Coax (Coaxial Cable) -- A round cable where one of the conductors is a
thin wire running down the middle and the other conductor (usually grounded) is
a cylindrical shell or braid that surrounds the first conductor. Some "two
conductor plus ground" cables have two thin wires running down the middle. Other
cables have one wire in the middle surrounded by two concentric shells. Coax
cable is often used to connect video components. The insulating material that
keeps the center conductor centered determines the quality of the cable and/or
the kinds of video signals that the cable can carry without degradation. Some
people reserve the words "coax cable" to refer to the round 75 Ohm cable that
carries TV signals from an antenna or cable TV system.
Color Difference Video Signal -- Analog Component
Video q.v. So named because the color components consist of the difference
between other commonly seen video signal components, for example red content
minus luminance.
Comb Filter -- An electronic filter whose frequency response when
graphed suggests the teeth of a comb; the filter alternately accepts and rejects
small bands of frequencies "as we progress up the scale". One way of visualizing
what a comb filter does is to draw evenly spaced parallel lines, alternately red
and black, on paper, and then look through a comb held so as to hide all of the
black lines. Such an array of lines could (and does) stand for the luminance and
color content of a video signal and comb filters are used in the more expensive
TV sets to perform the necessary task of separating the two. Notch and bandpass
filters, common on lower priced TV sets as an alternative, produce acceptable
pictures but with more discoloration and limited horizontal resolution.
Component Video -- Not to be confused with
Composite video. A video signal transmitted as at least three separate
components using separate wires or cable. The most common formats are: RGB
(separate signals for red, green, and blue), and analog component
video (Y/Pb/Pr, luminance together with a signal based on blue and a signal
based on red). Using simple circuits, RGB needed to display a picture can be
easily derived from the latter. In order to get RGB using simple circuits, there
must be at least three components supplied. (In algebra, if a problem has three
"unknowns" there must be at least three equations or relationships supplied in
order to solve it.) S-video seemingly has two components, luminance and color,
but the upper and lower sidebands of the (modulated) C signal actually represent
two sub-components. These together with the luminance make up the three
components that simple circuits can in turn convert into RGB.
Composite Video -- Refers to a video signal
where both the luminance component and the color component(s) are transmitted on
a single wire or broadcast in a limited bandwidth. Each of the major systems
NTSC, PAL, and SECAM has its own definition of how the luminance and color are
combined. The luminance and color information must be separated before the
picture can be displayed.
Convergence -- The correct aiming of the three
electron beams in a direct viewed picture tube or three separate pictures
from tubes in a projection TV (for red, blue, and green) to be together at
all times. Without proper convergence, objects on the screen will have colored
halos around them, white lines will seem to have a red, green, or blue line next
to them, and resolution will be poorer. The most common reason for
misconvergence is the coils attached to the neck of the picture tube not in the
proper position which usually takes a time consuming trial and error process to
correct. Often perfect convergence cannot be achieved over the entire screen so
a compromise where the errors are minimized but not completely eliminated must
be accepted. It may be noted that a convergence error of one fifth of one
percent means that one of the electron beams is off by a scan line causing a
halving of the resolution at that spot on the screen. Also "convergence" refers
to the bringing together and integrating of two or more systems or technologies
so that components can be shared. An example is the development and
manufacturing of video monitors suitable for television, movies, entertainment,
and also computers and data display.
Cross Color -- Rainbow swirls amongst or swamping out pinstripes and
other fine detail, caused by small amounts of luminance signal left behind in
the signal going into the color circuits. This situation is the result of
imperfect Y/C separation by the comb filter (or notch and bandpass filters in
less expensive TV sets).
Cross Luminance-- Crawling or hanging dots where color patches meet,
or silk screen effects, caused by small amounts of color signal going into the
luminance circuits. This situation is the result of imperfect Y/C separation by
the comb filter (or notch and bandpass filters in less expensive TV sets)...
CRT (Cathode Ray Tube) -- Electronic vacuum tube in which a thin beam
of electrons is shot through the space inside and against the far wall
(faceplate; screen) or a plate inside.. This includes all picture tubes used in
TV sets or computer monitors.
De-Interlacer -- Device or circuit to convert interlaced video to
progressive scan video with the same number of scan lines per full video frame.
Loosely referred to as a line doubler.
Although "outputting each scan line twice" will produce reasonable progressive
scan video, "de-interlacer" should refer to devices with more sophistication to
interpolate intervening scan lines or fetch scan lines from the previous and/or
next field for a better quality picture.
Digital -- Being expressed or represented as a series of numbers.
Since sound can be graphed on paper as a waveform, it can in turn be described
numerically little by little as the height of each portion of the drawn
waveform from a baseline (X-axis) Sounds and pictures can be recorded, stored,
and played back digitally with no distinguishable difference from the original
if enough numbers are used. In practice, due to the limited storage space (on
tapes and disks) and limited transmission space (bandwidth) compromises have to
be made. For video this shows up as the limitation of a picture to be made up
using an array of independently colored dots, say, 720 across by 480 high (DVD standard here).
Dot Pitch -- The (center to center) spacing between phosphor dots or
stripes of the same color on a TV screen. The smaller the better for picture
sharpness, 0.28 mm is considered the minimum acceptable for a good computer
display, while a typical 20" TV has an 0.81 mm dot pitch and large screen TV's
have dot pitches a bit larger. Unfortunately, small (5 to 9 inch) TV sets have
dot pitches well in excess of the now easily manufactured .28 mm which makes
these products have unnecessarily coarse picture quality. Many TV screens use
vertical stripes rather than dots in which case the dot pitch applies only in
the horizontal direction.
