Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
black on TV monitors in a control room “dimly lighted.” This luminance ratio
specification has been formalized in SMPTE RP 166.
Black, Subjective, Scene – That fraction of the high-light luminance
required in a scene reproduced on a television display to convey the perception
of black. The luminance of subjective black on a CRT has been
studied by Lowry and Jarvis, who measured luminances on the original
scenes, and compared the subjective appearance on a CRT display, as
evaluated by viewing audiences. They found that the perception of black
depends on a great many factors both in the reproduced scene and in the
viewing conditions such as average scene reflection, luminance of areas
adjacent to the display, etc. In most situation, luminance levels of 1/40 to
1/60 of the highlight luminance produce the perception of black even
though the scene luminance range may reach 200:1 or more. It follows,
then, that a scene element that is perceived as black may not necessarily
be at reference-black level in a video signal.
Blacker-than-Black – The amplitude region of the composite video signal
below reference-black level in the direction of the synchronizing pulses.
Blanking – A video signal level below which no light should be emitted
from a TV screen (the level at which the screen is blanked); also, that portion
of the time that a video signal is transmitted when it is at or below
blanking. These time portions can be divided into a horizontal blanking
interval (HBI) and a vertical blanking interval (VBI). Since no picture information
is carried in either blanking interval in an NTSC signal, various ATV
schemes propose using them for carrying augmentation information, such
as higher quality sound or widescreen panel information. Potentially conflicting
with those schemes are other schemes that already use the blanking
intervals for descrambling codes, test transmission, time code, and test
and reference signals. Reducing the duration of the blanking intervals to
allow more picture information to be transmitted potentially conflicts with
the demands of the scanning circuitry of older TV sets. Sometimes this
conflict is said to be resolved by bezel coverage and overscanning.
Blanking (Picture) – The portion of the composite video signal whose
instantaneous amplitude makes the vertical and horizontal retrace invisible.
Blanking Adjustment – A technique proposed in some ATV schemes to
increase the VBI (and, sometimes, decrease the HBI) to deal with wide
aspect ratios. See also Burn.
Blanking Interval – The horizontal blanking interval is the time between
the end of one horizontal scanning line and the beginning of the next. The
vertical blanking interval is the time between the end of one video field and
the beginning of the next. Blanking occurs when a monitor’s electron beam
is positioned to start a new line or a new field. The blanking interval is
used to instantaneously reduce the beam’s amplitude so that the return
trace is invisible.
Blanking Level – a) Refers to the 0 IRE level which exists before and
after horizontal sync and during the vertical interval. This voltage level
allows the electron beam to be turned off while it is being repositioned
(retracing) across the face of the CRT into the position needed to start
tracing the next visible line. b) The level of the front and back porches of
the composite video signal. c) The level of a composite picture signal
which separates the range containing picture information from the range
20 www.tektronix.com/video_audio
containing synchronizing information. Note: This term should be used for
controls performing this function (IEEE 100).
Blanking Panel – A piece of black plastic attached to the front plastic
panel of the Indigo chassis that covers either the top or middle drive slot.
The blanking panel is removed after installing a drive in the slot that it was
covering.
Blanking Processor (Sync Proc) – A circuit on the video module which
strips blanking sync and burst from the program output of the switcher and
replaces it with blanking and sync from a reference source. This process
ensures that sync and blanking do not contain any unwanted timing shifts,
and the record VPR is always receiving constant relationships of sync,
blanking, and burst.
Blanking Stuffing – An ATV technique that adds information to blanking
areas that is supposed to be invisible to ordinary sets but can be used by
an ATV set for increased resolution and/or widescreen panels.
Blast Filter – A dense mesh screen on a microphone, which minimizes
overload caused by loud, close sounds.
Bleeding Whites – An overloading condition in which white areas appear
to flow irregularly into black areas.
Blink – A modification to a key to cause it to flash on and off. The speed
at which a key blinks.
Blitting – The process of using BitBLT to copy video data such as a
bitmap from one area in memory to another.
Block – An 8-row by 8-column matrix of pels, or 64 DCT coefficients
(source, quantized or dequantized). A block is the entity on which the DCT
operates. Please note, that the term “block” is used for both the actual picture
information, and the corresponding DCT coefficients. A block represents
luminance or chrominance information.
Block Matching – A method of motion estimation. A search for the picture
area that best matches a specific macro block of preceding and/or
subsequent pictures.
Blockiness – An artifact that refers to the tile-like appearance of a compressed
image where the 8x8 blocks have become visible due to a (too)
hard compression.
Blocking – a) Occurs in a multistage routing system when a destination
requests a source and finds that source unavailable. In a tie line system,
this means that a destination requests a tie line and receives a tie line
busy message, indicating that all tie lines are in use. b) Distortion of the
received image characterized by the appearance of an underlying block
encoding structure.
Blooming – This effect is sometimes called whiter-than-white. Blooming
occurs when the white voltage level is exceeded and screen objects
become fuzzy and large.
BLT (Block Transfer) – The process of moving blocks of data from one
place to another rather than a byte at a time in order to save processor
time and to expedite screen display in operations such as vertical rolling of
video.
Blue Aging – A tendency for blue phosphors to age more rapidly than red
or green. See also Phosphor Aging.