3:2 Pull-Down: Movie video is recorded at 24 frames per second. NTSC
video is presented at 30 frames per second. 3:2 Pull-Down is the
technical term used to transfer movie video to NTSC video by manipulating
the frames to ensure the movie is displayed correctly at the NTSC video
frame rate of 30 frames per second.
Top
A
Aspect Ratio: Aspect ratio is the ratio of
the width of an image to its height. For example, a projector with a 16:9
aspect ratio will produce an image that is 16 units wide for every 9 units
high. This is also referred to as 1.78:1 meaning the width is 1.78 times
the height. For example, if you want an image 40 inches high then you need
a screen that is at least 40 * 1.78 inches wide or 71 inches. Other common
aspect ratios are 3:2, 4:3 and 5:4.
Native aspect ratio refers to
the aspect ratio of the physical displays built into the projector. For
example, a 1280 x 720 pixel display has a 16:9 native aspect ratio. A
display that is 640 x 360 pixels is also a 16:9 aspect ratio, but with a
fourth of the resolution of the other display.
Nearly every
projector today will support multiple aspect ratios; however each
manufacturer must decide who their intended audience is and optimize the
projector for that audience. This means each projector has a native aspect
ratio that is optimized for specific viewing material. Images shown in
native aspect ratio will utilize the entire resolution of the display and
achieve maximum brightness. Images shown in other than native aspect ratio
will always have less resolution and less brightness than images shown in
native aspect ratio.
Top
B
Brightness:
This is measured in Lumens and is
used to describe how much light is emitted. A higher
lumens value equates to more light.
Top
C
Component Video: Component Video is a
method of delivering quality video (RGB) in a format that contains all the
components of the original image. These components are referred to as luma
and chroma and are defined as Y'Pb'Pr' for analog component and Y'Cb'Cr'
for digital component. Component video is available on some DVD players
and projectors.
Top
Composite Video Signal: The
combined picture signal, including vertical and horizontal blanking and
synchronizing signals.
Top
Contrast Ratio: The ratio between white
and black. The larger the contrast ratio the greater the ability of a
projector to show subtle color details and tolerate extraneous room light.
There are two methods used by the projection industry: 1) Full
On/Off contrast measures the ratio of the light output of an all
white image (full on) and the light output of an all black (full off)
image. 2) ANSI contrast is measured with a pattern of 16
alternating black and white rectangles. The average light output from the
white rectangles is divided by the average light output of the black
rectangles to determine the ANSI contrast ratio. When comparing
the contrast ratio of projectors make sure you are comparing the same type
of contrast. Full On/Off contrast will always be a larger number
than ANSI contrast for the same projector.
Top
D
dB: Often spelled out as decibels, for projector
systems this value measurement is frequently used to describe the amount
of noice the presentation device creates. A higher decibel level
equates to a louder fan. Decibels are measured on a logarithimic scale.
This means that the difference between 40 dB and 39 dB is significantly greater
than the difference between 39 dB and 38dB.
Top
DCDi: Directional Correlation Deinterlacing (DCDi)
was developed by Faroudja and is a video algorithm designed to
eliminate jagged edges that are generated by interlaced video.
Top
Diagonal Screen: The diagonal of a
screen can be computed by squaring the width, squaring the height, adding
them together and taking the square root.
Top
DLP: DLP stands for
Digital Light Processing. The commercial name for this technology from Texas Instruments
(TI): The technology inside is often referred to as either
"micro-mirrors", or DMD: It works this way: build a few hundred thousand
tiny mirrors, and line them up in 800 rows of 600 mirrors each. Now attach
a hinge to each of those 480,000 mirrors. Attach each of those 480,000
hinges to its own very tiny motor! Power each motor with electrostatic
energy! The motors tilt their mirrors up to 20 degrees at incredible
speeds. This allows the mirrors to modulate light from a lamp, and send
the "modulated signal" out through a lens, on to a screen. The most
amazing part of DLP micro mirrors, is the scale of size. The 480,000
mirrors (actually 580,000 are used), hinges and motors are packed onto a
"wafer" a bit larger than your thumbnail.
Top
DTV: DTV refers to the three types of
digital television including Standard Definition Television (SDTV),
Enhanced Definition TV (EDTV), High Definition Television (HDTV).
Top
DVI: DVI stands for Digital Visual Interface. DVI is a
standard that defines the digital interface between digital devices such
as projectors and personal computers. For devices that support DVI, a
digital to digital connection can be made that eliminates the conversion
to analog and thereby delivers an unblemished image. Click
for more details on DVI. Specifications on DVI are available at www.ddwg.org.
Top
E
EDTV: EDTV stands for extended definition
television and is a class of digital television (DTV) that refers to the
480p format. 480p is a progressive scan video format that produces a full
frame of 480 lines of video.