Downconversion -- The reconstruction of a video frame or image to have
a smaller number of scan lines. This must be done to put an HDTV picture on a
standard TV set. See Sampling.
DTV (Digital Television) -- Refers to standard or high definition TV
whose signals are digital during production, transmission, storage, and
reception. Note: Even digital TV signals are converted to analog to pass through
component video or S-video cables and/or just before being displayed on a
picture tube. The fewer analog to digital conversions there are altogether, the
better the overall quality can be.
DVD (originally "Digital Video Disk", now
"Digital Versatile Disk") -- A 5" plastic disk that looks like a compact
disk, using the same concept of microscopic pits arranged in a spiral and read
using a laser. Except for double sided DVD's (CD's come only single sided) the
only way to tell the difference is to look at the label or markings engraved
near the center. Today's DVD's can play a movie with more resolution than 12
inch laser disks and just over four hours in length without the need to stop the
player and turn the disk over. Double sided DVD's can have a "pan and scan" version
of a movie on one side and a wide screen version on the other. Or programs can
be recorded with different camera angles you can choose from. The present NTSC
DVD picture is usually 704 or 720 (occasionally 640) pixels across by 480 pixels
high compared with LD's up to 565 details across (425 lines) and approx. 480
scan lines high. Using S-Video (Y/C) or component video inputs, DVD has much
better color horizontal resolution, up to 270 lines for all colors versus
LD's 40 to 120 lines for different colors. As of May 1998 no consumer products
are available to record one's own DVD's but the promise is there for the future.
A CD player cannot play a DVD; most DVD players can play CD's. For computer use,
the nominal capacity of a DVD is 4.7 gigabytes per layer; there may be one or
two layers per side, and disks may be double sided.
EIA -- Electronic Industries Association, whose members represent
equipment manufacturers and establish standards.
Enhanced for 16:9 -- For DVD, refers to a program
where the entire 720 by 480 pixel video frame represents a 16:9 aspect ratio
image. Whereas for a "standard wide screen" program, only the middle 720 by 360
pixels represent a 16:9 image with the topmost and bottommost pixels unused (see
"letterbox"). To
show the full resolution, the enhanced program must be viewed on a TV or
monitor with an adjustable image height control or a 16:9 aspect ratio screen.
The exact number of pixels of picture height excluding letterbox bars will vary
depending on the exact aspect ratio of the image, although the enhanced version
will still have better resolution than a standard letterbox edition. A DVD
player optionally reconstructs the picture with some loss of vertical resolution
to be viewed on a standard 4:3 TV set without a height control. Enhanced wide
screen programs may also be labeled "anamorphic" or
"high resolution".
Field -- Either just the even lines of an interlaced video image, or
just the odd lines. A field is technically half of the picture.
Footprint -- (1) Roughly speaking, the physical size and shape of the
portion of an object or building, nearest the floor or shelf or ground it is
resting on. For a TV set on legs, the footprint would be the shape described by
a string that encircled all of the legs. For a VCR with rubber feet but no legs,
the footprint would be the shape of the entire body. (2) In an abstract sense,
the irreversible consequences of a format or set of rules. For example, the 720
(or 704 depending on subject matter) pixel wide by 480 pixel high "grid"
representing the DVD picture is a
footprint, which in this context forever constrains the picture data to occupy
discrete pixel positions implied by that grid and not occupy the spaces in
between. Composite
video is also a footprint whose manifestation in a video image is smeared color
boundaries and rainbow effects amidst fine details, among other things. Color
resolution is highly limited and it is almost impossible to get rid of all of
the contamination from each other when the luminance and color information are
finally and mandatorily separated for display of the picture.
4:2:2 -- One method of specifying color
(chrominance) resolution of digital video signals. The first number is the
reference count of luminance pixels. The second number is the corresponding
number of color pixels in the odd rows or scan lines. The third number is the
corresponding number of color pixels in the even rows. DVD's rating is 4:2:0,
the color resolution is half the luminance (advertised; published) resolution
both horizontally and vertically, or each two by two block of luminance pixels
has to be the same color. For analog video luminance and color resolution vary
independently.and the color resolution may vary depending on which colors are
juxtaposed, so this method cannot be easily applied. We could say that
contemporary NTSC broadcasts have a rating of 4:0.5:0.5 (330 lines
luminance, 40 lines color) although unlike digital video the "pixels" on each
scan line don't have to line up vertically or be of uniform size.
Frame -- All of the lines, both odd and even, that make up one
complete "painting" of the video screen. Also any one exposed picture on a strip
of movie film.
Gamma -- The relationship between the brightness of
a spot on the picture tube where the electron beam hit and the level of the
video signal. It can be graphed as a curved line. If twice as many electrons are
fired at the screen, that spot does not look twice as bright to the human eye,
Therefore for video the gamma graph is not straight, or linear. In practicer it
also varies with the make and model of the TV set or monitor, the nature and
quality of the electronics inside, and also the settings of the brightness
and contrast controls. Gamma also applies to film where the intensity of light
hitting the film results in the appropriate intensity of the color in the
finished print or slide. Adjusting gamma is difficult especially considering
that most people cannot tell what is correct unless they have a side by side
comparison with the live subject, a supposedly correct photograph of the
subject, or a TV that is adjusted correctly. Also personal preferences,
comparable to preferences in adjusting stereo bass and treble controls, affects
the settings. Typical test patterns for adjusting the gamma consist of series of
stripes graduated from black to white, some of them using gray scales, others
using halftoning or dithering of pure black and pure white dots. The user is
told to adjust controls on the monitor until some stripes are distinguishable
and others blend into each other. The instructions for using each gamma chart
vary. See, also, Prime Disclaimer
Hard Matte -- Refers to wide screen movies that are filmed using a
camera that blocks off the top and bottom edges of the 4:3 aspect ratio film
frame, recording an image that has the aspect ratio of the finished picture and
leaving unused the top and bottom edges of each frame on the film. (This is how
panoramic 35mm still cameras work.) Some producers use this technique so that
the theater projectionist cannot err (or deliberately modify the presentation)
by opening up the projector's aperture plates too much.
