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).”
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.
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.
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.
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.
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.
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.
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.
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.
The difference between the lightest (whitest) and darkest (blackest) areas in an image. The wider the brightness ratio, the wider the contrast ratio.
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).
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.
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.
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).
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.”
The range of grays in a video image.
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.
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.
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.
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).
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).
The use of multiple projectors with overlapping images to create a single, seamless vista on one screen.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.”
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.
A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 footcandles per square centimeter.
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.
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.
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.
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.
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.
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.”
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.
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.
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.
The inward or outward (curved) appearance of the edges of a display.
The process of presenting visual media by light transmitted through an optics system to a viewing screen.
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.
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 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,
A device that projects a video image onto a presentation surface.
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.
In television, the signal level that corresponds to the maximum picture brightness. The white level is set by the contrast control.
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.