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Getting
Inside the Box of Your Home Theater System
Designing your home theater system is getting more exciting
all the time. Televisions are bigger, better, cheaper, and
slimmer than ever. The home theater consumer has choices ranging
from the traditional tube-type television to large screen
rear projection sets, to the latest hang-on-the-wall Plasma
and LCD flat panel monitors. All of these types of television
configurations have been successfully incorporated into many
home theaters around the world. However, all of these TV viewing
options place the viewer "outside the box" (so to
speak). All of the work of generating the video image (from
input to display) is done within an "enclosed box"
of some type. The box is also a piece of furniture that takes
up space either on a floor, table, or wall.
On the other hand, the movie theater
places the viewer "inside the box".
You enter a special environment where
curtains open up, revealing the screen, a hidden film projector
(or digital cinema projector) then starts up, and the room
is enveloped in image and sound. The image is projected from
behind or above and is reflected off the screen. You are within
the image environment as the beams of light travel from the
projection unit to the screen. That is what separates most
home theaters from the movie theater.
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Making
Your Own Home Theater Magic
How can one capture the same "magic" as a trip to
the movie theater? You can come very close with your own home
theater projection setup. Of course, such units have been
around for some time, but they were big, bulky, power hogs,
and very, very, expensive; definitely out of reach for the
average consumer.
However, as an outgrowth, in recent
years, of the need for compact, affordable, portable multi-media
projection units for use in business presentations, new technological
developments in image processing have made this once out-of-reach
option more affordable for use in home theater by more and
more consumers.
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Video
Projection Vs Film Projection
The video projector is similar to a film or slide projector
in that they both accept a source, and project the image from
that source onto a screen. However, that is where the similarity
ends. Inside a video projector is processing circuitry that
converts an analog or digital video input signal into something
that can be projected onto a screen.
If you haven't considered the projector
option, you may find that it may fit your home theater setup.
However, there are some basic things you need to know before
you can get started.
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CRT
Projector Overview
Currently, there are three basic types of video projector
technology in common use today: CRT, LCD, and DLP. There are
also variations of these three types (including D-ILA and
LCOS).
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The
CRT Projector (Cathode Ray Tube)
When video projectors first arrived on the scene, television
technology was based on the Cathode Ray Tube (CRT), on which
the viewer sees the television image. Three small CRTs (one
for each primary color), coupled with a light magnifying lens,
can project a color image onto a large screen in a darkened
room. With the proper video processing circuitry, CRT size,
and lens combination, a CRT projector can produce excellent
high resolution images.
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Advantages
Of The CRT Video Projector
1. The image in a CRT projector is scanned
with an electron beam (just as in regular tube TV) and is
not limited to a fixed pixel field, as are other video projector
types (to be discussed, in more detail, later in this article).
This makes the CRT projector the best option where the flexibility
of displaying variable resolutions is the main consideration.
2. A CRT projector
can produce the blackest blacks of all projector types as
well as the full range of color, giving a CRT projector the
ability to project the most film-like images of projectors
for home use.
3. In addition, another
advantage of the CRT projector is its long projection life
(as long as 20,000 hours), compared to other types. With LCD
and DLP video projectors (described on the following pages)
the light source must be replaced every 1,000 to 2,000 hours
to maintain optimum brightness and contrast. This amounts
to an added regular expense of several hundred dollars every
two years or so, depending on usage.
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Limitations
Of The CRT projector
1. A CRT projector is, typically, very large.
In order to house the optimum CRT and lens size combination
to project onto a large screen, with enough brightness, a
CRT projector can take up as much space as a 20-inch TV (tube
facing down). This makes it less portable if you need to travel
with it or place it in another room.
2. A CRT projector,
typically, is not as bright as other types of projectors.
The ability to have a completely dark room is necessary.
3. A CRT projector
has to be converged properly for best image reproduction.
Since the modern CRT projector houses three projection tubes
(red, green, and blue), the tubes need to be aligned so that
the projected image does not exhibit color halos and the colors
are mixed correctly. Also, if one projection tube fails, all
three have to be replaced in order to provide the correct
color and brightness balance.
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LCD
Projector Overview - The LCD Projector (Liquid Crystal Display)
The second video projector type to consider is the LCD (Liquid
Crystal Display) projector. Unlike a CRT projector, the LCD
projector is not based on the traditional projection tube.