HDTV (High Definition Television) -- A generic term describing TV
signals and equipment providing pictures made up of approximately a million
pixels or more. See also, ATSC.
Horizontal Retrace Interval -- The time during which the electron beam
is turned almost off (as if to draw black) and moved from right to left to
get ready to draw the next scan line on the picture tube. In NTSC broadcast
video, 10.9 microseconds are set aside for this purpose; the entire line,
retrace interval and all, takes 63.5 microseconds.. The time it takes to draw an
entire line is adequate to allow the electron beam to draw at most 530 dots
alternating black and white, given a 4.2 MHz bandwidth; the horizontal retrace
interval takes away about 90 of these dots. Of the remaining 440 (give or take a
few), 330 fit in the largest circle that in turn fits in the 4:3 screen, which
leads to the 330 line horizontal resolution that is often mentioned when it
comes to broadcast TV. The exact number of dots used for the picture material
depends on the program source and the make and model of equipment.
Interlace -- The drawing of all of the odd lines, then all of the even
lines, to display each video frame. Every once in a while a TV set has the
defect (line pairing) of having the even lines not land exactly between the odd
lines, which results in loss of vertical resolution.
I-Frame (Intra-Frame) -- In a video compression scheme, such as
for picture information on a DVD, a frame that is complete. In order to begin
playback, an I-frame must be located. Other frames (B-frames, P-frames, q.v.)
are just the differences from adjacent frames. Thus frame 1 may be an I-frame.
Frame 2 on the DVD might be a P-frame which when combined with frame 1, yields
the complete frame 2 for display. Frame 3 on the DVD might be a B-frame which
when combined with the complete frame 2 we just derived, yields the complete
Frame 3, and so on. Usually there is an I-frame about every ten frames, so the
player doesn't have to hunt too far when resuming playback in the middle of the
program.
I-Q -- Refers to one method of encoding of the color
content of a video signal such that all colors could be depicted using a two
dimensional diagram, more specifically a color wheel. There are two color
signals one (I) of which represents oranges and blues and the other (Q)
represents greens and purples. (Both together are used to represent other
colors.) This choice of colors permits giving the oranges and blues, which the
human eye is more sensitive to, more frequency bandwidth and thus greater color
resolution in NTSC video. The remaining colors had to be limited to about 48
lines of resolution (0.6 MHz sideband width) to keep there from being too much
color information contaminating the medium detailed luminance information in the
composite video signal. Many TV sets today and all consumer VCR's limit color
resolution to a theoretical maximum of 40 lines for all colors due to
inexpensive circuitry. When it is not necessary to construct a composite video
signal, the color signals U and V representing blue and red respectively, are
usually used instead of I and Q. We believe that all of the descriptions on this
page can be understood quite well by persons without tremendously high
intelligence quotients.
Kell Factor -- (As best as we can determine) The
ratio of the number of psychologically perceived analog lines of resolution to
the number of scan lines in interlaced video compared with the perceived
resolution of the same picture reproduced with progressively scanned video. The
larger the better, 0.7 is considered very good. Deficiencies such as scan lines
too thin or too thick, and interlace flickering due to a low scan rate worsen
the Kell factor. Extended Kell Factor -- Our own term for the ratio of
the number of psychologically perceived lines of resolution to the number of
scan lines or pixels (spanning the same distance) taking into account all
possible deficiences including the fact that scan lines or pixels can straddle
details in the original subject leading to in some cases a total blur.
Layer -- A DVD is
constructed of several layers of different materials. There are up to four data
containing layers and the player can play two in sequence without the disk's
being removed and turned over. Each layer can hold approximately two hours of
NTSC video. To play "the other layer" the player's laser beam is refocused
slightly. Layer Change -- The jitter or stutter that sometimes occurs as
the DVD player reaches the end of the recorded material on one layer and
switches to the other layer.
LCD (Liquid Crystal Display) -- A panel on which tiny spots become
transparent or opaque in response to electronic signals and which, given enough
of such spots arranged in a pixel grid, can be used as a video display or in a
video projector.
LD (Laser Disk) -- The accepted abbreviation and
terminology for 12 inch consumer playback only video laser disks (and also 8
inch disks recorded using the same format). The video recording is of a composite
video analog signal with about 5.3 MHz of luminance bandwidth which gives a
maximum horizontal resolution of 425 lines. There are two analog soundtracks and
two digital soundtracks; not all players can play the digital soundtracks. All
players can play both the CAV and CLV disk formats.
Letterbox -- The colloquial term used to
describe a video program where the original scene has a larger (wider) aspect
ratio than the TV screen and is zoomed out (shrunk) so that the entire width
fits in the screen. An inescapable consequence is that there is unused screen
area and wasted scan lines at the top and bottom. The term came about because
viewers had the impression they were looking through a mail slot in a door or
out of the slot of a gigantic mailbox. Not all movies are offered on video this
way because the public continues to demand editions where the entire screen is
filled. Also the vertical resolution of subject matter in letterbox editions is
less compared with full screen pan and scan editions
of movies. Although I have not seen any movies prepared in the following way it
might have been interesting to gauge the public's reaction if instead of black
bars, an image of a theater proscenium curtain appeared above and below the
letterboxed picture.
