Technology
CRT (Cathode Ray Tube) Monitors
Still the most common type of monitor and capable of producing outstanding
visual results. An electron beam is fired down the back-end of the
monitor (or 'tube') and hits the screen. The inside of the screen
is coated with a special type of phosphor that produces light when
struck by these electrons the colour produced depends on the
formulation of phosphor used.
Brightness is controlled
by the voltage passed through the monitor that results in more or
less electrons being fired at the screen. The electron beam scans
from left-to-right and from top-to-bottom to form a grid. The picture
is formed by controlling the brightness of each point or
pixel (short for picture element) on this
grid. The number of times per second that this grid is redrawn by
the beam is called the refresh rate.
Colour monitors use phosphor dots or strips of red, green and blue
in pixels that are so closely grouped that the eye cannot make out
the individual colours. These primary colours can thus be used to
generate any colour required.
There are two major CRT technologies: Shadow
Mask and Aperture Grill.
Shadow Mask CRTs
This type of CRT has a metal mesh placed just behind the screen that
separates out the beams of the three guns (red, green and blue) so
that they only hit the correct colour dot of phosphor. The width of
each of these dots is called the dot
pitch and, generally speaking, the smaller the better.
Originally, Shadow Mask CRTs were noticeably spherical in shape but
now the vast majority are of the FST
(Flat Square Tube) design that results in a much flatter screen and
hence less distorted or curved images.
The Shadow
Mask CRT design offers clear
character formation, accurate
colour rendition and offers
good price/performance.
Aperture Grill CRTs
Instead of
using a metal mesh like the
Shadow Mask CRT, the Aperture
Grill CRT uses vertical wires
held under tension behind
which the phosphor coating
is painted on in strips (red,
green, blue) instead of dots.
As there is less metal, more of the
energy is turned into light
and not heat. There is also
a greater area of phosphor
so brightness is generally
improved. This additional
brightness allows a darker
tinted screen to be used,
which in turn allows higher
contrast. And finally, the
screen shape is cylindrical
(rather than spherical) which
reduces reflections.
Flat CRT Monitors
The next
step for the CRT is monitors
that are not just flatter
but completely flat. These
technologies can be based
on either the shadow mask
or aperture grill CRT design.
The advantages of a truly
flat screen are two-fold:
glare and reflections from
sunlight or artificial light
are significantly reduced
and the warping of images
by the curve of the screen
is eliminated. To achieve
a flat screen display, a special
electron gun must be used
that can vary it's focal length
as there is no longer a curved
screen to negate this issue.
Current flat
CRT technologies include the
Diamondtron™ (shadow
mask), Flatron™ (shadow
mask) and the FD Trinitron™
(aperture grill). Each of
these technologies will use
different technological approaches.
For example, the FD Trinitron™
has a flat screen with a convex
phosphor strip behind it to
deliver visually (not just
physically) flat picture.
The important point is that
each of these new CRT technologies
aims to deliver totally flat
pictures.
LCD Monitors
LCD monitors
are becoming more and more
popular due to their flat,
space-saving design and picture
quality that has improved
massively over the past few
years. They are also more
economical to run than CRTs
and have a longer service
life.
LCD (Liquid
Crystal Displays) generate
images by using special chemicals
called Liquid Crystals through
which the amount of light
transmitted can be controlled
by electric fields that rotate
the crystals. The screen is
divided up into picture elements
(pixels) and colour LCDs use
pixels fitted with red, green
or blue filters to produce
all of the different colours.
LCD Technologies
The first form of LCD technology uses liquid crystal molecules called
Twisted Nematic (TN).
These twisted molecules are controlled by transistors that apply a
voltage to a group of sub-pixels (red, green and blue). This electric
current rotates them so that the appropriate level of light and colour
is let through. They are usually described as TN + film LCDs as manufacturers
usually add a film that helps to improve the viewable angle. This
type of LCD offers excellent price/performance though, as the 'default'
setting for each pixel is to let light through, dead pixels are a
noticeable white.
Other LCD technologies include In-Plane Switching (IPS),
Super In-Plane Switching (SIPS)
and Multi-Domain Vertical Alignment (MVA).
IPS and SIPS LCDs use a second filter that
is perpendicular to the first
one so that if no voltage
is applied the pixel remains
black. This means dead pixels
are much less noticeable as
they are black rather than
white. IPS LCDs may also provide
better viewable angles than
TN LCDs. The main limitations
of IPS technology is that
it requires more power and
may have a slower response
time (important for fast moving
pictures) than a TN LCD.
