See also: HDTV Explained
"A
must read before buying an HDTV"
TV
Glossary
16:9
See aspect
ratio, and widescreen.
3-2
pulldown processing
Sophisticated video
processing common to digital TVs and progressive-scan
DVD players. It corrects for artifacts and distortion
that occur when film-based material (at 24 frames per
second) is converted to video (30 frames per second),
then de-interlaced to create a progressive-scan signal.
4:3
See aspect
ratio.
ALiS
ALiS
(Alternate Lighting of Surfaces) is a relatively new
type of high-definition plasma panel design. On a
conventional plasma TV, all pixels are illuminated at
all times. With an ALiS plasma panel, alternate rows of
pixels are illuminated so that half the panel's pixels
are illuminated at any moment (somewhat similar to
interlaced-scanning on a CRT-type TV). ALiS panels offer
bright, clear picture quality, reduced power
consumption, and extended panel life.
Anamorphic
video
Video images that have been "squeezed" to
fit a video frame when stored on DVD. These images must
be expanded (un-squeezed) by the display device. An
increasing number of TVs employ either a screen with
16:9 aspect ratio, or some type of
"enhanced-for-widescreen" viewing mode, so that
anamorphic and other widescreen material can be viewed
in its proper proportions. When anamorphic video is
displayed on a typical TV with 4:3 screen size, the
images will appear unnaturally tall and narrow.
Artifacts
Unwanted visible
effects in the picture created by disturbances in the
video transmission or processing. Examples include "dot
crawl" or "hanging dots" in analog pictures, or
"pixelation" in digital pictures.
Aspect ratio
The ratio
of width to height for an image or screen. The North
American NTSC
television standard uses the squarish 4:3 (1.33:1)
ratio. More and more direct-view and projection TVs
(especially digital TVs) use the wider 16:9 ratio
(1.78:1) to better display widescreen material like
anamorphic DVDs and HDTV broadcasts.
ATSC
Advanced Television
Standards Committee. Formed to establish technical
standards for the U.S. digital television system.
Audio/video
inputs
Using a TV's direct A/V inputs to connect
a DVD player, VCR, camcorder or other video component
provides improved picture and sound quality compared to
using the everything-on-one-wire RF antenna-style input.
(If your TV is old enough that it only has RF-type
inputs, that's reason enough to consider replacing it —
DVD players don't normally have an RF output!)
Rear A/V inputs are used for components you
normally leave connected to your TV. Front A/V inputs
allow you to quickly and easily connect/disconnect a
camcorder, second VCR, or video game console.
Audio outputs
Stereo
audio jacks that let you connect your TV to your stereo
or home theater system. There are two types — fixed, and
variable. If you connect a TV's fixed output to
your A/V receiver, you'll be able to raise and lower the
TV volume via the receiver's volume control. If
you connect the TV's variable output to your
receiver, you would control TV volume using the
TV's remote.
Bitrate
Measured as "bits
per second," and used to express the rate at which data
is transmitted or processed. The higher the bitrate, the
more data that is processed and, typically, the higher
the picture resolution. Digital video formats typically
have bitrates measured in megabits-per-second (Mbps).
(One megabit equals one million bits.) The maximum
bitrate for DVD playback is 10 Mbps; for HDTV it's 19.4
Mbps.
Chrominance
The color
component of a video signal that includes information
about hue (shade) and saturation (intensity).
Comb filter
A comb
filter's task is to remove residual chrominance (color)
information from the luminance (brightness) signal. Comb
filtering enhances fine detail, cleans up image
outlines, and eliminates most extraneous colors. Comb
filters are not required and not used with S-video or
component video connections since those connections
carry the chrominance and luminance information
separately. There are 4 types of comb filters found in
today's TVs:
-
Glass - may also be referred to as an
"analog" comb filter.
-
2-Line Digital - compares consecutive
scanning lines within one field of video and makes
adjustments to reduce cross-color interference.
-
3-Line Digital - compares 3 scanning lines
within a field of video. By comparing more picture
information, a 3-line filter further reduces color
bleeding and dot crawl.
-
3D Digital - not only analyzes consecutive
scanning lines within a field, but also analyzes the
preceding and following fields. Results in improved
color purity and a more stable video image, and nearly
eliminates dot crawl and color bleeding. Also called
3D Y/C.
Component video
The
three-jack component video connection splits the video
signal into three parts (one brightness and two color
signals). Component video has increased bandwidth for
color information, resulting in a more accurate picture
with clearer color reproduction and less bleeding. A
growing number of TVs include component video jacks to
provide the best possible picture quality (better than
S-video
or composite
video) when connected to a compatible DVD player.