Line Doubler (...Tripler, ...Quadrupler) -- A set of circuits
whose purpose is to paint each scan line on the picture tube twice (three times,
four times) and thus fill in the gaps between scan lines. A device (with
circuits inside) which converts interlaced video to progressive scan video is
also referred to as a line doubler. It too delivers output that has twice as
many scan lines per second as its input and it may also use the technique
equivalent to painting each scan line twice.
Line Pair -- On a test pattern consisting of closely spaced black
parallel lines on a white background, a line pair is one black line together
with the white space on one side of it. When photographers say lines of
resolution, they mean line pairs.
Lip Sync. Error -- Situation in motion pictures where picture and
sound are not synchronized in time. So named because the error is particularly
noticeable as subject lip movement that does not match the words spoken. For
both film and videotape, the sound head is several inches away from the
projector gate / video heads, and careful adjustment is needed. Video processing
units, such as line doublers that accumulate several frames of video in order to
do their processing, can introduce lip sync. error.
Luminance, or Luma -- Brightness of a
light emitting object, or the portion of a video signal that represents
brightness. Used by itself, the luminance signal is sufficient to produce a full
black and white image. It is said that the luminance signal is responsible for
the picture detail. This is true because as the video standards (NTSC, etc.)
were defined, the luminance signal was given a larger bandwidth to permit the
carrying of all of the picture detail while the color signal was deliberately
constrained to consume less bandwidth and consequently possess less detail.
Those readers who know the difference between "luminance" and "luma" should
refer to Prime
Disclaimer.
Matte -- A means of covering up part of an image. In photography and
video it (as plural) generally refers to the aperture plates or other means of
hiding from view the top and bottom edges, leaving what will ultimately be a
wide screen movie picture. Whereas without the mattes the displayed image would
be taller with extra material at the top and bottom that is really not part of
the presentation.
Monitor -- A person whose duty it is to observe, or equipment that
makes it easier (or possible) for said person to make the desired observations.
A "television monitor" can be simply a TV set without a tuner (channel selector)
or more often these days it is a TV set that has additional video inputs to
accept signals other than through its tuner. The term "monitor" seems to suggest
but really does not stand for better quality. (The full correct term for the
standard TV set with tuner is "television receiver".)
Motion Adaptive -- Refers to de-interlacing line
doublers and comb filters whose processing strategy or formula varies, where
coincidentally the optimum processing depends on whether the subject matter
depicted was stationary/steady or moving/changing. The best devices may vary
their processing dozens of times within a single scan line. The device must
digitize several video fields, save (buffer) them on a rolling basis, and
compare the content in small groups of pixels to determine whether subject
matter was moving or not.
MPA, Maximum Pixels (picture elements, picture
details) Across -- (new) My own term for labeling horizontal resolution
in terms of the entire screen width. This is to establish a distinction from the
traditional lines of resolution measurements across the largest circle that fits
in the screen.
MPAA (Motion Picture Association of America) -- An organization,
primarily of executives of the major movie making houses, which sets policies
and standards for movies, including for their distribution and broadcast.
MPEG (Moving Pictures Experts Group) -- An organization, or more
correctly a large enough collection of groups that could be called an
institution, which among other things developed various data encoding and
compressing schemes so an full length movie could be recorded on a five inch
disk (a DVD).
Native -- Not counting ,or prior to applying, any of: scaling,
upconversion, downconversion, encoding, decodiing, modulation, demodulation,
etc. For example the native resolution of "720p HDTV" is 720 pixels high by 1280
pixels wide but a particular TV set with a native 4:3 aspect ratio resolution of
640 by 480 on an LCD panel can convert a 720p 16:9 program to fit by displaying
half the program's resolution horizontally and vertically, 640 by 360.
NTSC (National Television System Committee) -- U.S.
government and industry committee which defined the 525-line 60 (59.94)
interlaced fields per second analog broadcast TV standard over 50 years ago.
(This format is referred to as NTSC.) Of the 525 scan lines, 480 (give or take a
few) contain the picture and the rest contain synchronizing information, hold
the encoded closed caption text, and provide a time delay to move the electron
beam back to the top of the screen. NTSC is used mainly in North America and
Japan. Originally 30 frames per second, the standard was changed slightly to
29.97 frames per second at the time color was introduced since that change made
it easier to incorporate the color information into what is now a composite
video signal. The change was so small that practically all older TV sets
continued to receive the signal properly without loss of vertical hold.
"Object" (on the screen) -- In the subject matter of a picture, a line
or a patch of color. When quality of reproduced pictures is discussed
technically, it is often necessary to think about small parts as hair, nose,
arm, shirt, shoe, or even "iris of the eye" as opposed to "person". It is like
having to deliberately not see the forest because of the trees.
Overscan -- The adjustment of a TV set so that
all four edges of the video frame are slightly outside the screen. This was done
by TV manufacturers decades ago when TV pictures shrank if the power line
voltage dropped, the latter occurring often when everyone was using a lot of
electricity. With overscan, there would still be enough picture to completely
cover the screen when the picture shrank, and viewers stopped complaining that
TV sets were defective.. However program material at the edges of the screen is
lost. Today's TV sets don't suffer from picture shrinkage as much but overscan
still occurs and too much of it is now regarded as a quality control deficiency.
Still, TV producers keep important material away from the edges of the video
frame, and many video cameras have marked in their viewfinders a "safe area".