Top
F
Focal Length: The distance from the surface
of a lens to its focal point.
Top
H
HDCP: HDCP (High-bandwidth Digital Content
Protection) is a method for protecting copyrighted digital content that
uses the DVI (Digital Visual Interface) or HDMI (High-Definition
Multimedia Interface, previously known as DVI-CE) by encrypting its
transmission between the video source such as a set-top box, DVD player,
or computer and the digital display device such as a projector, monitor or
television. To view digital HDCP protected content, both the sending and
receiving device must support HDCP.
Top
HDMI: HDMI (High Definition Multimedia Interface)
is an uncompressed, all-digital audio/video interface that supports
audio/video sources such as a set-top box, DVD player, A/V receiver, and
video monitors such as a digital projector or digital television (DTV).
HDMI is backward compatiable with DVI 1.0 specification and supports
HDCP.
HDMI supports standard, enhanced, or high-definition video,
plus multi-channel digital audio, and interactive controls on a single
cable. It transmits all ATSC (Advanced Television Systems Committe) HDTV
standards and supports 8-channel digital audio. First product releases
using HDMI occurred in 2003.
Top
High Gain Screen: A screen that uses
one of many methods to collect light and reflect it back to the audience,
which dramatically increase the brightness of the image over a white wall
or semi-matte screen. Technologies used include curved screens, special me
tal foil screens (some polarized), and certain glass bead screens. Prices
and performance vary tremendously.
Top
I
Instant Rebate: A discount provided to
the purchaser during the checkout process. This discount will be
displayed as part of the total, immediately before the purchaser enters
any credit card information.
Top
Interlaced Video: Video systems in
which each frame of video consists of two video fields. The odd numbered
lines are contained in the first field and the even numbered lines are
contained in the second field. When the image is delivered to a video
device such as a television, the odd and even fields are delivered at 50
or 60 fields per second and your eye sees an integrated image.
Top
Invert Image: Invert image flips the image
from top to bottom, to compensate for ceiling mounting a projector upside
down. Projectors typically ceiling-mount upside down, because most have
"keystone" correction built in to compensate for the distortion created by
"pointing up" from the table to the screen. Usual positioning has the
projector about even with the bottom of the screen in a "table top
position," or, even with the top of the screen when ceiling
mounted.
Top
K
Keystone: Keystoning occurs when the projector
is not perpendicular to the screen, thereby creating an image that is not
rectangular.
Top
Keystone Correction: Keystone
correction makes a projected image rectangular. This can be accomplished
by positioning the projector to be perpendicular to the screen. Since this
is not always possible, most projectors are equipped with keystone
correction that allows the image to be keystone corrected (made
rectangular) by adjusting optics, making mechanical adjustments, or
applying digital correction to the image. Keystone correction can be one
or two dimensional and manual or automatic depending on the projector and
the manufacturer.
Top
L
LCD:
LCD stands for liquid crystal display. Its primary purpose is to present a
digital image for viewing. A common use of LCDs is as a display on a
notebook computer.
Top
Lens Shift: The Lens Shift feature of a
projector allows the optical lens to be physically shifted up and down
(Vertical) or left and right (Horizontal). Most all lens shift mechanisms
are motorized with vertical lens shift being the most popular. With a
projector that has lens shift you can optically correct for keystone
distorted images. It is also used to help geometrically align images when
stacking projectors.
Top
Letterbox: A method of preserving the
originally aspect ratio of a production when presented on a projector with
a different aspect ratio. This is accomplished by showing the full image
and black where no image exists.
Top
Long Throw Lens: A lens designed for
projection from the back of a room, or rather the back of a long room.
Long throw lenses would be used a projection booth in the back of a
theater, etc. A typical long throw lens might have to be 50 to 100 FT back
to project a 10FT diagonal image.
Top
Lumens: A standard for measuring light
output, used for comparing projectors. Unfortunately, there are enough
variables, that the eye will often disagree radically with the ANSI
rating. At best, ANSI lumens do fairly well comparing "apples" to
"apples". If however one projector uses Halogen lamps and another
metal-halide, the halogen projector will seem noticeably dimmer even if
the two units rate the same. Other variables, including type of LCD
technology (active matrix TFT, Poly-Si, passive), type of overall
technology (LCD vs.DLP vs. CRT), contrast ratios, etc. all effect the end
result.
Top
M
Maximum Distance: Sometimes, rarely,
the distance from the screen that a projector can focus the image. Most of
the time, it is the manufacturer's opinion of how far from a screen the
projector can be to cast an image that is useable (bright enough) in a
fully darkened room. Generally this is very subjective. One projector
might quote a distance that allows them to produce a 25FT diagonal image,
while another, brighter projector might quote a distance that only equates
to a 20FT image. Beware!
Top
Maximum Image Size: The largest image
a projector can throw in a darkened room. This is usually limited by focal
range of the optics.