Special wide-bandwidth component video
connections are capable of carrying wider bandwidth
video signals, like progressive-scan DVD and digital
television. All HDTV-ready
TVs include at least one set of wide-bandwidth
connections for connecting a separate HDTV tuner (or
progressive-scan DVD player).
Composite video
A
single video signal that contains luminance
(brightness) and chrominance
(color) information. A composite signal is better than
an RF signal, but not as good as S-video
or component
video. A composite video jack is usually a single
RCA-type.
Contrast
ratio
Measures the difference between the
brightest whites and the darkest blacks a display can
show. The higher the contrast ratio, the greater the
ability of a display to show subtle color details and
tolerate ambient room light. Contrast ratio is an
important spec for all types of TV display, but
especially for front
projectors.
CRT
(Cathode-Ray Tube)
A CRT ("picture tube") is a
specialized vacuum tube in which images are created when
an electron beam scans back and forth across the back
side of a phosphor-coated screen. Each time the beam
makes a pass across the screen, it lights up a
horizontal line of phosphor dots on the inside of the
glass tube. By rapidly drawing hundreds of these lines
from the top to the bottom of the screen, images are
created.
The regular "direct-view" TVs that most
people watch have a single large picture tube, while
CRT-based rear-projection and front-projection TVs use
three CRTs: one each for red, green, and blue.
De-interlacing
(also called line-doubling)
The process of
converting an interlaced-scan video signal (where each
frame is split into two sequential fields) to a
progressive-scan signal (where each frame remains
whole). De-interlacers are found in digital TVs and
progressive-scan DVD players. More advanced
de-interlacers include a feature called 3-2
pulldown processing. For TVs, de-interlacing is
often referred to as "line-doubling" or "upconversion."
Digital
audio output
A connection found on HDTVs and HDTV
tuners for sending the Dolby Digital audio of HDTV
broadcasts to an A/V receiver with Dolby Digital
decoding. The two most common types of digital output
are coaxial and Toslink optical.
Direct-view
TV
The conventional and most common type of TV,
which uses a single large (up to 40") CRT
to display images. Other TV types include rear-projection
and front-projection.
DLP (Digital Light
Processing)
A projection TV technology developed
by Texas Instruments, based on their Digital Micromirror
Device (DMD) microchip. Each DMD chip has hundreds of
thousands of tiny swiveling mirrors which are used to
create the image — each mirror represents a single
pixel. DLP technology is used in both front- and
rear-projection systems.
There are two basic
types of DLP projector: "single-chip" projectors use a
single DMD chip along with a spinning color wheel, while
much more expensive "3-chip" projectors dedicate a chip
to each basic color: red, green, and blue.
Dolby® Digital
A
discrete multichannel digital audio format that is the
official audio standard for HDTV (and DVD). Dolby
Digital is normally associated with 5.1-channel surround
sound. Though this channel configuration is common, it
is only one of several possible variations — a "Dolby
Digital" soundtrack can mean anything from 1 to 5.1
channels.
Downconvert
A term used
to describe the format conversion from a higher
resolution input signal number to a lower display
number, such as 1080i input to 480i display. Some HDTV
tuners are able to downconvert digital HDTV signals for
display on a regular analog TV.
DTV (Digital Television)
The new
American digital broadcast TV standard, which began
operation in late 1998, and will eventually replace the
60-year-old analog NTSC
system. DTV comes in two basic flavors: widescreen,
near-film-quality HDTV
(High-Definition Television) with Dolby Digital audio,
and medium-quality SDTV
(Standard-Definition TV).
DVI
(Digital Visual Interface)
A multi-pin
computer-style connection intended to carry
high-resolution video signals from digital set-top boxes
(HDTV-capable DIRECTV, DISHNetwork, and cable boxes,
plus a few DVD players) to HDTV monitors with a
compatible connector. The signals are encrypted with
High-bandwidth Digital Content Protection (HDCP) to
prevent recording.
EDTV
(Enhanced-Definition Television)
A designation
applied to televisions that can not only display signals
in 480-line progressive (480p) mode, but which can also
accept 480p signals from video sources such as
progressive-scan DVD players. 480p picture quality is
superior to standard analog TV (480i), but not as sharp
as true HDTV (1080i or 720p).
Electronic program
guide (EPG)
Provides an on-screen listing of
available channels and program data for an extended time
period (typically 36 hours or more).
Field
In interlaced-scan video,
each complete frame is split into 2 sequential fields,
each of which contains half the scanning lines of the
frame. One field contains the odd scanning lines, and
the other field the even lines.
