Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
Color Black – A composite video signal that produces a black screen
when viewed on a television receiver.
Color Burst – a) The portion of a color video signal that resides on the
backporch between the breezeway and the start of active video that contains
a sample of the color subcarrier used to add color to a signal. It is
used as a color synchronization signal to establish a reference for the color
information following it and is used by a color monitor to decode the color
portion of a video signal. The color burst acts as both amplitude and phase
reference for color hue and intensity. The color oscillator of a color television
receiver is phase locked to the color burst. b) A nine-cycle-NTSC
burst of color subcarrier which is imposed on blanking after sync. Color
burst serves as the reference for establishing the picture color.
Color Coordinate Transformation – Computation of the tristimulus values
of colors in terms of one set of primaries from the tristimulus values of
the same colors in another set of primaries. Note: This computation may be
performed electrically in a color television system.
Color Correction – a) A process by which the coloring in a television
image is altered or corrected electronically. Care must be taken to ensure
that the modified video does not exceed the limits of subsequent processing
or transmission systems. b) The adjustment of a color reproduction
process to improve the perceived-color conformity of the reproduction to
the original.
Color Decoder – A device that divides a video signal into its basic color
components. In TV and video, color decoding is used to derive signals
required by a video monitor from the composite or Y/c.a. signals. See
Chroma Demodulators.
Color Demodulator – See Chroma Demodulators.
Color Difference Signals – Signals used by color television systems to
convey color information (not luminance) in such a way that the signals go
to zero when there is no color in the picture. Color difference signal formats
include: R-Y and B-Y; I and Q; U and V; PR and PB . The figure below
shows general color difference waveforms along with the Y signal. The
color difference signals must first be converted in their RGB form before
they can recreate the picture. Refer to the RGB discussion to view what the
RGB version of the color bar signal looks like. The color difference signals
in the figure are centered around 0 volts, but this is only true for the
SMPTE/EBU N10 standard. The NTSC and M11 color difference standards
have the most negative portions of the color difference signals riding on a
voltage of 0 volts or close to it.
Color Edging – Spurious colors appearing along the edges of color pictures,
but that do not have a color relationship to the picture.
34 www.tektronix.com/video_audio
Y P B, B-Y, V or Q P R, R-Y, U or I
Color Encoder – Performs the reverse function of the chroma demodulator
in that it combines the two color difference signals into the single chroma
signal.
Color Frame – a) In NTSC color television, it takes four fields to complete
a color frame. In PAL, it takes eight fields. b) Polarity of the video frame.
Color frame must alternate polarity with each frame to keep the video signal
in phase.
Color Frame Timed – See the Color Framed discussion.
Color Framed – Two signals are said to be color framed at a switcher or
router when their field 1, line 10 events (field 1, line 7 in PAL) occur at the
same time at the input to the switcher or router. To prevent picture distortions
when changing signals at a switcher or router, the signals must be
color framed.
Color Gamut – In a system employing three color primaries to encode
image color, each primary can be located on a CIE chromaticity diagram
and these points connected as a plane figure. If the apexes are then connected
with an appropriate value on the white point axis, a so) id figure is
produced enclosing the color gamut for that system. (On the CIE chromaticity
diagrams, the points in x, y, z space approximate an inverted tetrahedron.
In u, v, w space, they become a somewhat irregular four-cornered
solid.) Colors within the color gamut solid volume can be reproduced by the
system as metameric matches. Colors outside the color gamut solid volume
cannot be matched. Note: The area of the cross-section from the color
gamut solid is a function of the luminance. Although it is advantageous to
have the widest possible color gamut for the ability to provide metameric
matches for the largest number of colors, the required transformations
from origination colorimetry to colorimetry matched to available display primaries,
for example, may require large matrix coefficients and, therefore, a
signal-to-noise penalty. The choice of color gamut is a compromise
between color rendition and signal-to-noise.
Color Key – See Chroma Key.
Color Killer – Circuitry which disables the receiver’s color decoder if the
video does not contain color information.
Color Lookup Table (CLUT) – The CLUT is a compression scheme where
pixel values in the bitmap represent an index into a color table where the
table colors have more bits-per-pixel than the pixel values. In a system
where each pixel value is eight bits, there are 256 possible values in the
lookup table. This may seem a constraint but, since multiple lookup tables
can be referenced, there can be many tables with varying 256 color
schemes. CLUTs work best for graphics where colors do not have to be
natural.
Color Map – A color map is just a numbered list of colors. Each color is
specified in terms of its red, green, and blue components.
Color Map Animation – In normal animation, the images representing
separate frames are written on separate pieces of artwork. In computer
color map animation, many images can be written into a frame buffer, each
with a different color number. By “cycling” white, for example, through the
color map, so that only one image at a time is visible, the illusion of animation
can be achieved very quickly. PictureMaker’s wireframe test mode
works this way.