Top
Maximum Resolution: Maximum
Resolution refers to the highest resolution that a given projector can
display. If the Maximum Resolution exceeds the Native Resolution, the image is usually
scaled to match or approximate the Native Resolution of the
projector. Scaling reduces the image resolution and produces some
artifacts in the image that are more apparent when viewing text than
graphics or video.
Top
Minimum Distance: The closest position
that a projector can focus an image onto a screen.
Top
N
Native Resolution: Native
Resolution refers to the number of physical pixels in a display
device. For example, an SVGA projector has 800 physical pixels of
resolution horizontally and 600 pixels vertically or 480,000 total pixels.
This is the native resolution of the projector. Projectors are capable of
projecting greater or smaller resolution images into the same physical
resolution through scaling. Scaling reduces the resolution of larger
images and increases the resolution of smaller images to match the native
resolution of the display device. This type of digital scaling always
produces some artifacts in the image that are more apparent when viewing
text than graphics or video. Maximum
Resolution, as mentioned in the projector specs at
ProjectorCentral, refers to the largest resolution that the projector can
scale to fit the Native Resolution.
Top
NTSC: The United States standard for video and
broadcasting and is also used in the western hemisphere, Japan, and other
Asian countries. NTSC standards are 525 lines of resolution transmitted
within a 6MHz channel at 30fps.
Top
O
OHP: The common abbreviation for overhead
projector.
Top
Overhead Projector (OHP): A
device consisting of a light source, a transmissive or reflective
platform, and a focusable lens assembly. An OHP is designed to project
images from tranparencies onto a screen. LCD projection panels are
designed to be used with transmissive OHPs and work best with OHPs that
produce at least 3,000 lumens. Since 5% to 10% of the light that shines
through an LCD panel gets onto the screen, a 3000 lumen OHP will produce
an image of 150 to 300 lumens. Transmissive OHPs are fairly bulky (bigger
than many projectors). Reflective OHPs are fairly portable but are not
useful with LCD projection panels.
Top
P
PAL: A European and international broadcast standard
for video and broadcasting. Higher resolution than NTSC.
Top
Power Zoom : A zoom lens with the zoom in
and out controlled by a motor, usually adjusted from the projector's
control panel and also the remote control.
Top
Progressive Scan: A type of display in
which all the horizontal lines of an image are displayed at one time in a
single frame, unlike an interlaced scan in which a frame consists of two
separate fields with the first field consisting of odd horizontal lines
and the second field even horizontal lines. Progressive scan is used by
projectors, computer monitors, some TVs and HDTV systems, and some digital
camcorders.
Top
Projector: A projector is a device that
integrates a light source, optics system, electronics and display(s) for
the purpose of projecting an image from a computer or video device onto a
wall or screen for large image viewing. There are hundereds of products
available in the market and they are differentiated by their resolution,
performance and features. These devices attached to a computer or video
device as you would connect a monitor.
Top
Q
QXGA:
A QXGA
display has 2048 horizontal pixels and 1536 vertical pixels giving a total
display resolution of 3,145,728 individual pixels that are used to compose
the image delivered by a projector. A QXGA display has 4 times the
resolution of an XGA display.
Top
R
Rear Screen Projection: Using an
opaque screen, the projector is placed behind the screen, invisible to the
audience. It projects onto the screen and the audience sees it on the
other side. Good rear projection screens actually produce brighter images
than some standard screens. So as not to waste space behind the screen,
ideally a projector with a short throw lens is used. Since the projector
can be placed even with the middle of the screen, without blocking
anyone's view, keystoning is not a problem. Some mid-room projectors like
the Epson have available 3rd party short throw lenses. Since the image is
projected through the screen, the image must be reversed.
Top
Reverse Image: Reverse image is a feature
found on most projectors which flips the image horizontally. When used in
a normal forward projection environment text, graphics, etc, are
backwards. Reverse image is used for rear projection.
Top
RGB: Red, Green, Blue; the normal type of monitor
used with computers, examples of usage: RGB input or output often referred
to as Computer input or output.
Top
S
S-Video: A video transmission standard that uses
a 4 pin mini-DIN connector to send video information on two signal wires
called luminance(brightness, Y) and chrominance(color, C). S-Video is also
refered to as Y/C. A composite signal, typically found coming out of an
RCA jack on the back of most VCRs has the Y and C information combined
into one signal. The advantage of having luminance and chrominance
separated is that a comb filter is not needed inside the video projector
to separate the composite signal into the luminance and chrominance
signals. A comb-filter can reduce the sharpness of your video image.
Top
SDTV: SDTV stands for standard definition
television and is a class of digital television (DTV) that refers to the
480i format. 480i is an interlaced video format that produces a full frame
of 480 lines of video in two successive fields. The first field includes
the odd lines and the second field includes the even lines.