Flat-panel TV
Any
ultra-thin, relatively lightweight TV — especially those
which can be wall-mounted. Current flat-panel TVs use
either plasma
or LCD
technology.
Frame
A
complete, individual picture in a movie film. In a video
signal, a frame contains all of the picture's scanning
lines. The frame rate of a progressive-scan format is
twice that of an interlaced-scan format.
Frame rate
The rate at
which frames are displayed. The frame rate for movies is
24 frames per second (24 fps). In regular NTSC video,
the frame rate is 30 fps. The frame rate of a
progressive-scan format is twice that of an
interlaced-scan format — example: the frame rate for
480i DVD is 30 fps (or 60 interlaced fields per second);
for progressive-scan DVD at 480p, it's 60 fps.
Front-projection
TV
A 2-piece display system consisting of a
separate front projector (typically placed on a
table or ceiling-mounted) and screen. Front-projection
systems can display images up to 20 feet across, or
larger. Traditionally, CRT
projectors were found only in high-end home theaters,
but compact digital projectors using DLP
or LCD
technology have lowered the cost of front-projection
systems considerably.
Gain
Measures the
light-reflecting ability of a projection screen. The
higher the number, the greater the amount of light
reflected back to the viewer(s).
HDCP (High-Bandwidth Digital Content
Protection)
HDCP encryption is used with
high-resolution signals over DVI
and HDMI
connections and on D-Theater D-VHS recordings to prevent
unauthorized duplication of copyrighted material.
HDMI (High-Definition
Multimedia Interface)
Similar to DVI (but using
much smaller connectors), the multi-pin HDMI interface
transfers uncompressed digital video with HDCP copy
protection and multichannel audio. Using an
adapter, HDMI is backward-compatible with most current
DVI connections.
HDTV
(High-Definition Television)
Often mistakenly
used as a generic description of all digital television,
HDTV specifically refers to the highest-resolution
formats of the 18 total DTV formats. Although there
still isn't 100% agreement among manufacturers,
retailers, journalists, etc., true HDTV is generally
considered to be 1,080-line interlaced (1080i) or
720-line progressive (720p).
HDTV-ready
Term used to
describe TVs which can display digital
high-definition TV formats when connected to a
separate HDTV tuner. These TVs generally have
built-in tuners for receiving regular NTSC broadcasts,
but not digital. An HDTV-ready TV may also be referred
to as an "HDTV monitor."
IEEE 1394 (also FireWire or
i.LINK)
First conceived by Apple Computer (as
FireWire®), then developed by the IEEE (Institute of
Electrical and Electronics Engineers), this high-speed
2-way connection allows easy transfer of digital data
between consumer electronics gear and computers. Found
on some HDTV-capable TVs, tuners, and recorders.
Interlaced
scan
In a television display, interlaced scan
refers to the process of re-assembling a picture from a
series of video signals. The "standard" NTSC system uses
525 scanning lines to create a picture (frame). The
frame/picture is made up of two fields: The first field
has 262.5 odd lines (1,3,5...) and the second field has
262.5 even lines (2,4,6...). The odd lines are scanned
(drawn on the screen) in 1/60th of a second, and the
even lines follow in the next 1/60th of a second. This
presents an entire frame/picture of 525 lines in 1/30th
of a second.
Analog NTSC video uses interlaced
scanning, as do several digital television formats.
Formats that include an "i" (1080i, 480i) use interlaced
scanning. See also progressive
scan.
Keystone
correction
"Keystoning" is a form of video image
distortion that occurs with front projectors if the
centerline of the projector's lens is not perpendicular
to the screen. Keystoning results in an image which is
shaped like a trapezoid rather than a rectangle — the
top of the picture is wider than the bottom, or the left
side is taller than the right, or vice versa. Most front
projectors include "keystone correction" to correct this
distortion. Some models have vertical keystone
correction, while others include both vertical and
horizontal correction. Although keystone correction
allows greater mounting flexibility, it is a form of
processing which usually has a slight softening and
dimming effect on the picture.
LCD (Liquid Crystal
Display)
Liquid Crystal Display technology is one
of the methods used to create flat-panel TVs. Light
isn't created by the liquid crystals; a light source
(bulb) behind the panel shines light through the
display. The display consists of two polarizing
transparent panels and a liquid crystal solution
sandwiched in between. An electric current passed
through the liquid causes the crystals to align so that
light cannot pass through them. Each crystal acts like a
shutter, either allowing light to pass through or
blocking the light. The pattern of transparent and dark
crystals forms the image.
LCD technology is used
in direct-view, rear-projection,
and front-projection
TVs, and is fundamentally different from the CRT
technology used in conventional TVs.
