f you haven't
seen a plasma display by now, you've surely heard about them. Plasma
display panelsor PDPs, for shortare one of the hottest
display products available. It's easy to see why: they combine big,
bright images with wide viewing angles while cutting down on weight
and depth. To many people, plasma displays are the incarnation of
the "television you can hang on a wall" envisioned by science fiction
writers many years ago.
what is plasma?
While the idea of a super- flat TV or computer monitor is pretty
cool, you're probably wondering just how plasma works in the first
place. In a nutshell, plasma panels are made up of thousands of
tiny pixels, created when two ribbed structures are attached at
right angles to each other. The ribs themselves are coated with
color phosphorsred, green, and blueand the sealed pixels
contain a rare gas mixture (such as argon and neon), plus three
When voltage is discharged across the pixel, the gas inside
temporarily changes to a "plasma" state, and actually conducts
the electrical charge from one terminal to another. As it does
this, the gas emits a burst of ultraviolet light, which in turn
causes the color phosphor in that pixel to glow brightly.
To best understand the concept, you need look no further than
the ordinary fluorescent lamp, which also operates as a "plasma"
device. When you turn one on, a device in the lamp creates a high-voltage
discharge to "fire" the lamp. Once the lamp is turned on, a lower
"sustain" voltage keeps it operating, until it is switched off.
The tiny pixels within a plasma panel are charging and discharging
at very high speedsfast enough to show video and high-refresh-rate
graphics. A technique known as Pulse Width Modulation provides
varying levels of brightness, using the ratio of "on" and "off"
pixel states in a given time interval to determine light intensity.
screen size and pixel counts
Plasma panels are manufactured using a silk-screen process and are
available as small as 25" and as large as 60". The shapes of the
panel can resemble a computer monitor (4:3 or 5:4 aspect ratios),
or they can take on the shape of a widescreen TV (16:9 aspect ratio).
The actual pixel count of a panel is independent of the screen sizethere
are 25" displays with SXGA (1280 x 1024 pixel) native resolution,
and 50" panels with wide XGA (1365 x 768 pixel) resolution.
Fujitsu is one of the leading manufacturers of plasma displays,
having begun research and development of plasma technology way
back in the late 1960s. (The first working plasma panels were
invented at the University of Illinois in 1963.) Fujitsu started
shipping full-color models in the United States in 1996, and currently
offers two PDPsthe 42" widescreen PDS-4208, with wide VGA
(852 x 480 pixel) resolution, and the review unit, a PDS-4221
42" widescreen panel with high-definition resolution (1024 x 1024
At first glance, the 1024 x 1024 pixel resolution doesn't make
sense. Intuitively, these numbers would mean a square panel, not
16:9. But Fujitsu uses a non-square pixel that resembles a tiny
16:9 brick, which explains the widescreen aspect ratio. This technique
was perfected so Fujitsu could develop a high-resolution panel
using the same assembly line and tooling used for its wide VGA
When you first look at the PDS-4221, your reaction is generally:
where are the controls? The no-frills frame around the panel (which
provides strength and a duct for cooling air) has a couple of
indicator lamps, and that's ituntil you find the drop-down
control panel, directly under the center of the frame. The basic
panel can't stand on it's own. Unlike some manufacturers, Fujitsu
doesn't provide built-in legs, so you'll need to purchase the
accessory stand (P-42TT11-H) or wall brackets (also available)
to support it.
A separate remote comes with the panel, and it has a minimum
of buttons. In addition to Power On/Off, there's an RGB input
selector which chooses signals at either the 15-pin VGA connector
or a row of five BNC jacks, and a VIDEO input selector which chooses
between the same 5xBNC row or three other BNC jacks for component
video. This is where you'd connect a DVD player or a digital television
The panel's menu structure appears with very crude-looking characters.
It boasts a full range of available adjustments, including image
brightness and contrast, color saturation and hue, and sharpness.