Top
SECAM: A French and international broadcast
standard for video and broadcasting. Higher resolution than NTSC.
Top
Short Throw Lens: A lens designed to
project the largest possible image from short distance. Most front room
projectors use short throw lens. They are often required for rear
projection, where the depth behind the screen is limited. A typical short
throw lens might produce a diagonal image size of 10 FT, from a distance
of 7 to 10 FT.
Top
SVGA: SVGA is used to define a specific display
resolution. Resolution is defined by the number of individual dots that a
display uses to create an image. These dots are called pixels. An SVGA
display has 800 horizontal pixels and 600 vertical pixels giving a total
display resolution of 480,000 individual pixels that are used to compose
the image delivered by a projector.
Top
SXGA: SXGA is used to define a specific display
resolution. Resolution is defined by the number of individual dots that a
display uses to create an image. These dots are called pixels. An SXGA
display has 1280 horizontal pixels and 1024 vertical pixels giving a total
display resolution of 1,310,720 individual pixels that are used to compose
the image delivered by a projector.
Top
T
U
UXGA: UXGA is used to define a specific display
resolution. Resolution is defined by the number of individual dots that a
display uses to create an image. These dots are called pixels. A UXGA
display has 1600 horizontal pixels and 1200 vertical pixels giving a total
display resolution of 1,920,000 individual pixels that are used to compose
the image delivered by a projector
Top
V
VGA: VGA is used to define a specific display
resolution. Resolution is defined by the number of individual dots that a
display uses to create an image. These dots are called pixels. A VGA
display has 640 horizontal pixels and 480 vertical pixels giving a total
display resolution of 307,200 individual pixels that are used to compose
the image delivered by a projector.
Top
VGA Cable:
This
cable is typically used to connect a PC to a display device including
monitors, flat panels and projectors. The connectors usually contain 15 pins however
not all of these pins are actually used to transmit a
signal. The signal is always analog.
Top
W
Wi-Fi: Wi-Fi is Wireless Fidelity and is based on
the IEEE 802.11 specifications for wireless local area networks (WLAN)
developed by a working group of the Institute of Electrical and
Electronics Engineers (IEEE). There are four specifications in the family:
802.11, 802.11a, 802.11b, and 802.11g. All four use the Ethernet protocol
and CSMA/CA (carrier sense multiple access with collision avoidance) for
path sharing.
Top
Wi-Fi (802.11a): An IEEE specification
for wireless networking that operates in the 5 GHz frequency range (5.725
GHz to 5.850 GHz) with a maximum 54 Mbps data transfer rate. The 5 GHz
frequency band is not as crowded as the 2.4 GHz frequency, because the
802.11a specification offers more radio channels than the 802.11b. These
additional channels can help avoid radio and microwave interference.
Top
Wi-Fi (802.11b): International standard
for wireless networking that operates in the 2.4 GHz frequency range (2.4
GHz to 2.4835 GHz) and provides a throughput of up to 11 Mbps. This is a
very commonly used frequency. Microwave ovens, cordless phones, medical
and scientific equipment, as well as Bluetooth devices, all work within
the 2.4 GHz frequency band.
Top
WSXGA: WSXGA defines a class of SXGA displays with
a width resolution sufficient to create an aspect ratio of 16:9.
Resolution is defined by the number of individual dots that a display uses
to create an image. These dots are called pixels. A WSXGA display has 1920
to 1600 horizontal pixels and 1080 to 900 vertical pixels respectively
that are used to compose the image delivered by the projector.
Top
WXGA: WXGA defines a class of XGA displays with a
width resolution sufficient to create an aspect ratio of 16:9. Resolution
is defined by the number of individual dots that a display uses to create
an image. These dots are called pixels. A WXGA display has 1366 to 1280
horizontal pixels and 768 to 720 vertical pixels respectively that are
used to compose the image delivered by the projector.
Top
X
XGA: XGA is used to define a specific display
resolution. Resolution is defined by the number of individual dots that a
display uses to create an image. These dots are called pixels. An XGA
display has 1020 horizontal pixels and 768 vertical pixels giving a total
display resolution of 783,360 individual pixels that are used to compose
the image delivered by a projector.
Top
Z
Zoom Lens: A lens with a variable focal length
providing the ability to adjust the size of the image on a screen by
adjusting the zoom lens, instead of having to move the projector closer or
further.
Top
Zoom Lens Ratio: Is the ratio between
the smallest and largest image a lens can projector from a fixed distance.
For example, a 1.4:1 zoom lens ratio means that a 10 foot image without
zoom would be a 14 foot image with full zoom. Conversely, a 10 foot
diagonal image at 15 feet with no zoom would still be a 10 image at 21
feet at maximum zoom (15 x 1.4 = 21 feet). A zoom lens is "not as bright"
as a fixed lens, and the higher the ratio, the less light output.
Top