LCoS (Liquid Crystal on
Silicon)
A projection TV display technology that
sandwiches a layer of liquid crystal between a cover
glass and a highly reflective, mirror-like surface
patterned with pixels that sits on top of a silicon
chip. These layers form a microdisplay that can be used
in rear-projection
and front-projection
TVs.
Letterboxed video
A
method for displaying the entire picture as seen in a
movie theater. The resulting image width is much greater
than its height. On a TV screen with standard aspect
ratio (4:3), letterboxed videos appear with horizontal
black bars above and below the image.
Light output
Measures
the amount of light produced by a front
projector. Expressed in "lumens" or "ANSI lumens,"
with a higher number indicating greater light output.
Lumen
The unit of
measure for light
output of a projector. Different manufacturers may
rate their projectors' light output differently. "Peak
lumens" is measured by illuminating an area of about 10%
of the screen size in the center of the display. This
measurement ignores the reduction in brightness at the
sides and corners of the screen.
The more
conservative "ANSI lumens" (American National Standards
Institute) specification is made by dividing the screen
into 9 blocks, taking a reading in the center of each,
and averaging the readings. This number is usually
20-25% lower than the peak lumen measurement.
Luminance
The brightness or
black-and-white component of a color video signal.
Determines the level of picture detail.
MHz (Megahertz)
Equal to one
million Hz. Video signal bandwidth is typically
expressed in megahertz.
MPEG-2
The video compression
standard used for digital television, DVD, and
small-dish satellite TV. This adaptive, variable bitrate
process is able to allocate more bits for complex scenes
involving a lot of motion, while reducing the bits in
static scenes. MPEG stands for Moving Picture Experts
Group.
MTS (Multichannel
Television Sound)
The method of broadcasting
stereo sound over ordinary analog TV channels. MTS
reception capability is built into virtually all stereo
TVs and HiFi VCRs.
NTSC
Stands for National
Television System Committee, which established our North
American 525-line analog broadcast TV standard about 60
years ago. Although it is referred to as a "525-line"
standard, we're only able to see 480 lines on a TV
display. The new DTV
digital broadcast standard will eventually replace NTSC.
Pan-and-scan
The process
of transferring a movie or other source material to
videocassette, DVD, or broadcast so that it fits the 4:3
aspect ratio of the NTSC system, as well as most current
TVs. This results in a significant amount of lost
picture information, particularly in the width of the
image.
At the beginning of a movie on
videocassette, you'll usually see a disclaimer about the
movie having been "...formatted to fit your TV." That
means it's been converted to pan-and-scan.
Picture-in-picture (PIP)
There
are two basic types: 1-tuner picture-in-picture models
require that you connect a VCR or other video component
to provide the source for your second picture. 2-tuner
picture-in-picture models have two built-in TV tuners,
so you can watch two shows at once using only the TV.
Pixel
Short for
"picture element." The smallest bit of data in a video
image. The smaller the size of the pixels in an image,
the greater the resolution.
Plasma
Gas-plasma technology
is one of the methods used to create flat-panel TVs.
Besides enabling thin, lightweight TVs that can be hung
on the wall, plasma offers other advantages. The display
consists of two transparent glass panels with a thin
layer of pixels sandwiched in between (think of this
layer as containing around one million tiny fluorescent
bulbs — the pixels). Each pixel is composed of three
gas-filled cells or sub-pixels (one each for red, green
and blue). A grid of tiny electrodes applies an electric
current to the individual cells, causing the gas to
ionize. This ionized gas (plasma) emits high-frequency
UV rays which stimulate the cells' phosphors, causing
them to glow, which creates the TV image.
Progressive
scan
Some digital television broadcast formats
(720p, 480p), and some higher-end DVD players, use a
type of video signal known as progressive scan. Instead
of splitting each video frame into two sequential fields
like standard interlaced
NTSC video, progressive-scan video displays the entire
frame in a single sweep. So, where standard NTSC video
displays 30 frames (60 fields) per second, progressive
scan displays 60 full frames per second.
Displaying progressive-scan video requires more
bandwidth (there's twice as much vertical information)
and a faster horizontal scan frequency than interlaced
video. Progressive-scan picture quality is more
filmlike, with more fine detail and less flicker. For
progressive-scan viewing, you'll need a TV that's HDTV-ready.
QAM (Quadrature Amplitude
Modulation)
A digital modulation format used for
downstream transmission in cable TV systems — commonly
used for cable HDTV.