Sometimes the electronics in the TV set are deficient (rounded off horizontal
and/or vertical sweep sawtooth waveforms) that the extreme edges of the picture
are "squished" and overscan is deliberately used to hide this distorted material
outside the screen borders.
P-Frame -- In a video compression scheme, the difference between the
complete subject frame and its predecessor. This is the most compact amount of
data needed to generate the subject frame given the complete frame preceding,
but it does not allow backwards single step or playback. See, also, I-Frame.
PAL (Phase Alternate Line) -- A 625 line 50 interlaced
fields per second analog broadcast standard used in many parts of the world but
not the U.S.A. So named because the chroma is phase reversed on every other scan
line to reduce picture artifacts. (NTSC is that way also.) Programs are not
interchangeable with NTSC even though
they may occupy the same broadcast channels or be recorded on videocassettes of
the same size and shape. Programs can be played back on SECAM equipment
where they come out as black and white. There exist VCR's and TV sets that will
play all three formats but they are not common in the U.S.A.
Pan and Scan, or P&S-- Term used to describe a
wide screen movie committed to video with a lesser aspect ratio. The picture is
zoomed in on so that more or all of the TV screen is filled (to satisfy popular
demand and improve vertical resolution), but both sides of the original picture
obviously don't fit. A video technician "pans" the conversion machine (e.g.
telecine) back and forth to capture what he considers or what he was told is the
most important part of each scene while cropping the sides. Even film to film
copies, notably 16mm and 8mm prints, have been made using the pan and scan
technique. When you see the notice "... formatted to fit this screen ..." at the
start of a movie broadcast on TV, that refers to the pan and scan transfer. In
addition to losing "space" as the sides of the picture are cropped, movies as
broadcast often lose "time" as they are "edited for (removal of possibly
objectionable) content and to run in the time allotted".
Pb, Pr -- Refer to the color component video signals B-Y and R-Y
respectively with optimization for analog component video purposes or
transmission.
Picture Height, as in "lines per picture height" -- Reference distance
measurement for resolution of TV screens, used for horizontal as well as
vertical discussion. So chosen because resolution is correctly measured in the
largest circle that fits in the area referred to and for a TV screen the
diameter of such a circle equals "one picture height".
PIP (Picture in a Picture) -- A feature on higher priced TV sets
whereby a small picture for a second program can be displayed in one corner of
the screen. The viewer can switch back and forth as to which program occupies
the whole screen. In order for two broadcasts to be so seen simultaneously the
TV set must have two tuners (channel selectors). More commonly there is only one
tuner and the second program must come from a VCR or other local source.
Pixel, or Pel -- Picture element; the
smallest spot on the screen that can be resolved as having a different
brightness or color from what is next to it. The "number of pixels vertically"
is equal to the number of scan lines; for example if you block off all but a
narrow vertical stripe on the screen, you will see a series of dots, one per
scan line. For a computer screen or digital video, the screen is divided into
several hundred "grid positions" horizontally as well; a pixel must be exactly
one of the grid positions, not half of one and half of the next. For analog TV
pictures, we can say that the number of pixels horizontally is equal to the
maximum number of alternating black and white dots that can be reproduced all
the way across the screen, which equals the aspect ratio times the number
of lines of resolution horizontally.
Prime, as in Y', R', etc. -- The video signal or its
components are correctly referred to by the various terms Y, R-Y, G, Cb,
etc. without the apostrophe or "prime symbol" when the signal has not been
modified to compensate for the gamma of the
picture tube. The prime symbol is added, as in Y', Cb', etc. to refer to a video
signal after gamma compensation. Prime Disclaimer -- To simplify things,
all of the descriptions here ignore the gamma compensation, and the
terms Y, R-Y, etc. are used without the apostrophe throughout.
R-Y -- Video signal component consisting of the picture red content
from which has been subtracted the overall luminance. See B-Y and also see Prime Disclaimer.
Raster -- The illuminated rectangle on the face of a picture tube
produced by the scan lines whether showing a picture, a solid color, or snow.
"Underscan
is when the raster does not fill the screen."
RCA Plug and Jack -- A one conductor plus ground plug and jack
connector introduced by Radio Corporation of America, now part of Thomson
Electronics. The jack is a metal stud a little larger around than a pencil
(about 3/8 inch) with a center hole that a small lollipop stick would fit (about
1/8 inch). The matching plug has one fat (1/8 inch) center pin that represents
the live conductor, and a shell that presses onto the jack stud and that is
almost always grounded. Normally the center pin is connected to the center
conductor of a coaxial cable and the shell is connected to the shell or shield
of the cable.
Receiver -- The best short definition of this term as it applies to
electronics is "a device that captures an over the air broadcast (or satellite
or cable or microwave transmission) and presents it for listening, data
processing, or viewing". A "television receiver" is the complete TV set as we
know it, which includes the cabinet, picture tube, loudspeaker, channel
selector, usually a built in antenna, and all the related electronics. A "radio
receiver" f.k.a. "radiotelephone receiver" is a "radio" as we know it, with
built in antenna, tuning dial, loudspeaker, volume control, etc. But a "stereo
receiver" generally does not include the antenna or loudspeakers, although it
refers to the unit with everything else needed to receive FM stereo broadcasts,
namely the case with built in tuner and tuning dial, amplifiers, volume and tone
controls, sometimes pre-amplifiers for phonographs, etc.
Registration -- Convergence
of the sub-images in each of the primary colors as it applies to the three CRT's
or LCD panels of a projection TV, or plates on printing presses, as opposed to
electron beams that paint one spot at a time on a direct view CRT.
