirely dark. The gray screen absorbs ambient light that strikes it better than a white screen does. In so doing the black level on the screen is maintained. If the projector has ample lumen output, whites remain white while blacks are maintained at a deeper black. The net effect is to increase the contrast range of the image on the screen.

Half Gain (screen)

Half Gain is the standard used to measure the brightness performance of a projection screen when the viewer is observing the screen from an extreme angle. A projection screen’s peak brightness occurs when the viewer is perpendicular to the center of the screen. As the viewer moves to the side, away from the center of the screen, the brightness of the image will decline. When the brightness drop-off reaches

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 with active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher; aspect ratio capabilities for displaying a 16:9 image; receives and reproduces, and/or outputs Dolby Digital audio. 

High Dynamic Rate (HDR)

It provides better contrast, greater brightness levels and a wider color space in order to make your display images look that more like real life. Your eyes can perceive brighter whites and darker blacks – greater dynamic range – than traditional formats. HDR content preserves details in the darkest and brightest areas of a picture that are lost using old standards such as Rec.709. It also allows for more natural, true-to-life colors that are closer to how we see them in real life.

 

Hot Spot

Commonly seen on high-gain screens and screens designed 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.

ILA Projection®

Image Light Amplifier. Used in their large screen projectors, a Hughes-JVC device that uses low-intensity images to modulate high-intensity light through a liquid crystal layer.

Illuminance

The light density (the luminous flux divided by area) shining onto a surface. This is the specification that measures how bright a screen is lit by a projector or ambient light. The unit is lux. 1 lux = 1 lumen/m2.

InfoComm ANSI Standard-DISCAS

Display Image Size for 2D Content in Audiovisual Systems (DISCAS) established a standard practice for calculating image size to viewing distance based on visual acuity.

Incident Light Meter

Incident light meters measure the amount of light falling on a subject. The incident meter is aimed at the light source and measures the light source falling directly on an object and is not influenced by the reflectance of the object. For more precise measurements, incident meters are also used to measure various levels of light from multiple sources falling on separate parts of the environment.

Interchangeable Lens

Interchangeable lenses are lenses that can be mounted on a projector and swapped out for other lenses. Unlike fixed lenses, which are built into projectors, interchangeable lenses provide the user with a wider choice of projection capabilities.

Kelvin

An absolute scale of temperature measurement typically used to describe the color of light, expressed in “degrees Kelvin.” The lower the number, the “warmer” or redder the color of the light; a higher number indicates a “colder”, or bluer, light source. Also see “Color Temperature.”

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. In stone buildings, the tapered stone at the top of an arch is the key that prevents the arch from falling.

Lace and Grommet Screen

Large, permanently tensioned screen. Furnished with reinforced webbing on all four sides and grommets on 4” to 6" centers. The screens attach to frames with lacing cords, springs or shock cords. Frames available in wood, aluminum or steel, for wall or suspended mounting.

Lambertian Reflectance

If a surface exhibits Lambertian reflectance, light falling on it is scattered such that the apparent brightness of the surface to an observer is the same regardless of the observer's angle of view. 

Lambert

A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 footcandles per square centimeter.

Lens Shift

Lens shift is the ability to move the projected image up or down, left or right, while keeping the projector stationary. It may be mechanical by moving the lens or digital in nature by processing the image for movement.

LCD Projection

Utilizing LCD panel technology, 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.

LCoS Projection

Liquid Crystal on Silicon. This is a reflective display technology where one glass substrate is attached to a silicon chip which is coated with crystals. The chip contains the control circuitry.

LED Display

An LED display is a direct view display, which uses an array of light-emitting diodes as pixels to show video. Their brightness allows them to be used outdoors in store signs and billboards, and in recent years they have also become commonly used indoors with finer pitch displays.

Lenticular Screen

A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. It must be held very flat to avoid hot spots. A large series of parallel lenticulations cut vertically into the screen surface to improve horizontal dispersion.

Linearity

The ability of a display device to produce an object the same size anywhere on the screen. For example, poor linearity may show the same line of text one size when it is at the top of the screen but a different size when it is at the bottom of the screen.

Long Throw Projection Lens

Long throw projectors have telephoto lenses that can create a much larger picture from longer throw distances

Lumen

The unit of measure for light coming out of a light source, such as a projector. CRT projectors usually use a 10% white window pattern for measurement purposes, while LCD and DLP projectors use a 100% white window (ANSI standard). Also see “ANSI Lumens.”

Luminance

The light density coming out of a surface. This is the specification for measuring the brightness of a projection screen or a CRT monitor’s tube surface. The SI unit is “cd/m2” (candles per square meter). It is also called “nit” in the US system and “footlambert” in the English system. 1 footlambert = 3.426 cd/m2.

Masking

A masking system creates a sharp black border when an image is narrower or shorter than your screen. Use a mask to realize the sharpest possible image with multiple aspect ratios.

Matte White

A reflection property of a surface that diffuses the incident light in quasi-Lambertian manner, i.e., the surface appears approximately the same brightness from all directions and there are not highlights or distinct reflections of sources. Often the term “diffuse” is also used in this manner. We speak of diffuse white standards and matte white paint, both refer to the same kind of reflection, although when we speak of a diffuse white standard we generally mean a material that is as close to a Lambertian reflector as possible. 