With computer signals, you can adjust their size and position
on the screen, as well as brightness and contrast. You can select
from several picture aspect ratios if you want to fill the image,
including two Wide modes for widescreen DVDs and two Zoom modes
for enlarging regular images to fill the screenalthough
with either some image "squashing" or cropping will result.
on the test bench
An auto-detect circuit in the PDS-4221 does its best to match the
signal from your computer to the panel's display resolution, but
doesn't always work. In my tests, I connected 25 different computer
video signal standards to the panel to see how many it would lock
up on and give me a clean picture. These rates started at VGA-1
(31.5 kHz scan, 70Hz refresh) and went up to 1600 x 1280 UXGA (89.3kHz
scan, 67Hz refresh.)
The PDS-4221 was able to produce clean pictures from 10 input
signals, while three more required some fiddling with the menu,
and one wouldn't display cleanly at all. In addition, 11 signals
resulted in an "Out of Range" menu display. In general, the PDS-4221
will display all VGA, SVGA, and most XGA input signals, but I
wouldn't use it to view any higher-resolution computer images.
In video mode, things were a bit more predictable. Video signals
from both my Sony DVP-S7000 DVD player and a Panasonic TU-DST51
DTV set-top box locked up immediately with the correct aspect
ratio and picture-sync format. HDTV receivers use a three-wire
component video format (YPbPr) similar to that of DVD players
(YCbCr), but this component format is different from the four-
(RGBS) and five- (RGBHV) wire formats used by computers.
If the panel doesn't automatically detect the correct signal
formatand many don'tthen you may get an all-green
or all-pink image, which has to be corrected by going into the
panel's menu and changing a setting. Fortunately, the PDS-4221
has enough smarts to make that changeover automatically, leaving
you to just change from "VIDEO" to "RGB" input modes and vice-versa.
While video signals presented correctly, image quality was not
up to par. Plasma panels suffer from a unique malady known as
"false contouring," or the "creeping moss" effect. A false contour
in an electronic image is caused when the image isn't sampled
sufficiently. You can see this effect by changing the setting
on your computer's display monitor from 16.7 million colors to
256 colors, and looking at a still photograph.
Where there is a gradual change in brightness from medium to
low levels of gray, an artificial boundary will be seen. This
is a false contour, and the PDS-4221 has plenty of them when displaying
movies from DVD and even HDTV signals. At present, there is no
external fix for false contouringit can only be handled
by changing the driving electronics in the panel, and even modifying
the way the pixels are addressed.
Two other manufacturers have already come close to eliminating
false contours (Pioneer and Panasonic), so it's reasonable to
expect Fujitsu will get a handle on this problem in the near future.
In the meantime, if you need a plasma panel to display still images
with mostly mid- to high- tones of color, you probably won't notice
and care about this effect.
In terms of brightness, the PDS-4221 is one of the best performers
out there. After setting the brightness and contrast controls
to their correct levels with test patterns, I measured 90.5 candelas
per square meter (cd/m2) with a full white pattern. That's 25%
brighter than a reference TV monitor, and 40% brighter than my
18" desktop LCD monitor.
Tests with a checkerboard pattern showed the panel to have an
average contrast ratio of 153:1, which is comparable to a good
CRT video or computer monitor. Peak contrast was measured at 186:1,
so you'll get plenty of contrast from this panel. However, the
black levels are on the high side at .7 cd/m2, and you'll see
a dark gray instead of a dense black when the panel is switched
on with no signals present.
Color saturation is quite good, and you can select from one
of four color temperatures: cool, normal, warm, and studio. The
first two are a bit on the blue side, and generally used to view
computer graphics. The Warm mode is used to display video and
HDTV, and will make flesh tones and yellow and red colors look
more natural. The Studio setting results in an almost orange image,
but is designed so the panel will look correctly on the set of
a TV program.
I liked many things about the PDS-4221. There's no question
it looks best with computer graphics, and it does an acceptable
job with high-definition video. Regular video suffers from the
false contouring problem and isn't nearly as crisp as it could
be. The user interface is easy, but the menus look too crude and
should be updated. Although the PDS-4221 can't correctly size
many computer sync rates, it works well enough with the most common
signals and is smart enough to sort them out from component video.
Peter H. Putman, a Certified Technology Specialist, is
president of ROAM Consulting, Inc., which provides consulting and
marketing communications services to manufacturers, dealers, and
end-users of large-screen display products. Putnam currently writes
for Video Systems, Sound & Video Contractor, Millimeter, Etown.com,
and Church Production.
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