Resolution -- Ability of a system to represent detail, expressed as
pixels, lines or line pairs per some distance such as inches. For visual media,
lines of resolution or line pairs of resolution is traditionally measured across
the largest (perfect) circle that fits in the area being referred to. For a
standard TV screen, such a circle would span 3/4 of the screen width. A
lot of advertising deception involves mis-stating the lines of resolution to
span the entire screen
width. The number of lines of resolution horizontally need not equal the
number of lines of resolution vertically (or diagonally). Because pixels can
straddle and thereby lose detail in a digital system but not in an analog
system, the number of pixels does not equal the number of lines of resolution. In
NTSC analog video, it requires one megahertz of bandwidth counting just to one
side of the carrier to give 80 (79.5) lines of horizontal resolution. If
resolution is expressed in pixels, both the horizontal pixel count and vertical
pixel count spanning the entire screen should be specified.
RF (Radio Frequency) -- For video, refers to the antenna inputs to a
TV set, or the video signal as it is processed by the TV set's tuner. Also
refers to audio channels encoded on video disks by being modulated onto carrier
frequencies as if they were going to be broadcast.
RGB -- A video signal transmitted as three components using three
wires and which are the respective color content of red, green, and blue,
respectively. R, G, B -- The red, green, and blue components referred to
separately. RGBHV -- The RGB signal where horizontal and vertical
synchronization (sub)signals are carried on fourth and fifth wires,
respectively. RGBS -- The RGB signal where horizontal and vertical sync.
are combined (composite sync.) and carried on a fourth wire. RGsB -- The
RGB signal with sync. combined with the green signal so that just three wires
are needed. (There is no such thing as sync. on blue or sync. on red.)
Ringing -- In video, closely spaced repeated ghosts of a vertical or
diagonal edge where dark changes to light or vice versa, going from left to
right. The electron beam upon changing from dark to light or vice versa instead
of changing quickly to the desired intensity and staying there, overshoots and
undershoots a few times. This bouncing could occur anywhere in the electronics
or cabling and is often caused by or accentuated by a too high setting of the
sharpness control.
S-Video (also called Y/C) -- A video signal
transmitted as two components requiring two separate wires: luminance
(technically referred to as Y) and color (C). Although commonly found in S-VHS
VCR's, this signal is not limited to such VCR's. Note: The C portion is already
modulated on a subcarrier, 3.58 MHz (approx) for NTSC as if to be combined with
the Y portion to become composite video, except not already bandwidth limited as
needed to meet specs. Note: S-video can represent interlaced video signals only.
Looking into the S-video cable plug, with the plastic pin in the 6 o'clock
position, upper left (metal) pin is luminance, upper right pin is color, center
metal pins are ground for the respective pins above them. Luminance and color
are recorded separate on all VCR's, using different subcarriers than S-video.
Safe Area -- The portion of the picture area, usually marked so in the
camera's viewfinder, where important material, action, or text titles should be
confined to, and/or extraneous things such as microphone booms kept out of. The
purpose is to make sure that everything important can be seen even when the TV
set has a lot of overscan, or to
create movie and video programs that can be acceptably cropped into a choice of
two or more picture aspect ratios. For video, the safe action area, where
important subject matter is generally confined to, is the inner 81% of the
picture area after discounting edge strips 5% of the respective screen dimension
in width. The safe title area, used for positioning text such as credits,
is the inner 64% of the picture area after discounting edge strips 10% of the
respective screen dimension in width.
Sampling -- The process of converting an analog
entity (such as a picture or a soundtrack) to digital form. In the case of a
picture, a large number of evenly spaced spots (samples) are taken and each
represented as one or more numbers for brightness (luminance) and color. These
spots are referred to as picture elements or pixels. The more samples are taken,
the more accurate (with higher resolution) an image can be reconstructed from
the samples. For DVD, the image is 720 samples wide by 480 samples high for a
total of 345,600 samples (may vary slightly). Even analog TV has sampling; each
scan line is a (digital) sample in the vertical direction although it is
continuous (analog) in the horizontal direction. Resampling -- The
conversion of a set of samples to become a larger or smaller set of samples, for
example a 720 by 480 pixel video frame to a 360 by 240 pixel video frame.
Picture quality is lost irreversibly whenever resampling is done to yield a set
of samples less than twice the original set both horizontally and vertically.
Significant picture quality loss occurs when resampling is done to yield a set
of samples less than about 140% (or reciprocal of the Kell factor) of the
original set in each direction. This is because the only way to figure out what
each new sample should be is to interpolate (guess based on the nearest old
samples).
SAP (Second Audio Program) -- A means of providing a second audio
channel, for such purposes as stereophonic sound or bilingual audio tracks, on a
TV broadcast channel.
Scaling -- Resampling. See Sampling. This
is done to zoom an image on the screen without spreading out the existing scan
lines, or to change the video from one format to another with a different number
of scan lines, for example HDTV to NTSC or NTSC to SECAM.
SDTV (Standard Definition Television) -- Refers generally to digital
or analog TV signals and equipment that provides picture quality roughly the
same as NTSC, that is, having about 500 scan lines.
SECAM (Sequential Couleur Avec Memoire)-- A 625 line
50 interlaced field per second analog broadcast standard used in Europe.
Alternating scan lines carry R-Y and B-Y color difference signals respectively.
The TV must contain delay (memory) circuits to make available both the R-Y and
B-Y signals, which are then shared by (as common to) the two scan lines. Chroma
resolution is half the luminance resolution vertically. Programs are not
interchangeable with NTSC even though
they may occupy the same broadcast channels or be recorded on videocassettes of
the same size and shape. Programs can be played back on PAL equipment where
they come out in black and white. There exist VCR's and TV sets that will play
all three formats but they are not common in the U.S.A.
