Specifications

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A Digital Video Primer
Glossary
4:1:1 color: Nonbroadcast color-sampling system in which for every four samples of the luminance (Y)
component, one sample of each of the two chrominance components (Cr and Cb) are taken.
4:2:0 color: Color-sampling system used for PAL video in which for every four samples of the
luminance (Y) component, two samples of each of the two chrominance components (Cr and
Cb) are taken but, unlike 4:2:2 color, only on every other line of each eld.
4:2:2: color: Color-sampling system used for NTSC video in which for every four samples of the
luminance (Y) component, two samples of each of the two chrominance components (Cr and
Cb) are taken.
8-bit-per-channel color: Type of color representation that stores and transmits 8 bits of information
for each of the red, green, and blue (RGB) components. In computer terms, known as 24-bit color.
24-bit color: Type of color representation used by most computers. For each of the red, green,
and blue components, 8 bits of information are stored and transmitted—24 bits total. With these
24 bits of information, over a million dierent variations of color can be represented. In digital
video, known as 8-bit-per-channel color.
24P: A high-denition (1080 lines of vertical resolution), 24 fps, progressive-display video format.
AAF: e Advanced Authoring Format, which was developed to provide a common (open)
le format to allow content to be used by dierent multimedia authoring and post-produc-
tion soware applications. AAF is an open standard for the interchange of program content
(actual images, video and audio clips, and so forth.) and its associated metadata (ancillary
data that describes source location, timecode, transitions, and eects applied) across platforms
and between applications. Sometimes described as a super EDL solution, AAF is, essentially, a
wrapper technology that can carry either the content itself or merely links (pointers) to it, along
with relevant metadata. Although AAF les may contain the actual content, the emphasis of
this format (contrast with MXF) is the exchange of composition metadata (that is, the informa-
tion that describes how content is handled in a composition, rather than on the exchange of the
content itself).
Aliasing: e jaggy appearance of unltered angled lines. Aliasing is oen caused by sampling
frequencies too low to faithfully reproduce an image. ere are several types of aliasing that can
aect a video image including temporal aliasing (for example, wagon wheel spokes
apparently reversing) and raster scan aliasing (such as ickering eects on sharp horizontal
lines).
Alpha channel: Color in an RGB video image is stored in three color channels (see channel). An
image can also contain a matte (also known as a mask) stored in a fourth channel called the
alpha channel.
Analog: e principal feature of analog representations is that they are continuous. For example,
clocks with hands are analog—the hands move continuously around the clock face. As the min-
ute hand goes around, it not only touches the numbers 1 through 12, but also the innite number
of points in between. Similarly, our experience of the world, perceived in sight and sound, is
analog. We perceive innitely smooth gradations of light and shadow; innitely smooth modula-
tions of sound. Traditional (nondigital) video is analog.
Animatic: A limited animation used to work out lm or video sequences. It consists of artwork
shot on lm or videotape and edited to serve as an on-screen storyboard. Animatics are oen
used to plan out lm sequences without incurring the expense of the actual shoot.
Anti-aliasing: e manipulation of the edges of a digital image, graphic, or text to make them
appear smoother. On zoomed inspection, anti-aliased edges appear blurred, but at normal view-
ing distance, the apparent smoothing is dramatic. Anti-aliasing is important when working with
high-quality graphics for broadcast use.
Artifact: Visible degradations of an image resulting from any of a variety of processes. In digital
video, artifacts usually result from color compression and are most noticeable around sharply
contrasting color boundaries such as black next to white.