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Glossary - Computer Monitors

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ACTIVE TIMING - The portion of the video signal that carries the actual video information.

APERTURE GRILLE MASK - Image made up of vertical groupings of red, blue, and green phosphor stripes instead of dots. Aperture grille monitors will have two barely visible wires going across the screen to help stabilize the image.

ASPECT RATIO - The ratio of a monitor's height to its width. Typical aspect ratio for a monitor is 4 to 3 , or 1.33. Example: 640/480 = 1.33

BANDWIDTH - Qualitative term describing the video amplifier's potential performance. The higher the pixel rate (or format number), the higher the bandwidth required of the video amplifier.

BARREL - An outward bowing of the picture. A condition in which colors appear to flow into unintended areas of the image.

BRIGHTNESS - Light output measures at the faceplate of the CRT, typically measured in foot-lamberts (F1). A minimum brightness level of 20F1 when viewing at full-page size is considered acceptable.

CHARACTER MATRIX - The total number of horizontal and vertical spaces required per character.

CONTRAST - The ratio between the maximum and the minimum luminance values of the display.

CONTRAST CONTROL - A manual control for a monitor that affects both luminance and contrast.

COLOR BALANCE - The ability of the monitor to show and maintain the same color when switching or varying the intensity of the screen.

CONVERGENCE - The ability of the electron beam to accurately hit the correct phosphor dot.

CRT - Abbreviation for cathode ray tube, also know as picture tube or screen.

DEGAUSSER - A device that removes unwanted magnetism from a monitor or the read/write head of a disk or tape drive.

DOT PITCH - The distance between one phosphor dot and the nearest dot of the same color in the line above or below.

FLICKER - Lit condition of the display caused by mismatch of phosphor and vertical refresh when the phosphor begins to decay prior to being refreshed, giving the display the appearance of "flashing"

FOCUS - Sharpness of a pixel or series of pixels on the CRT face plate. Also measured as the spot size.

FRAME - A single refresh of the entire screen as perceived by the viewer.

HIGH VOLTAGE REGULATION - Ability of the high voltage to respond to changes inn beam current. Good high voltage regulation means a stable display even when changing intensity levels.

HORIZONTAL SCAN FREQUENCY - The number of lines illuminated on a video screen in one second, or how long it takes to scan each of the horizontal lines that make up the display, measured in kilohertz (kHZ).

INTERLACED - Method of significantly increasing data densities at conventional horizontal scan rates.

MAGNETIC FIELD EFFECTS - Effect of magnetizing elements on screen. A steel cabinet, desk, bench, or even magnetic polarity of the earth may interfere with the picture tube's electron beams.

MPRŚ° - The Swedish National Board for Measurement and Testing (SWEDAC) requires that products sold in Sweden comply with a set of safety standards known as MPRŚ° ,which covers the levels of magnetic and electrical fields.

PERSISTENCE - Phosphor characteristic consisting of the ability to emit light after the excitation current of an electron beam is removed.

PHOSPHOR - Chemical compound that emits light while being excited by electrons.

PINCUSHION - An inward bowing hour glass shape of the video image. All monitors experience slight pincushion distortion. The manufacturer gives guidelines on the specifications for each model. The pincushion changes according to resolution and also according to the size of the image.

PIXEL - Short for picture element, a pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns.

PURITY - The ability of the electron beam to hit precisely the correct phosphor color dot. If a full page of red color were shown on the display, impurities would result in a purple or greenish color region. These impurities can occur if the shadow mask has been damaged or if the screen has become magnetized. Degaussing the screen may fix the problem.

REFRESH RATES - The number of times per second that a device is re-energized, such as a CRT. An ergonomic issue that is directly related to long term ease of use. A higher refresh rate translates into a more flicker-free display.

RESOLUTION - The number of pixel or dots per frame (DPI).

SHADOW MASK - A thin screen full of holes that adheres to back of a color CRT's viewing glass. The electron beam is aimed through the holes in the mask onto the phosphor dots.

SVGA - (SuperVGA) Enhancements to the VGA standard that increased resolution to 800 x 600 and beyond. The term may be used to refer to 800 x 600 resolution in general.

TILT - The angle of the viewable frame with respect to the horizontal plane. Tilt can vary depending on the monitor's orientation to the earth's magnetic poles. Monitor manufacturers orient and align their products in the eastern direction. When the monitor is facing a north/south direction, there may be a slight rotation of the image.

UNIFORMITY - Comparison of one area's brightness to that of an adjacent area. In general, the brightest part of the image will be in the center. Toward the edges, the intensity of image will vary in a non-linear function.

VERTICAL SCAN FREQUENCY - How many times per second the monitor can draw all the lines on an entire screen. A higher vertical frequency or refresh rate will produce fewer flickers.

VGA - (Video Graphics Array) The minimum standard for PC video display, which originated with IBM's PS/2 models in 1987.

XGA - (Extended Graphics Array) An IBM video display standard introduced in 1990 that extended VGA to 132-column text and interlaced 1024 x 768 x 256 resolution.