An LCD projector basically works by passing a powerful light
source through a transparent LCD chip made up of individual
pixels (which displays the moving video image) and projecting
that image through a lens to a large screen.
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The
Advantage Of The LCD Projector
What makes the LCD projector very practical is that it is
compact, since the LCD chip is very small. One LCD chip is
hundreds of times smaller than the three projection tubes
needed in CRT projectors. Other advantages of the LCD projector
are its high contrast and brightness capability, as well as
lower power consumption.
This combination of factors makes
the LCD projector very portable for multimedia use, such as
business presentations (even in partially lit rooms). Also,
with some modification, an LCD projector can provide an excellent
option for home theater use. Probably the final "hook"
is that an LCD projector is fairly inexpensive, when compared
to CRT types.
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Limitations Of The LCD Projector
1. An LCD projector can often times exhibit
what is called "the screen door effect". Since the
screen is made up of individual pixels, the pixels can be
visible on a large screen, thus giving the appearance of viewing
the image through a "screen door".
2. When using a business-type
LCD projector in a home theater setup, the image may appear
too harsh with regards to brightness and contrast.
3. Since an LCD chip
is made up of a panel of individual pixels, if one pixel burns
out it displays an annoying black or white dot on the projected
image. Individual pixels cannot be repaired, if one or more
pixels burn out, the entire chip has to be replaced.
4. Since LCD chips
have a finite number of pixels, signal inputs that have higher
resolutions must be scaled to fit the pixel field count of
the particular LCD chip. For example, a typical HDTV input
format of 1080i needs a native display of 1920x1080 pixels
for a one-to-one display of the HDTV image. However, if your
LCD chip only has a pixel field of 1024x768, the original
HDTV signal must be scaled to fit the 1024x768 pixel count
on the LCD chip (in addition the image will also have to be
letterboxed to reproduce the correct widescreen aspect ratio).
This is where CRT projectors can excel over an LCD projector,
since they are not limited by a fixed pixel field; they are
more flexible at displaying various resolutions, due to being
able to variably scan the image onto the projection tube surface.
5. As mentioned earlier,
the LCD light source (bulb) in an LCD projector must be replaced
periodically, depending on the projector, about every 1,000
to 2,000 hours, at a cost of several hundred dollars. On the
positive side of this, a new lamp basically gives you a new
LCD projector, as your original brightness and contrast are
restored, and most bulbs can be self-installed by the consumer.
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Variants
of LCD
Other variants of LCD video projection technology in use are:
LCOS (Liquid Crystal on Silicon), D-ILA
(Digital Imaging Light Amplification), and SXRD
(Silicon Crystal Reflective Display).
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DLP
Projector Overview - The DLP Projector (Digital Light Processing)
The fastest growing type of video projector (in terms of sales)
in use today is the DLP (Digital Light Processing) projector.
Like LCD, the actual image is displayed on a chip; however,
the chip used in a DLP projector is different. The chip in
a DLP projector is referred to as a DMD (Digital Micromirror
Device). In essence, every pixel on a DMD chip is a reflective
mirror.
The video image is displayed on the
DMD chip. The micromirrors on the chip (remember: each micromirror
represents one pixel) then tilt very rapidly as the image
changes. This process produces the grayscale foundation for
the image. Then, color is added as light passes through a
high-speed color wheel and is reflected off of the micromirrors
on the DLP chip as they rapidly tilt towards or away from
the light source.
The degree of tilt of each micromirror
coupled with the rapidly spinning color wheel determines the
color structure of the projected image. As the amplified light
bounces off the micromirrors, it is sent through the lens
and can be projected on a large screen.
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The
Advantage Of The DLPProjector
The advantages of this system make the DLP projector suitable
for not only business and home theater application, but DLP
technology is also in use in some movie theaters for feature
film projection. Basically the films are digitally converted
and stored to either to a hard drive or optical disc (similar
to DVD - only in High Definition), then fed into the DLP projector
and projected onto the movie screen. The high resolution DLP
chips made for this application render an image that is almost
as good as 35 or 70mm film, without all those film scratches!
Other advantages of the DLP projector
include excellent color accuracy, no "screen door"
effect(as with LCD), due to its micro-mirror construction,
compactness, low power consumption, and high contrast and
brightness (although typically not as bright as LCD types
but much "smoother" looking).
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Limitations
Of The DLP Projector
1. Just as with LCD, each DLP chip has a
finite number of pixels.