Rear-projection
TV
Typically referred to as "big-screen" TVs,
these large-cabinet TVs generally have screens measuring
at least 40". Until recently, all rear-projection TVs
used three CRTs,
which projected images against a mirror inside the
cabinet, so that the images were then reflected onto the
built-in screen. Newer rear-projection technologies
include LCD,
and DLP.
Resolution
The
sharpness of a video image, signal or display, generally
described either in terms of "lines of resolution," or
pixels.
The resolution you see depends on two factors: the
resolution of your display and the resolution of the
video signal. Since video images are always
rectangle-shaped, there is both horizontal
resolution and vertical resolution to
consider.
-
Vertical resolution: The number of
horizontal lines (or pixels) that can be resolved from
the top of an image to the bottom. (Think of hundreds
of horizontal lines or dots stacked on top of one
another.) The vertical resolution of the analog NTSC
TV standard is 525 lines. But, some lines are used to
carry other data like closed-captioning text, test
signals, etc., so we end up with about 480 lines in
the final image, regardless of the source. So,
all of the typical NTSC sources — VHS VCRs, cable and
over-the-air broadcast TV (analog), non-HD digital
satellite TV, DVD players, camcorders, etc. — have
vertical resolution of 480 lines. DTV
(Digital Television) signals have vertical resolution
that ranges from 480 lines for SDTV, to 720 or 1080
lines for true HDTV.
-
Horizontal resolution: The number of
vertical lines (or pixels) that can be resolved from
one side of an image to the other. Horizontal
resolution is a trickier concept, because while the
vertical resolution of all analog (NTSC) video sources
is the same (480 lines), the horizontal resolution
varies according to the source. Some examples for
typical sources: VHS VCRs (240 lines), analog TV
broadcasts (330 lines), non-HDTV digital satellite TV
(up to 380 lines), and DVD players (540 lines). DTV
signals have horizontal resolution that ranges from
640 lines for SDTV, to 1280 lines (for 720p HDTV) or
1920 lines (for 1080i HDTV).
RF (radio frequency)
jack
Sometimes referred to as a "75-ohm coaxial"
connection, this kind of jack is commonly used for
bringing signals from antennas and other sources outside
the home to components with some type of tuner, such as
cable boxes, HDTV tuners, VCRs, satellite receivers,
TVs, etc. A 75-ohm coaxial cable can carry video and
stereo audio information simultaneously. However, as a
way of making a video connection between components, RF
is inferior to composite,
S-video,
and component
video. RF cable connectors (often called "F-type"
connectors) either screw onto the 75-ohm jack, or just
push on to connect.
There are different types of
coaxial cable. Standard coaxial cable is stamped
"RG-59"; higher-quality "RG-6" cable features better
shielding, and exhibits less high-frequency loss over
longer runs. (For connecting DBS satellite systems, it's
essential to use RG-6 cable to correctly pass the
entirety of the digital signal.)
Scaler
Circuitry that converts
a video signal to a resolution other than its original
format. Scaling can involve upconversion or
downconversion, and may also include a conversion
between progressive- and interlaced-scan formats. A
scaler can be built into a TV, HDTV tuner, or DVD
player, or may be a standalone component.
SDTV (Standard-Definition
Television)
A digital television system that is
similar to current standards in picture resolution and
aspect ratio. The picture and sound will be clearer than
NTSC, and its digital base will allow more than one
program to be broadcast over the same bandwidth at the
same time. Typical SDTV resolution is 480i or 480p.
Set-top box
(STB)
Also called converter boxes, these
receivers convert broadcasts (either analog cable,
digital cable, or HDTV) for display on a television.
HDTV-ready TVs (those without a built-in HDTV tuner)
must be connected to a compatible HDTV tuner set-top box
in order to receive digital television programs.
S-video
Found on
nearly all of the TVs we sell, this 4-pin connector
usually provides a sharper, higher resolution picture by
transmitting the chrominance and luminance portions of a
video signal separately. The signals can then be
processed separately, reducing interference. Direct
S-video connections generally outperform composite
connections when hooking up high-performance video
components like DVD players, DBS receivers, and S-VHS
and Hi8 recorders and camcorders.
Upconversion
The term
used to describe the conversion of a lower apparent
resolution to a higher one. This process increases the
number of pixels and/or frame rate and/or scanning
format used to represent an image by interpolating
existing pixels to create new ones at closer spacing. As
an example, Sony TVs with Digital Reality Creation™ can
upconvert 480i video sources to 960i. Often referred to
as "line-doubling."
Widescreen
When used to
describe a TV, widescreen generally refers to an aspect
ratio of 16:9, which is the optimum ratio for
viewing anamorphic
DVDs and HDTV
broadcasts.
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