Glossary » D

Digital to Analogue Converter. The signal process whereby a digital signal is converted to analogue, such as a graphics card might use when connected to an analogue monitor.

Discrete Cosine Transformation. The algorithm used for many data compression techniques including JPEG and MPEG2.

The act of removing magnetic fields that have built up inside a CRT. To prevent these fields from distorting the image an internal coil degausses them, either when the monitor is turned on or when a dedicated button/option is selected.

Depth cueing lowers the intensity of an object as it moves away from the viewpoint.

Range of distance within which objects in a picture appear sharp and in focus. Closing the aperture of a lens by choosing a larger “f-number” will increase its depth of field and vice versa. Note that wide angle lenses have broader inherent depth of field ranges than long focal length lenses.

Dynamic Host Configuration Protocol - A system used to assign IP addresses dynamically on a network.

This is the diagonal measurement of a CRT before it is housed inside its chassis and is not the viewable diagonal. Often quoted by manufacturers to categorise monitor sizes. For example, a monitor may have 19in diagonal linear measurement, but a viewable diagonal of around 18in. See viewable diagonal.

Available from www.DisplayMate.com, this is widely accepted as the de-facto software package used for testing monitors. A series of test screens with full descriptions, allow you to assess image quality and performance.

A commonly used transition effect that gradually superimposes the image of the second clip onto the first until only the second clip can be seen.

A codec that uses a proprietary version of MPEG4 compression to produce high-quality video with a comparatively small data rate.

Also known as AC-3. A multi-channel sound format where five speakers and a sub woofer are fed with individual sound elements to create a positional audio effect.

Denial of Service. A type of hacker attack on a network that attempts to flood it with useless traffic that exploits limitations in the network protocols. The aim is simply to bring the network to its knees. Distributed (DDoS) attacks target large web sites and use many private PCs that have been hacked to launch the attacks.

Applicable to shadow mask CRTs, this is the distance (in mm) between the centres of two phosphor dots of the same colour from neighbouring phosphor triads. The smaller the distance, the smaller the dot pitch will be, generally resulting in a sharper and finer picture. This should be measured between diagonally adjacent phosphor triads although some monitor manufacturers now quote horizontal dot pitch in order to produce a lower number.

Dot Product 3. This is a mathematically accurate form of bump mapping. Like EMBM, Dot3 bump mapping uses a special texture known as a bump map to specify the look of the base texture but unlike EMBM, Dot3 then takes vector information from the individual pixels in the base texture to calculate their angle and uses this and the vector information contained in the bump map to accurately calculate the way light interacts with that pixel. This effect can give a surface a very complex appearance.

This is the process of using two segments of graphics memory as frame buffers. One frame buffer, usually known as a primary surface buffer, holds a completed frame ready to be sent to your monitor while the other, usually referred to as a “back buffer” contains the frame that is currently being worked on. See also Triple Buffering.

Display Power Management System. A standard that defines four power levels namely, Normal, Standby, Suspend and Off. These can be described as follows: Normal is the full power state; Standby occurs when the horizontal sync signal is off and the vertical sync is on and when the RGB guns are off, but the power is on and the cathode is energised; Suspend occurs when the horizontal sync signal is on and the vertical sync is off and when the RGB guns and the power are off, and the cathode remains energised; Off is where everything is off, apart from some circuitry that monitors for horizontal or vertical sync signals in order to reactivate the power on state. The idea is to minimise power consumption.

Digital Print Order Format. Standard for describing where images are stored on a memory card and means by which a user can mark specific pictures for later printing.

The (usually minimum) size of a drop of ink an ink-jet printer can produce. Measured in picolitres (pl), 10-12 litre.

This connector carries the analogue video signals to a monitor, and usually consists of 15 pins that correspond to a different wire or signal. Head on, the ‘D’-shaped raised shield gives it it’s name. Also known as a DB15 cable.

AMD’s budget range of CPUs, usually a cut-down version of the Athlon.

Digital Video (also known as DV25). A video standard that with a data rate of 25Mbps and a compression ratio of 5.1. Used by most MiniDV camcorders.

The MPEG2 based video used by DVD camcorders from Hitachi, Sony and Panasonic.

This is a relatively new interface designed by the Digital Display Working Group (DDWG). Two main configurations exist: DVI-D for digital signals only, and DVI-I (integrated) for both analogue and digital signals. The majority of graphics cards use DVI-I ports and can be coupled with an LCD that has a DVI-D or DVI-I port for a pure digital-to-digital direct signal. If your graphics card only has a D-SUB port, then you need an analogue to DVI cable or a D-SUB-to-DVI converter (dongle) and an LCD monitor with a DVI-I port. In this case, you’re monitor still has to convert the analogue signal into a digital one with a resulting loss in quality.

As the electrons beams are scanned from left to right, the distance the electrons have to travel changes. In order for the beams’ spot sizes to remain focused, circuitry in the CRT constantly (and dynamically) adjusts the strength of the electromagnet fields to compensate.