MVA LCDs have the crystals of each
subpixel aligned in a number
of different directions and
each crystal is able to rotate
independently. This creates
a wide range of display 'zones'
so that users will only perceive
one zone, no matter where
they are in relation to the
screen. The viewable angle
is thus very good, the contrast
ratio is very high and the
response time may be better
than TN or IPS/SIPS equivalents.
However, whilst the image
is viewable from a range of
angles, colours will often
be distorted unless viewed
from head-on.
Projectors
Projectors magnify smaller images to
a size that is suitable for
group viewing or public display.
They will often be used for
office meetings, presentations
to clients or at lectures
or conferences. The main criteria
users should assess when selecting
a projector are brightness
(usually measured in ANSI
lumens), contrast ratio (the
difference in light intensity
between the brightest white
and deepest black), uniformity
(how consistent the light
and colour is throughout the
image), resolution, weight
and noise. You may also want
to consider which extra features
you will need such as digital
zoom, built-in speakers, HDTV
compatibility, picture in
picture, etc.
Projector Technologies
There are four main front projection technologies: Liquid Crystal
Display (LCD), Digital
Light Processors (DLP),
Liquid Crystal on Silicon Devices (LCOS)
and Cathode Ray Tube (CRT).
LCD projectors
are the most commonly used
as they are efficient, robust
and reliable. Using Liquid
Crystal technology, an image
made up of a pixel grid is
projected onto a single mirror
which reflects it through
a lens for magnification and
focusing. They provide excellent
colour performance and are
equally adept at displaying
both data and video images.
They are also relatively economical
to buy, though you will need
to purchase a model with a
high brightness capability
(1600+ lumens) if you wish
to use this type of projector
in an environment with high
ambient light e.g. lit room.
DLP projectors
are particularly effective
at displaying video images.
A single DLP chip has the
entire pixel grid on it and
every pixel on that chip has
its own separate reflective
mirror that helps to amplify
the light being generated.
Since each pixel has its own
amplified light source, there
is virtually no limit to the
picture size because brightness
and contrast will always be
consistent. They are small,
lightweight and very easy
to carry around, though their
small size means they are
liable to become hotter than
an LCD projector.
LCOS projectors
use very small LCDs mounted
on top of reflective silicon
chips that generate an image
with very high pixel counts.
They therefore offer greater
resolution than their peers,
though contrast performance
may suffer. The high image
quality means they are especially
useful when displaying video.
CRT projectors
are still used where very
high resolutions are required
or outstanding video performance
is essential. They are considerably
larger than other types of
projector as they require
three separate colour tubes
(red, green and blue). They
are also much better at displaying
images at a range of different
resolutions than other projection
technologies. |
Resolution
Display
Resolutions
You will
undoubtedly come across the
term 'resolution' when you
are comparing monitors. The
resolution is simply how many
pixels that make up the screen
image horizontally by how
many pixels there are vertically
e.g. 1024x768 is a grid of
1024 pixels from left-to-right
and 768 from top-to-bottom.
CRT Resolutions
The higher
the screen resolution, the
smaller each image becomes
and the sharper the image
may appear. So, to put it
simply, the larger your CRT
monitor screen size, the higher
you will want to set your
resolution to take advantage
of it. For example, someone
using a very large monitor
to do complex CAD work may
want to run it at a super
high resolution of 2048x1536
in order to maintain the necessary
level of detail and information
on screen. Conversely, someone
doing word processing on a
15" monitor will probably
want to run it at 800x600
so that the font is large
enough to comfortably read.
It is also
important to note that the
higher the resolution, the
lower the refresh rate, as
your monitor will be having
to redraw more pixels each
time the screen is refreshed
e.g. 800x600 = 480,000 pixels
whereas a resolution of 1024x768
= 786,432 pixels. If your
refresh rate becomes too low
(less than 75hz) then this
will result in noticeable
screen flicker and potentially
lead to eye strain and an
associated headache.
Each of these resolution rates has a standard name such as VGA
(Video Graphics Array) or XGA
(Extended Graphics Array). These standards were mainly used prior
to operating systems like Windows that could run in a number of resolutions
but you may still come across them.
LCD Resolutions
LCD resolutions are different from CRTs as they are fixed-matrix displays
they have a set amount of pixels on each screen. This fixed
grid of pixels is called the native
resolution of the LCD and it is highly recommended
that this resolution be used. By using complex algorithms to subdivide
each pixel an LCD can be run in lower resolutions, but this will often
result in blocky results and is not usually recommended.
Recommended Resolutions
Here are the Modes, Resolution, number of pixels and recommended resolution
rates for each screen size of CRT and LCD:
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Recommended CRT screen size |
Recommended TFT screen size
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