2. Although a DLP
projector doesn't exhibit the "screen door" effect
of many LCD units, a DLP projector can exhibit what is referred
to as "the rainbow effect". Basically, the "rainbow
effect" is exhibited by a brief flash of colors (like
a small rainbow) when the viewer rapidly looks from side to
side on the screen or looks rapidly from the screen to side
of the room. Fortunately, this does not occur frequently and
many people do not have sensitivity to this effect at all.
3. Just as in LCD
projectors, the light source must be changed every 1,000 to
2,000 hours.
Although DLP isn't perfect, the DLP
projector has become a real favorite amongst home theater
enthusiasts.
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The
Bottom Line: What To Look For
Choosing a projector boils down to: What you want to watch
(and where), Portability (if necessary), Brightness, Contrast
Ratio, Pixel Density, Color Reproduction, Inputs, and Screen.
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Best
Uses For A Video Projector
Home theater projectors are best for viewing Sports and DVD
movies. If you watch mostly regular TV, an LCD/DLP projector
may be an expensive option as the bulb would need to be changed
after 1,000 to 2,000 hours of viewing (some projectors now
have upwards of 3,000 bulb life; and this continues to improve).
Also, make sure you have the proper room size for your projector.
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Portability
Portability is important; not just enabling you to move or
travel with your projector, but simplifies installation and
setup. It also makes it easy to try different screen sizes,
distances, and different rooms to see what works best.
If your projector is portable you
can even hang a sheet on an outside wall (or garage door)
in the summertime and enjoy your own drive-in movies!
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Brightness
Brightness: Without sufficient brightness your image will
look muddy and soft, even in a dark room. Check the ANSI Lumens
rating. Relatively speaking, projectors with 1,000 ANSI Lumens
or greater have sufficient brightness for home theater use.
Room size and screen size/distance will affect the need for
more or less lumens.
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Contrast
Ratio
Contrast Ratio complements brightness. High contrast ratios
deliver whiter whites and blacker blacks. A projector may
have a great Lumens rating, but if the contrast ratio is low,
you image will look washed out. Contrast ratios of at least
1,500:1 are good, but 2,000:1 or higher is considered excellent.
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Pixel
Density and Scaling
Pixel Density is important, especially for LCD/DLP units.
As stated earlier, LCD and DLP-based video projectors have
a fixed number of pixels on their display chips. If most of
your viewing is HDTV, get as high a native pixel count as
possible. A native pixel count of 1024x768 is sufficient for
DVD. However, 720p HDTV signals require a 1280x720 pixel count
to give you a one-for-one representation of a 720p signal
while, as mentioned earlier, a 1080i HDTV input signal needs
a native pixel count of 1920x1080 for a one-for-one representation
of the 1080i signal.
If a projector's pixel count is less
and it accepts HDTV input signals, the signal is scaled to
fit the number of pixels on the chip. In addition, some projectors
also upscale a lower resolution image to match a higher pixel
count on the chip. Scaling can work both ways. Check specifications
for this capability.
If the projector has a good built-in
scaler, the image should look smooth, and fairly consistent,
no matter what the input source is (however, other factors,
such as a poor film source print, degraded VHS video, and
degraded color or gray scale consistency on the source material
can affect results). Scaling cannot correct for poor source
material, but can make your source look as good as it can
look, based on the projector's native pixel field. There are
also outboard video scalers and processors than can be used,
which are often preferred in high-end video projection installations,
especially if the projector is being used to project a very
large image.
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Color
Reproduction
Color Reproduction is another factor. Check for natural flesh
tones and color depth. Check how colors look in the brightest
and darkest areas of the image. Check the degree of color
stability from input to input. Everyone has a slight difference
in color perception and what looks pleasing. Look carefully.
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Inputs
Make sure the projector has the inputs you need, such composite
and S-video for analog sources, component inputs for DVD,
and DVI or HDMI inputs for HDTV. Most projectors also have
VGA-type inputs for computers.
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Don't
Forget About The Screen
Screens come in various fabrics, sizes, and prices. You could
use that old 8mm film projection screen or just put up a sheet,
but to get the most out of your projector, a good screen is
necessary. The type of screen that's best depends on the projector,
the viewing angle, the amount of ambient light in the room,
and the distance of the projector from the screen. The iNet
Home Theaters professionals have selected the optimal screens
for your use within the “Front Projection Systems.”
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