Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
of bits required for transmission and may be either lossless or lossy.
b) Step-by-step procedure for the solution to a problem. First the problem
is stated and then an algorithm is devised for its solution.
Alias, Aliasing – Something other that what it appears to be. Stairsteps
on what should be a smooth diagonal line are an example of spatial alias.
Wagon wheels appearing to move backwards are an example of temporal
alias. Aliases are caused by sampling and can be reduced or eliminated by
pre-filtering, which can appear to be a blurring effect. Defects in the picture
typically caused by insufficient sampling (violation of the Nyquist sampling
rate) in the analog-to-digital conversion process or poor filtering of
digital video. Defects are typically seen as jaggies on diagonal lines and
twinkling or brightening in picture detail. Examples are: Temporal Aliasing –
such as rotating wagon wheel spokes appearing to rotate in the reverse
direction. Raster Scan Aliasing – such as sparkling or pulsing effects in
sharp horizontal lines. Stair-Stepping – stepped or jagged edges in diagonal
lines or the diagonal parts of a letter.
Alignment – Most commonly, Head Alignment, but also used to describe
the process of adjusting a recorder’s Bias and Equalization for optimum
results from a specific tape.
Alpha – See Alpha Channel and Alpha Mix.
Alpha Channel – The alpha channel is used to specify an alpha value for
each color pixel. The alpha value is used to control the blending, on a
pixel-by-pixel basis, of two images. Alpha typically has a normalized value
of 0 to 1. In a computer environment, the alpha values can be stored in
additional bit planes of frame-buffer memory. When you hear about 32-bit
frame buffers, what this really means is that there are 24 bits of color, 8
each for red, green, and blue, along with an 8-bit alpha channel. Also see
Alpha Mix.
new pixel = (alpha) (pixel A color) + 1 – alpha (pixel B color)
Alpha Mix – A way of combining two images. How the mixing is performed
is provided by the alpha channel. The little box that appears over
the left-hand shoulder of a news anchor is put there by an alpha mixer.
Wherever the pixels of the little box appear in the frame buffer, an alpha
number of “1” is put in the alpha channel. Wherever they don’t appear, an
alpha number of “0” is placed. When the alpha mixer sees a “1” coming
from the alpha channel, it displays the little box. Whenever it sees a “0,” it
displays the news anchor. Of course, it doesn’t matter if a “1” or a “0” is
used, but you get the point.
Alphanumeric – Set of all alphabetic and numeric characters.
ALU – See Arithmetic and Logic Unit.
AM – A form of modulation where the level of the baseband information
affects the level of the carrier. See Amplitude Modulation.
A-MAC – A MAC (Multiplexed Analog Component) with audio and data frequency
multiplexed before modulation. See also MAC.
Ambient Lighting – Light that emanates from no particular source, coming
from all directions with equal intensity.
Ambient Sound – A representative sample of background audio (such as
a refrigerator hum or crowd murmur) particular to a shooting location.
Ambient sound is gathered in the course of a production to aid the sound
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editor in making cuts or filling in spaces between dialog. Also called Room
Tone.
American Television and Communications – See ATC.
A-Mode Edit – An editing method where the footage is assembled in the
final scene order. Scene 1, scene 2, etc.
Amplitude – The height of a waveform above or below the zero line.
Amplitude Modulation – a) The process used for some radio (AM broadcast,
in North American audio service broadcast over 535 kHz-1705 kHz)
and television video transmission. A low-frequency (program) signal modulates
(changes) the amplitude of a high-frequency RF carrier signal (causing
it to deviate from its nominal base amplitude). The original program
signal is recovered (demodulated) at the receiver. This system is extensively
used in broadcast radio transmission because it is less prone to signal
interference and retains most of the original signal quality. In video, FM is
used in order to record high quality signals on videotape. b) The process
by which the amplitude of a high-frequency carrier is varied in proportion
to the signal of interest. In the PAL television system, AM is used to encode
the color information and to transmit the picture. Several different forms of
AM are differentiated by various methods of sideband filtering and carrier
suppression. Double sideband suppressed carrier is used to encode the
PAL color information, while the signal is transmitted with a large-carrier
vestigial sideband scheme.
Amplitude Non-Uniformity – A term used in connection with magnetic
tape testing and refers to the reproduced peak-to-peak voltage and its
variation from what was recorded.
Amplitude Versus Frequency Response – Refer to the Frequency
Response discussion.
AM-VSB (Amplitude Modulation with Vestigial Sideband) – The form
of modulation used in broadcast and cable television transmission. It is
more efficient than dual-sideband amplitude modulation and is easier to
implement than single-sideband amplitude modulation.
Analog – a) A continuous electrical signal that carries information in the
form of variable physical values, such as amplitude or frequency modulation.
b) A signal which moves through a continuous range of settings or
levels. c) An adjective describing any signal that varies continuously as
opposed to a digital signal that contains discrete levels representing the
binary digits 0 and 1. d) A signal that is an analogy of a physical process
and is continuously variable, rather than discrete. See also Digitization.
Analog Components – Video signals in which a continuously variable
voltage or current (rather than a set of digital numbers) represents a pixel.
Analog Interface – An interface between a display controller and a display
in which pixel colors are determined by the voltage levels on three
output lines (RGB). Theoretically, an unlimited number of colors can be supported
by this method (24 bits per pixel allows 16,777,216 colors). The
voltage level on any line varies between zero volts (for black) to about 700
millivolts (for maximum brightness).
Analog Monitor – A video monitor which accepts analog signals. Several
types of inputs are accepted by analog monitors: composite video, RGB &
sync, Y/C, YUV and any combination of these formats. The signals transmit-