Overview of
DLP TV
(Digital Light Processing)
Info on DLP Projection TV
Digital Light Processing
(DLP) - Projection
The most likely heir to CRT rear-projection TVs used today is the DLP (Digital Light Processing)
rear-projection TV. Like LCD, the actual image is displayed on a chip, however, the chip used
in a DLP projection TV is quite different. The chip in a DLP projection TV is called a DMD
(Digital Micromirror Device). In essence, every pixel on a DMD chip is a reflective mirror.
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.
That process makes the grayscale foundation for the image. Then, colour is added as light passes
through a high-speed colour 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 together with
the rapidly spinning colour wheel creates the actual colour structure of the projected image.
As the amplified light bounces off the micromirrors, it's sent through the lens, reflected off a large
single mirror, and then onto the screen.
DLP Video Projection advantages
DLP projection is suited for not only for projection TV for home use, but DLP is also in
used in some cinemas to show feature films.
The films are digitally converted and stored to either to a hard drive or optical disc (similar to DVD - but
in High Definition), then fed into the DLP projector and projected onto the screen. The high resolution
DLP chips made for this give an image that is almost as good as 35 or 70mm film, without all those
film scratches!
Some other advantages of the DLP projection are excellent colour accuracy, no
"chickenwire" 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 the LCD kinds
but much "smoother" looking). DLP means you get a very thin depth cabinet, just like LCD
rear-projection sets.
DLP Video Projection - some restrictions
Just like LCD, each DLP chip has a limited amount of pixels.
I can tell you that even though DLP rear-projection doesn't show the "chickenwire"
effect of a lot of LCD-based sets, a DLP rear-projection TV can have something else that can
be annoying. It's known as "the rainbow effect".
I'd describe the "rainbow effect" as seeing a momentary flash of colours (like glancing at a
little rainbow) when you quickly look from side to side on the screen or if you look rapidly
from the screen to side of the room you're in. Thankfully, this doesn't happen too often.
Most people don't actually experience the effect at all.
It's not perfect, but DLP projection has become a definite clear choice among many home
cinema users.
Rear Projection Televisions - other parts used
The are other things needed for a rear-projection TV to work. I've put them here for you in case
you're minded to get some more info.
Projection Lenses
I think it's useful to have an idea of the types of lenses used to magnify the projected image. There are
usually several lense elements put together.
It's normal for a rear-projection TV to have four or five lens elements. Some TVs have more.
Several successive lens are actually needed to maintain a good shape and brightness for the
image.
It's quite easy for just a single lens to make things look really good in the center
of an image, but as the light and image content is spread over the area needed for the size
of screen, further lens elements are needed to maintain an overall image shape so that things
in the image look the same on the sides and corners as in the center of the screen.
As to the actual construction of the lens assemblies, "all-glass" are the best, especially in
surviving high temperature variations from internal and external factors.
Many manufacturers
use a combination of glass and acrylic-based lens construction. This may well not be so bad,
but there can be differences seen, not only in the final image, but overall image performance over
a period of time. Before buying a rear-projection TV, it's bets to check the manufacturers' website
for any info about the sort of lenses they use.
Mirrors
The next element in a rear-projection TV is the mirror.
Because the image must be projected onto a large surface within a relatively small
space (when you compare it to a standard video projector and screen) a mirror is placed in the
way of the projection element, magnifying lenses, and screen. This allows the projection elements
and magnifying lenses to be located at the bottom of the projection TV cabinet. This gives the
projected image a somewhat longer path to the screen so that a bigger image can be put out
as well redirecting the projected image so that it will be facing you correctly.
The Screen
The next element of a rear-projection TV is the screen on which you will see the image. The kind of screen used in projection TVs is very different from those for front video projection
or film. A rear-projection TV screen is made up of two primary elements.
Firstly, there is the inner Fresnel surface, which then further magnifies and spreads the image
brightness across the screen.
Secondly, there is an outer Lenticular surface, which helps in the ultimate shape of the image,
as well as the contrast and the width of the TV viewing angle.
If you touch a rear-projection TV
screen (something you shouldn't ever do normally) you would notice that its surface
isn't smooth like a standard film or video projection screen. That's because you are really touching
the Lenticular surface which is etched into the screen.
The Box
Finally, the last part of a rear-projection TV is the box in which all the elements are sealed. The actual size of the box depends on the size of the screen surface. Rear projection TVs
can be of any size. In practice, they come in sizes of 41-inch to 76-inch screens.
The size of
the box correct for you is determined by your room size and/or your viewing distance from the TV
screen.
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