Moiré

A pattern resulting from a combination of other patterns. In video, this is usually an undesirable pattern caused by an unwanted signal interfering with the desired signal. This may appear as a wavy motion.

Nits

The nit is a unit of visible-light intensity, commonly used to specify the brightness of a flat panel display or direct view LED display.  One nit is equivalent to one candela per square meter.

Pin Cushion

The inward or outward (curved) appearance of the edges of a display.

Projection

The process of presenting visual media by light transmitted through an optics system to a viewing screen.

Projection Lamp

A modern projector lamp is an ultra-high pressure mercury vapor ARC lamp. Projector lamps are categorized as either metal halide lamps or ultra-high pressure mercury vapor lamps. Philips has trademarked the name "UHP lamp" for their projector lamps.

 

Rear Projection

Allows an image to be projected through the screen from the rear, instead of from the front. Also see “Front projection screen.”

Rear Screen Projection

A presentation method in which the image is projected through a translucent screen toward the audience.

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, video system and/or projection screen 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 is the bandwidth. A sharp, clear picture has high resolution.

Screen Gain

Screen gain is a measurement of the reflectivity of a screen or projection surface. The gain number represents a ratio of the light that is reflected from the screen as compared to the light reflected from a standard white (magnesium oxide) target. Therefore, a screen with a gain of 1.0 will reflect the same amount of light as that from a white reference target. A screen rated at 1.5 gain will reflect 50% more light as that from a white reference target, whereas a gray screen with a 0.8 rating will reflect 80% of the light from a white reference target.

Screen Half Gain Viewing Angle

A projection screen's peak brightness is when the viewer is directly in front and perpendicular to the center of the screen. This is referred to as Peak Gain at Zero Degrees Viewing Axis. As the viewer moves out to the side of the center of the screen axis, the brightness of the projected image will drop off. The screen's half gain (or half brightness) viewing angle specification is determined when the brightness drop off angle reaches 50 percent of peak gain,

SMPTE Color Bars

Society of Motion Picture and Television Engineers color bars is a television test pattern used for the NTSC video standard. Comparing this pattern as received to the known standard gives video engineers an indication of how an NTSC video signal has been altered by recording or transmission and what adjustments must be made to bring it back to specification. The pattern is also used for setting a television monitor or receiver to reproduce NTSC chrominance and luminance information correctly

Solid State Illumination

Replaces a traditional projection lamp with an LED array. LED and laser array, laser phosphor array (aka hybrid light source) or a pure RGB laser light source.

Video Projector

A device that projects a video image onto a presentation surface.

Wavelength

The distance from one peak to the next between identical points in adjacent waves of electromagnetic signals propagated in space or along a wire. Wavelength is usually specified in meters, centimeters, or millimeters. In the case of infrared, visible light, ultraviolet, and gamma radiation, the wavelength is usually specified in nanometers (10-9 meter) or Angstroms (10-10 meter). Wavelength is inversely related to frequency. The higher the frequency of the signal, the shorter the wavelength.

White Level

In television, the signal level that corresponds to the maximum picture brightness. The white level is set by the contrast control.

Zoom

A term used with video displays devices related to the ability to change the view anywhere between near and far. Definitions for near and far vary from one device to another.

Short Throw Projection Lens

Short throw projectors have lenses that can create a much larger picture from shorter throw distances

Spot Photometer

A photometer that measures the intensity of light received within a cone of small angle, usually 2° or less

Spot Meter

See spot photometer

SMPTE

The Society of Motion Picture and Television Engineers (SMPTE) is an international professional association, based in the United States of America, of engineers working in the motion imaging industries. An internationally recognized standards organization, SMPTE has more than 600 Standards for television production, filmmaking, digital cinema, audio recording, information technology, and medical imaging.

Snapper Screen

A fixed frame screen that uses snap fasteners to attach to the square tube frame.

Tab Tension Screen

Tabs containing tensioning wires are located on each side of the screen and ensures a smooth and completely flat screen surface.

Throw

When projector manufacturers talk about the throw capabilities of a projector, what they’re really referring to is the amount of distance you’ll need to “throw” an image between the projector itself and the screen to get the display size you desire.

Ultra-Short Throw Lenses

Ultra-short throw projectors, which can create an image of up to 100″ from a mere 15″ away.

Uniformity

This refers to the consistency of brightness over the entire image. For example, if a projector has a uniformity of 90%, and it is projecting a pure white (or single color) image on the entire screen there will be no more than 10% variation in intensity across the entire screen. Better quality projectors have higher % of Uniformity, and therefore produce a more accurate image.

Viewing Angle

In displays, viewing angle is the maximum angle at which a display can be viewed with acceptable visual performance. In a technical context, this angular range is called viewing cone defined by a multitude of viewing directions. Many manufacturers of projection screens thus define the viewing angle as the angle at which the luminance of the image is exactly half of the maximum.

Zoom Lens

A lens allowing a projector to change smoothly from a telephoto to a close-up or vice versa by varying the focal length.

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