Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
constrained by the practical filters, sensors, phosphors, etc. employed in
order to achieve conformance to the defined primary colors of the specified
system. Similar matrix transformations compensate for the viewing conditions
such as a white point of the display different from the white point of
the original scene. d) Choosing and defining primary colors requires a balance
between a wide color gamut reproducing the largest number of
observable surface colors and the signal-to-noise penalties of colorimetric
transformations requiring larger matrix coefficients as the color gamut is
extended. e) There is no technical requirement that primary colors should
be chosen identical with filter or phosphor dominant wavelengths. The
matrix coefficients, however, increase in magnitude as the available display
primaries occupy a smaller and smaller portion of the color gamut. (Thus,
spectral color primaries, desirable for improved colorimetry, become
impractical for CRT displays.) f) Although a number of primary color sets
are theoretically interesting, CCIR, with international consensus, has established
the current technology and practice internationally that is based
(within measurement tolerances) upon the following: Red – x = 0.640, y =
0.330; Green – x = 0.300, y = 0.600; Blue – x = 0.150, y = 0.060.
g) SMPTE offers guidance for further studies in improving color rendition
by extending the color gamut. With regard to color gamut, it is felt that the
system should embrace a gamut at least as large as that represented by
the following primaries: Red – x = 0.670, y = 0.330; Green – x = 0.210,
y = 0.710; Blue – x = 0.150, y = 0.060.
Color, Subjective – Subtractive colorimetry achieves metameric matching
by removing portions of the spectrum from white light. The subtractive
counterparts to the additive color primaries are those which when removed
from white leave the red, green, and blue accordingly cyan, magenta, and
yellow. Combinations of these subtractive colors in various add mixtures
provide metameric matches to many colors. Subtractive color principles are
employed in all hard-copy color images and in light-valve systems such as
color transparencies, LCD panel display, motion-picture films, etc.
Colorimetry – a) Characteristics of color reproduction including the range
of colors that a television system can reproduce. Some ATV schemes call
for substantially different colorimetry (with a greater range) than NTSC’s.
b) The techniques for the measurement of color and for the interpretation
of the results of such computations. Note: The measurement of color is
made possible by the properties of the eye, and is based upon a set of
conventions.
Colorization – Special effect (also called paint) which colors a monochrome
or color image with artificial colors. This feature is found on both
the Digital Video Mixer and Video Equalizer.
Color-Matching Functions – a) The tristimulus values of monochromatic
stimuli of equal radiant power. The three values of a set of color-matching
functions at a given wavelength are called color-coefficients. The colormatching
functions may be used to calculate the tristimulus values of a
color stimulus from the color stimulus function. b) The tristimulus value per
unit wavelength interval and unit spectral radiant flux. c) A set of three
simultaneous equations used to transform a color specification from one
set of matching stimuli to another. Note: Color-matching functions adopted
by the CIE are tabulated as functions of wavelength throughout the spectrum
and are given in Section 13.5 of ANSI/IES RP16-1986.
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Comb Filter – A filter that can be used to separate luminance from
chrominance in the NTSC or PAL composite video systems. The figure
below shows a signal amplitude over frequency representation of the luminance
and chrominance information that makes up the composite video
signal. The peaks in gray are the chroma information at the color carrier
frequency. Note how the chroma information falls between the luminance
information that is in white. The comb filter is able to pass just energy
found in the chroma frequency areas and not the luminance energy. This
selective bandpass profile looks like the teeth of a comb and thus the
name comb filter. The comb filter has superior filtering capability when
compared to the chroma trap because the chroma trap acts more like a
notch filter.
Frequencies the Comb Filter
passes as chrominance information.
Combination Tone – A tone perceived by the ear which is equal in frequency
to the sum or difference of the frequencies of two loud tones that
differ by more than 50 Hz.
Combinational Logic – Circuit arrangement in which the output state is
determined only by the present states of two or more inputs. Also called
Combinatorial Logic.
Combiner – In digital picture manipulators, a device that controls the way
in which two or more channels work together. Under software control, it
determines the priority of channels (which picture appears in front and
which in back) and the types of transitions that can take place between
them.
Combo Box – In Microsoft Windows, a combination of a text and a list
box. You can either type the desired value or select it from the list.
Command Buttons – In Microsoft Windows, “button-shaped” symbols
that are “pressed” (“clicked on”/chosen) to perform the indicated action.
Comment Field – Field within an instruction that is reserved for comments.
Ignored by the compiler or the assembler when the program is converted
to machine code.
Common Carrier – Telecommunication company that provides communications
transmission services to the public.
Common Data Rate (CDR) – In the search for a single worldwide standard
for HDTV, one proposal is to establish a common data rate, to be
independent of line structure, frame rate, and sync/blanking.