Selectavision -- Trademark of Thomson Electronics (which acquired
Radio Corporation of America; RCA), refers to certain VCR's and a now obsolete
playback only video disk system that RCA marketed. See CED.
75-Ohm -- Refers to TV antenna connections made using a round
(coaxial) cable. Also refers to the most common video cabling using RCA plugs
and jacks. For RCA video cables, almost any cable will transmit a decent picture
but critical viewers will have to verify whether the circuits are indeed 75 ohm
and purchase cables that match and have adequate bandwidth.
Shadow Mask or Aperture Grill -- A grill with
holes or slots mounted about an inch behind the glass screen of the picture
tube. It physically constrains the electron beam intended for the red phosphor
dots (or stripes) from hitting anything but the red phosphor dots, and so on.
Normally the exact shadow mask that will be installed in a picture tube is used
to assist in printing the phosphor dots on the screen of that picture tube, as
the optical process of printing the phosphor dots closely mimics the path of the
electron beam. Mating a shadow mask with a screen panel early in the
manufacturing process prevents slight variations from one mask to another from
affecting the quality of the finished picture tubes.
Shimmering -- (1) Flickering halos or pinpoints of light caused by
stray light rays from imperfect rear projection screen layers, which
contain lens elements. (2) Accentuated flicker of thin picture details moving up
or down at certain speeds that interact with the scan rate.
Soft Matte -- Refers to wide screen movies that were actually filmed
wide-angle using the entire 4:3 aspect ratio film frame and where the
projectionist adjusts mattes (aperture plates) to hide the top and bottom edges
leaving the middle as a wide screen view. Sometimes what will become a wide
screen film is shot in the 4:3 aspect ratio so that when committed to video, the
entire width of the picture can be included and also the entire TV screen would
be filled. Sometimes the top and bottom edges intended to be matted are not
suitable for inclusion in a video edition because the special effects added
later fell short of these areas or because extraneous things such as microphone
booms were caught in those areas. This writer believes that when a wide screen
movie that was shot soft matte is offered on video with extra material of
interest such as director's notes, scenes from alternate scripts, or behind the
scenes footage, the movie itself should be transferred to video unmatted if not
anamorphic. The material at the top and bottom edges is behind the scenes
material that can be given free of charge on a spherical transfer with no extra
effort by the producer and no loss of picture quality.
Spatially Adjacent -- Refers to scan lines
immediately juxtaposed on the screen. The term is needed when discussing
interlaced video where juxtaposed lines are (for NTSC) 1/60 second apart in
terms of when they were transmitted, received, and "drawn". See, also, Temporally
Adjacent.
Spherical -- Opposite of "anamorphic"; refers to photography or
cinematography where a picture is recorded in its actual horizontal to vertical
proportions. That is, it is not "squished" to fit on a film frame with a lower
(usually 4:3) aspect ratio and where a special lens would be needed to project
it in the correct proportions. In the case of a wide screen movie, the image
occupies the center portion of the film frame and the top and bottom edges of
the frame are hidden by the projector aperture plates if they were not already
covered and left blank by similar plates in the camera during filming.
SVGA (Super VGA) -- An analog computer video signal format with 600
scan lines each normally representing 800 pixels across. We believe that this
format was defined based on a video memory size of half a megabyte for 256
colors, or one 8 bit byte per pixel.
Temporally Adjacent -- Refers to scan lines
transmitted consecutively. The term is needed in discussing interlaced video
where two temporally adjacent lines are both odd or both even. For progressive
scanned video, lines that are temporally adjacent are also spatially
adjacent.
300 Ohm -- Refers to a usually flat TV antenna cable
consisting of two conductors held parallel about 1/2 inch apart by insulating
material.
3-2 Pulldown (or 2-3 pulldown) -- One method of committing a 24 frame
per second movie on film to 60 field per second or 60 frame per second video.
Consecutive film frames are alternately repeated twice and three times on
consecutive video fields or frames. If you single step through a VCR recording
of a movie, you will often see the three-two-three-two pattern.
Tuner -- The part of a radio, TV set, or stereo system that receives
broadcast signals en-masse from an antenna and extracts, via a manually or
remotely operated tuning dial or channel selector, the desired signal or
program.
Twin Lead -- See 300 Ohm above.
TVL (Television Line) -- On a test pattern consisting of closely
spaced parallel lines, a TV line is either one black line or one white space
that separates two adjacent black lines. The term TV Lines was introduced as an
advertising gimmick to make TV, which has significantly less resolution than
photographic film, seem to have more resolution than it does. Photographers,
when they refer to lines of resolution on film, count only the black lines.
Resolution expressed as TV lines (or as EIA) refers to the maximum number of
them that can be side by side and still distinguishable, in the largest circle
that in turn fits in the screen.
TVCR -- A TV set with built in VCR.
UHF (Ultra High Frequency)-- Comment: Channels 70-83 are no longer
used for TV broadcast and TV sets are no longer required to receive them. Other
services such as cellular telephones use this part of the frequency spectrum,
which as a whole extends from about 316 MHz to 3.16 GHz.
Underscan -- Condition when the picture size is
adjusted so that strips of unused screen area are along all borders. Computer
users sometimes leave their monitors adjusted this way to guarantee that
material such as the "start button" in the lower corner of the Windows screen
does not disappear beyond the edge. Also on some TV sets the edges of the
picture suffer distortion when extended all the way to the picture tube edge.
See, also, Overscan.
