Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
Dequantization – The process of rescaling the quantized discrete cosine
transform coefficients after their representation in the bit stream has been
decoded and before they are presented to the inverse DCT
Deserializer – A device that converts serial digital information to parallel.
Desk Top Video (DTV) – Use of a desktop computer for video production.
Detail – Refers to the most minute elements in a picture which are distinct
and recognizable. Similar to Definition or Resolution.
Development System – Microcomputer system with all the facilities
required for hardware and software development for a given microprocessor.
Generally consists of a microcomputer system, CRT display, printer,
mass storage (usually dual floppy-disk drivers), PROM programmer, and incircuit
emulator.
Device Driver – Software to enable a computer to access or control a
peripheral device, such as a printer.
DFD (Displaced Frame Difference) – Differential picture if there is
motion.
D-Frame – Frame coded according to an MPEG-1 mode which uses DC
coefficients only.
D/I (Drop and Insert) – A point in the transmission where portions of the
digital signal can be dropped out and/or inserted.
DII – Download Information Indication.
Diagnostics – A series of tests that check hardware components of a
system.
Diagonal Resolution – Amount of detail that can be perceived in a diagonal
direction. Although diagonal resolution is a consequence of horizontal
and vertical resolution, it is not automatically equivalent to them. In fact,
ordinary television systems usually provide about 40 percent more diagonal
resolution than horizontal or vertical. Many ATV schemes intentionally sacrifice
diagonal resolution in favor of some other characteristics (such as
improved horizontal or vertical resolution) on the theory that human vision
is less sensitive to diagonal resolution than to horizontal or vertical. There
is some evidence that diagonal resolution could be reduced to about 40
percent less than either horizontal or vertical (overall half of its NTSC value)
with no perceptible impairment. See also Resolution.
Diagonal Split – An unusual quad split feature found on Ampex switchers,
allowing diagonal or X-shaped divisions between sources, as opposed to
the traditional horizontal and vertical divisions.
Dialog Normalization Value – The dialog normalization value is a Dolby
Digital parameter that describes the long-term average dialog level of the
associated program. It may also describe the long-term average level of
programs that do not contain dialog, such as music. This level is specified
on an absolute scale ranging from –1 dBFS to –31 dBFS. Dolby Digital
decoders attenuate programs based on the dialog normalization value in
order to achieve uniform playback level.
DIB (Device Independent Bitmap) – A file format that represents bitmap
images in a device-independent manner. Bitmaps can be represented at 1,
4, and 8 bits-per-pixel with a palette containing colors representing 24
bits. Bitmaps can also be represented at 24 bits-per-pixel without a palette
in a run-length encoded format.
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Differential Gain – a) This nonlinear distortion is often referred to as “diff
gain” or “dG.” It is present if a signal’s chrominance gain is affected by
luminance levels. This amplitude distortion is a result of the system’s
inability to uniformly process the high-frequency chrominance signals at all
luminance levels. The amount of differential gain distortion is expressed in
percent. Since both attenuation and peaking of chrominance can occur in
the same signal, it is important to specify whether the maximum over all
amplitude difference or the maximum deviation from the blanking level
amplitude is being quoted. In general, the NTSC measurement standard
defines differential gain as the largest amplitude deviation between any two
levels, expressed as a percent of the largest chrominance amplitude. When
differential gain is present, color saturation has an unwarranted dependence
on luminance level. Color saturation is often improperly reproduced at
high luminance levels. The Modulated Ramp or Modulated Stair Step signals
can be used to test for differential gain. b) The amplitude change,
usually of the 3.6 MHz color subcarrier, introduced by the overall circuit,
measured in dB or percent, as the subcarrier is varied from blanking to
white level.
Differential Phase – a) This nonlinear distortion is often referred to as
“diff phase” or “dP.” It is present if a signal’s chrominance phase is affected
by the luminance level. It occurs because of the system’s inability to
uniformly process the high-frequency chrominance information at all luminance
levels. Diff Phase is expressed in degrees of subcarrier phase. The
subcarrier phase can be distorted such that the subcarrier phase is
advanced (lead or positive) or delayed (lag or negative) in relation to its
original position. In fact, over the period of a video line, the subcarrier
phase can be both advanced and delayed. For this reason, it is important
to specify whether “peak to peak diff phase” is being specified or “maximum
deviation from 0” in one direction or another. Normally the “peak to
peak diff phase” is given. dP distortions cause changes in hue when picture
brightness changes. Colors may not be properly reproduced, particularly
in high-luminance areas of the picture. b) The phase change of the
3.6 MHz color subcarrier introduced by the overall circuit, measured in
degrees, as the subcarrier is varied from blanking to white level.
Differential Pulse Code Modulation – DPCM is a source coding scheme
that was developed for encoding sources with memory. The reason for
using the DPCM structure is that for most sources of practical interest, the
variance of the prediction error is substantially smaller than that of the
source.
Differentiated Step Filter – A special filter sometimes also called a “diff
step” filter that is used to measure luminance nonlinearity. When this filter
is used with a luminance step waveform (see the waveform discussed in
the Luminance Nonlinearity discussion), each step on the waveform is
translated into a spike that is displayed on the waveform monitor. The
height of each spike translates into the height of the step so the amount of