Unity -- The number 1, when used as a multiplier. Unity Gain
Amplifier -- An amplifier or amplifier stage that doesn't actually amplify,
namely the output is the same as the input. It does have useful purposes, for
example to prevent signals internal to a system from leaking out of an input
jack or port, or to convert from a low voltage high current circuit to a high
voltage low current circuit or vice versa. This writer has seen radios with
several unity gain audio driver stages designed for the sole purpose of having
the radio possess the number of transistors it was advertised to possess.
U-Matic -- A VCR format that uses 3/4 inch wide tape and is somewhat
similar to the now obsolete Beta format.
Upconversion -- The reconstruction of a video frame or image to have a
larger number of scan lines or pixels. See Sampling.
U, V -- The video signal components B-Y and R-Y,
respectively after they are modulated onto a color subcarrier suitable for
subsequent construction of a composite video signal. To produce the picture, the
luminance signal Y is also needed. U and V are used a lot for PAL composite
video. Use of U and V in NTSC composite video is done but it does not quite
optimize the color horizontal resolution to the maximum sensitivity of the human
eye to reddish orange and greenish blue. See, also, I, Q and Prime Disclaimer.
Vertical Filtering -- Video production method used to reduce
flickering of very thin horizontal lines or objects particulary when they are
moving up or down. It consists of blending the content of adjacent scan lines
which of course reduces vertical resolution. It can be done optically, for
example the telecine's
flying spot is a bit larger and captures the average of what it spans on the
film, or electronically, for example scan line 1 as output is the mixture of
lines 1 and 2 from the camera, scan line 2 is the mixture of lines 2 and 3, etc.
Vertical Retrace Interval -- The time during which the electron beam
is moved from the lower right corner to the upper left corner of the screen to
draw the next field. In NTSC video, 1.4 milliseconds, or enough time to draw 21
scan lines, has been set aside for this purpose and to insert information to
synchronize the electron beam with the transmitted picture for maintaining
vertical hold. Typically the electron beam draws 240 odd lines from top to
bottom, then 23 lines while it returns to the top, then draws 240 even lines,
then 22 lines during retrace, and so on. The exact number of lines blacked out
by the TV during retrace and exactly where and how the 525'th line is drawn
varies slightly depending on the program content and the make and model of
the equipment. Once in awhile you see a TV picture criss crossed with several
spurious diagonal lines slanting up from left to right. These are the vertical
retrace scan lines mentioned above but due to a defect they were not made black
enough. For digital video no pixels of data are associated with the vertical
retrace interval but the monitor has to set aside drawing time for it anyway.
Vertical Squeeze Trick -- (A.k.a. 16:9 mode on a
4:3 TV set) Adjusting the vertical size control (height control) downward so all
the scan lines (the raster) occupy a space of the desired aspect ratio (usually
16:9). Used to play 16:9 enhanced DVD's on 4:3 TV sets with with increased
sharpness compared with the 4:3 setting on the DVD player. Whether a particular
TV set can use this technique is a matter of luck since the adjustment may be
complicated or may have side effects such as misconvergence.
VGA (Video Graphic Adapter) -- An analog computer video signal format
or equipment to produce or display same, using 480 visible scan lines each
normally representing 640 pixels. The significance of this format is that the
video signal is made up of the same total number of scan lines (525) transmitted
at the same rate (scan rate) as NTSC video converted to a progressive scan
format. If not confined to a broadcast channel, an (interlaced) NTSC video
signal can also hold the detail of 640 or more pixels across. VGA signals cannot
be sent directly into a standard NTSC video input.
VHF-High, VHF-Low -- There is a frequency gap between the group of VHF
TV channels 2-6 and the group 7-13. The former is referred to as VHF-Low and the
latter as VHF-High. On some TV sets, the tuner controls treat these as two
separate frequency bands and include a switch to select one or the other (and
also the UHF band channels 14-69 as a third switch setting).
VHF vs. VHS vs. VCR -- Don't confuse these three terms.
VCR refers to any video cassette recorder, including 8mm or Beta. VHS stands for
Video Home System, first introduced by the Japanese Victor Co (JVC). VHS
refers to videocassettes with specific physical dimensions, tape
dimensions, and recording format, and the recording equipment that uses such
cassettes. A VHS cassette can contain programs in any of the formats NTSC, PAL,
or SECAM. VHF (very high frequency) refers to a portion of the frequency
spectrum, approx. 32 to 316 megahertz, used for broadcasting and includes TV
channels 2-13.
Many uses of the word "Video" -- (1) "I see" in Latin, (2) Any
electronic signal that represents visual information, or the electronics that
process such signals, (3) A short three minute or so motion picture with a
soundtrack consisting of a single popular song and usually presented on
broadcast television programs or on videotape.
Weave -- Method of de-interlacing where an intervening scan
line is taken from the next field. See also, Bob.
White Flag -- The means whereby a (12") CAV laser disk is encoded so
that the even and odd fields match when the player displays a still frame.
Without white flagging, the laser player may do a still frame with the odd
interlaced field taken from what was one film frame and the even interlaced
field taken from the next film frame. The result is a flickering double exposure
effect. One consequence of correctly white flagged movies originally from 24
frame per second films is that the laser player's frame counter will count 24
frames for one second's worth of playing time. NTSC programs not from film
sources or that are not white flagged will count 30 frames for one second's
worth of playing time. Similar flags are also sometimes encoded on DVD so the
player can reconstruct full frames for output to progressive scan equipment.
Wide Screen -- Refers to a video program whose picture has a wider
aspect ratio than 4:3.
XGA -- An analog computer video format with 768 visible scan lines
each normally representing 1024 pixels across.
Y/C -- Luminance and
Chrominance
(color) video signals, respectively. See, also, S-Video.
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